text:
Gifts of Real Estate
Donating appreciated real estate, such as a home, vacation property, undeveloped land, farmland, ranch or commercial property can make a great gift to Free Will Baptist.
Benefits of gifts of real estate
- Avoid paying capital gains tax on the sale of the real estate
- Receive a charitable income tax deduction based on the value of the gift
- Leave a lasting legacy to Free Will Baptist
How to make a gift of real estate
Your real property may be given to Free Will Baptist by executing or signing a deed transferring ownership. You may deed part or all of your real property to Free Will Baptist. Your gift will generally be based on the property's fair market value, which must be established by an independent appraisal.
Contact us
If you have any questions about gifts of real estate, please contact us. We would be happy to assist you and answer any questions that you have.
Additional Information
Mortgaged Property - Please contact us if the property you wish to give has existing debt or a mortgage. Indebtedness can affect your charitable tax deduction.
Difficult Property Gifts - Certain properties pose challenges. We have adopted policies to limit the acceptance of certain kinds of real estate. Please check with us before making a gift of real estate so we can explain our gift acceptance policies.
Capital Gains Tax - Check with us on the capital gains tax implications of your gift. You may also be interested in life income options.


text:
Create the perfect fit for your travel plans by grabbing one of our 8 Bedroom Smokies vacation rentals. Whether you need to spread out or want to stay close, our rentals accommodate you at every turn.
Book My Cabin & Save 15%!
Enjoy the perfect Smoky Mountain vacation with your loved ones at Bar Mountain IV.
Nestled in beautiful mountains near Pigeon Forge, TN, likes Mountain View Pool Lodge.
Turn your vacation to the Sevierville area into paradise staying at The Oasis.
Experience an incredible escape to the Smoky Mountains by staying at the lovely Waldens Creek Oasis.
Take your Smoky Mountain vacation to a new level by staying at the gorgeous Pool and a Theater Lodge.
Preparing Search Results
Please be patient, this may take a minute.
Interested in receiving our newsletter? Simply provide your full name and email address in these fields to begin receiving information. By doing so, you can learn about special promotions and events in the Smoky Mountains!
We respect our customer's privacy and feel it is disrespectful to bombard anyone with emails. We treat all information that customers share with us as private and confidential. Deer Path Cabins never shares this information with third party sites.
Arrival Date: Mandatory, select or enter date you will arrive (MM/DD/YYYY)
Nights: Mandatory, select or enter the number of Nights you will be staying with us
Promotional Code: Must enter a valid code
Optional Search Items: (Amenties, Cities, etc) Below are several boxes in which you can either select from a drop down list or click on a check box to the left of an item to select.
Changing the contents of any drop down list or selecting/deselecting a check box will broaden or narrow the number of properties displayed by your search. You don't have to wait until the search completes to select/deselect items for your perfect search.
You must hit the SEARCH button to start your first search. It is unnecessary to hit the SEARCH button after doing your first search, unless you changed to another web page, changed the Arrival Date or number of Nights.
Add to Favorites: As you visit individual property pages or pages with listings of several properties on them, you have the option to click on the "+ Favorites" for each particular property, which automatically adds the property to your list of Favorites for consideration. The number next to the Favorites tab, left sidebar, will increase up to 99 possible Favorites. When ready, click on the Favorites tab to view a list of your selected Favorites.
Remove from Favorites: You may de-select (remove) properties from your Favorites you no longer wish to consider by either clicking on the minus icon to the right or by clicking on the "- Favorites" displayed on property list pages and each property details page for properties listed in your Favorites.
Compare Favorites: Click in the check boxes to the left of the property name, in your Favorites, you wish to compare. No more than 3 boxes may be selected at one time. When ready, hit the Compare button for a comparison of the 3 selected properties.
Follow the above "Remove from Favorites" instructions to remove a property from the comparison and your Favorites.
To add another property from your Favorites list for comparison, click the check box to the left of the property name in your Favorites and hit the Compare button.
Repeat the above steps to find your ultimate vacation accommodations. Need assistance or have questions, please give us a call so we may better serve you!
View List: Displays a full list of all your Favorites with some details.
Remove All: Clears all properties from your Favorites so you may start over.

subset: commoncrawl


text:
With this week's hostage debacle in Algeria — which killed 23 oil workers and 32 hostages, and ended in a fiery assault on Saturday — international energy companies operating in the region are left grappling with an urgent question: Can they keep their personnel safe amid the region's political upheaval amplified by the conflict in Mali, where French forces have intervened to stop government forces being overrun by jihadist militants?
At stake are billions of dollars in investment in the wider Maghreb and West Africa by dozens of Western companies. The assumption that energy installations in the region were safe from terrorist attacks collapsed before dawn on Wednesday, when armed militants invaded the living quarters of Algeria's In Amenas gas facility in the remote southeastern part of the country, seizing hundreds of hostages, both local and foreign — among them American, British, Japanese, French and Norwegian oil workers. The impact of that attack, for which Algerian jihadist commander Mokhtar Belmokhtar claimed responsibility, will likely be felt for years.
"Oil companies will have to factor in completely different security measures," says Fadel Gheit, a senior energy analyst at the New York City–based investment bank Oppenheimer & Co. "These facilities are absolutely naked."
(MORE: Algeria's Hostage Crisis: What Was Behind a Shadowy Militant Leader's Plot?)
The biggest impact of the hostage debacle will be on Algeria itself, which relies on energy production for 95% of its exports and more than 60% of its total revenues. The In Amenas plant, a joint venture with BP and Norway's Statoil, accounts for more than 10% of the country's natural-gas output. Foreign companies began evacuating their staff from Algeria immediately after the kidnappings, and on Friday, British Prime Minister David Cameron told Parliament that security had been beefed up around Western commercial and diplomatic facilities elsewhere in the region too.
There is no knowing when oil companies will deem it safe to return expatriate staff to Algeria, let alone risk plowing billions into new energy projects; Algeria has been courting Western investment, not only in its hydrocarbon sector but also to finance such renewable-energy plans as solar plants in the vast Algerian Sahara. At minimum, potential investors will now drive a harder bargain, given the additional expenses they would have to incur on security in order to expand their infrastructure in Algeria. "Operating in Algeria has just become more expensive," Eurasia Group's Africa director Philippe de Pontet says in a memo sent to clients on Friday. "Assets sold in the coming 12 to 18 months with have a significant discount applied."
The new threat to their economy's economic lifeline has shaken ordinary Algerians. "People are very worried," Hocine Lambriben, a reporter at Algeria's al-Watan newspaper, told TIME on Friday from Algiers. "For many years, these facilities were presented to us like impregnable fortresses where site security was guaranteed," he said. "It would be catastrophic if other facilities were targeted by jihadists. Foreign oil companies would likely reconsider their presence in Algeria."
(MORE: Westerners Kidnapped in North Africa — but Is France the Real Target?)
For now, oil companies are not disclosing their plans. Still, a glance at the map of North Africa is enough to show the depth of the security challenge they face. Western oil companies involved in Chad and Nigeria could now be more vulnerable, since each country has deployed hundreds of troops to join the French-led war in Mali, against which the jihadist kidnappers in Algeria claimed — possibly opportunistically — to be retaliating. And Nigeria is already fighting a domestic battle with the violent Islamist Boko Haram movement, an ideological fellow traveler of the Mali insurgents.
The dangers expand elsewhere, with huge oil reserves attracting Western companies to set up production across the vast Sahel. South of Algeria and Mali sits Niger, a dirt-poor desert country with the world's fourth largest output of uranium, which supplies France's crucial network of nuclear power stations. East of Algeria is Libya, where a number of Western companies exploit some of Africa's biggest oil reserves, but where security remains plagued by militant groups like the one that killed four Americans in an attack on the U.S. consulate in Benghazi last September.
(MORE: The Crisis in Mali: Will French Air Strikes Stop the Islamist Advance?)
As more countries are drawn into the French-led operation, the dangers could proliferate. "The risk of additional kidnappings and asymmetrical reprisals against French and allied-country targets in North Africa, the Sahel and beyond will rise sharply," de Pontet warns.
On Friday, Libya's Petroleum Faculty Guard announced that it had beefed up its military presence in and around the country's energy facilities. The new measures, it said, include the creation of "a special operations room" to monitor oil-and-gas plants. Such measures are late in coming. Gheit says he has been shocked at what he perceives to be inadequate security in a country awash in weapons and with weaker central authority since the fall of Muammar Gaddafi. "These sites are very, very vulnerable," he told TIME, hours before Libya announced its increased security measures. "If somebody targets these sites, they will get them, there is no question in my mind." It has taken the deaths of a number of foreign and Algerian oil workers to jolt governments into taking long overdue security precautions. Oil companies and the governments that host them will be hoping those actions will be enough to keep oil workers safe and their Western partners from leaving.


text:
Endlessly adaptable.Component based.Built to last a lifetime.
Includes4x Leg, 85 cm4x Leg, 115 cm8x End Caps and Safety Clip Set1x Tall Cabinet2x Shelf, 85 x 35 cm1x Backplate, 75 x 25
(Inner shelf for the cabinet is sold separately)
MaterialShelves: FSC-certified oak veneerLegs: Powder coated steel
Size200 x 85 x 35 cm (H x W x D)
Watch the video
Denmark*Free shipping on orders above 500 DKKHome delivery: 60 DKK / Business delivery: 40 DKKDelivery estimate: 4-5 working days
*For shipments to Greenland and Faroe Islands please contact us: firstname.lastname@example.com (excluding Norway, Switzerland and United Kingdom)Free shipping on orders above €150Home delivery: €8 / Business delivery: €8Delivery estimate: 4-8 working days
Norway and SwitzerlandFree shipping on orders above €150Home delivery: €20Delivery estimate: 4-8 working days
United Kingdom (including NI)Free shipping on orders above £130Home delivery: €18Delivery estimate: 5-10 working days
We do not currently ship to other countries, but our products are sold in many retailers around the world. You can use our retailer locator to find your closest one.
Please contact email@example.com regarding shipment of larger quantities.
How deep are the shelves?
The shelves are 17.5 cm deep.
Is it glued or screwed?
No, it is just held by the wedges.
Do I need to fix it to a wall?
Yes. Wall Shelving System comes included with fixing brackets. These should be installed at the top, bottom and at every leg interval.
How do I know that the shelf is straight?
By using a water level, a water level app or measuring the distance between the shelves.
How much weight can it stand?
We do not recommend more than 10 kg on each shelf.
Does the wood change colour?
Direct sunlight will cause the colour of wood to change, even if it is stained or lacquered. This will be particularly apparent if the furniture is placed under eg. a window. Oak will tend to darken in this situation.
What are the shelves made of?
The wedges are made from solid oak and the shelves are made from an MDF core with either an oiled or black-stained oak finish or a white PU paint.
Where is it produced?
In Lithuania.
How high and wide can it be built?
You can build the system as high and wide as you like. There are no limitations.
What colours does it come in?
Shelves - Oiled oak Veneer / Black stained oak veneer / White PU paint
Legs - Powder coated in black or white
What if I lose a part?
If you lose a part, e.g. a wedge, you can always get hold of our replacement part from the spare parts section of our website.
How do I remove stains from e.g. a cup?
Light stains may be removed by gently rubbing in the direction of the grain with 400 grit (very fine) sandpaper and re-oiling afterward.
How do I clean the Shelving System?
Dust can be removed with damp cloth.
How do I remove dry patches on the surface?
Apply a thin coat of oil to the furniture with a clean lint-free cloth to nourish the wood. Do not use oils sold for cooking or eating.
When unwrapped it might take 2–3 days for the protective oil to completely dry. Be careful to protect clothing and other materials that can soak up oil during this time.
If at any time the wood displays lighter dry patches, we recommend you apply a thin coat of oil to the furniture with a clean lint-free cloth to nourish the wood. Small cans of pigment free furniture oil are available from most DIY or hardware stores. Do not use oils sold for cooking or eating.
Any spills must be removed immediately using a cloth. Dust can be removed with damp a cloth. Light stains may be removed by gently rubbing in the direction of the grain with 400 grit (very fine) sandpaper and re-oiling afterwards.
If you don't find what you are looking for, don't hesitate to send us an email: email@example.com
The shelves are 35 cm deep.
We do not recommend to use the Shelving System without securing it to the wall. If doing so please beware that it is your responsibility to make sure, that it is constructed so it will not fall over.
How do I know when it's straight?
We do not recommend more than 20 kg on each shelf. If you have a backplate below the shelf the recommended limit is 30 kg.
Direct sunlight will cause the colour of real wood to change, even if it is stained or lacquered. This will be particularly apparent if the furniture is placed under eg. a window. Oak will tend to darken in this situation.
Can I buy different parts?
Yes, you can buy all parts separately and design your shelving system how ever you like.
If you lose a part, e.g. a wedge, you can always email us to get a new specific part.
How to delete a part
1. Select the part that you want to remove by clicking on it.
2. Once selected. Click on the recycle bin image located at the bottom right of the model screen. The part should now be removed.
How to rotate a bay
Bays can only be rotated when adding a new bay to the system. Select a ''corner extension '' right or left.
How to rotate


text:
Our direct replacement Airtek je-c0800 meets or exceeds OEM specifications. This product is aftermarket only and we are not affiliated with Airtek. Photos are for illustrative purposes only and depict the broad types of products offered.
If we ship the incorrect item, we will replace. We will send you an RMA to return the incorrect part. We will notify you of estimated time of shipment.
All of our products are direct replacement aftermarket only. We are not affiliated with the OEM companies.
If allowed all return goods will be subject to approval by the manufacture and will include a minimum restocking charge of at least 25% less the original freight costs. If the item is not commonly carried, special ordered, made to order or extremely long lead time the restocking fee will reflect that of the manufacturer. Some items will be non returnable. No freight costs will be credited or reimbursed period. Compressor oil and lubricants are non returnable. No goods may be returned without prior authorization by CAS. Contact Customer Service please contact us at email@example.com for a Returned Goods Authorization (RGA) number. Return authorization is valid for 30 days only. Products shipped in error will be accepted for return with full credit. Shipping discrepancies must be brought to the attention of CAS 24 hours of receipt of shipment. If a return is allowed the returned products must be in original package, in new saleable condition and shipped freight prepaid. CAS reserves the right to determine acceptability of the returned goods for resale. Products made to order are not returnable.
Warranty and Limitation of Liability
Compressed Air Specialists may change its terms at any time without notification.
This warranty applies to products manufactured and/or distributed by Compressed Air Specialists when they are properly installed on the correct application, used in the conditions and service they were designed for and where CAS instructions have been followed. CAS warrants all products sold to be free from defects in material and workmanship as long as they are changed in accordance with the original equipment manufacturers recommendations. For all air/oil, gas separators and refrigeration coalescer applications, this warranty shall terminate six months from the date of the original purchase invoice or after 1000 hours of in service use, whichever occurs first. For parts sold, but not manufactured by CAS, those manufacturers warranties shall apply.
In order to obtain possible product warranty consideration, the original purchaser must first notify CAS in writing, within ten (10) days of discovering the alleged problem. The original purchaser must also provide documentation of application usage, product service life, a description of the alleged defect and other information on the CAS Returned Goods Information form. Upon receipt of this notification, CAS will either examine the product in question at the customer's location or issue a product return authorization. When requested, the product in question must be returned to CAS in its original condition, prepaid, in a condition where it can be resold. PLEASE NOTE: ALL returned products may be subject to destructive testing and evaluation procedures. This warranty does not apply to product misapplication, altered products, improper product installation or shipping damage. If one of our products is determined by CAS personnel to be defective, CAS's sole obligation under this warranty shall be to repair or replace the product, at our option, without charge to the original purchaser, or repay the original purchase price. In no event shall CAS be liable for any direct, indirect, consequential or special damages, including loss of profits or business or for any claims whether arising from breach of contract or warranty or claims of negligence or negligent manufacture in excess of the original product purchase price.
This warranty is exclusive and in lieu of all other warranties, expressed or implied including, but not limited to warranties of merchantability and fitness for any particular purpose.
Visible or Noted Loss or Damage, Concealed Loss or Damage is the responsibility of the customer (receiver of the shipment) period. We will not refund any money or ship replacement items at no charge when it comes do damage visible or concealed. CAS must be notified of all shortages within 24 hours. We are unable to help you if there is damage of any kind please see the information below
UPS claim information
FedEx claim information
Shipping within the lower 48 US states
Many items ship within two to three business days. Some may take longer during this unprecedented time. We will notify you of delivery once we receive confirmation from our supplier. If you need to cancel due to the shipping date we will refund your money. If you need specific delivery information, special handling, or air freight shipping please contact us at email@example.com or call toll free 833-260-3103. Freight charges will be additional on special shipping requests or items not listed on our website. We can ship UPS or FedEx on you collect account.
Pricing and free freight offers subject to change without notice. We will notify you of a price correction or that we are unable to offer free freight. We will give full credit and you may repurchase at the corrected price. Any flagged credit card orders will be shipped when the funds clear our bank. We will not refund any wire transfer charges incurred from refunding wire payments
CAS must be notified of all shortages within 24 hours of you receiving the shipment and will check our inventory to validate the shortage. Freight carriers are in between the supplier and the customer. Be sure to thoroughly inspect all items upon receiving them. Once you sign for the package and the freight carrier leaves you accept that the shipment is yours and you take responsibility. Then it is very difficult to file a freight claim. PLEASE CHECK YOUR PACKAGE CAREFULLY. Visible damage or Noted Loss or Damage, Concealed Loss or Damage is the responsibility of the customer (receiver of the shipment) period. We will not refund any money or ship replacement items at no charge when it comes do damage visible or concealed. If you suspect concealed damage, you must note something like "Possible Freight Damage" on the delivery receipt while the driver is present. This way, if you discover later that the product is damaged filing a freight claim is much easier. Do not sign for "Obvious Damage". Take pictures. Make a note and contact us immediately where we can process that the package is being returned. We are unable to help you if there is damage of any kind please see the information below
International shipping
All international shipments must ship freight collect to the destination. We are unable to quote shipping rates. We will gladly use your freight forwarder or shipping carrier. We are able to quote product size and sometimes weight but it may take a little while to get the information. Visible or Noted Loss or Damage, Concealed Loss or Damage is the responsibility of the customer (receiver of the shipment) period. We will not refund any money or ship replacement items at no charge when it comes do damage visible or concealed. CAS must be notified in writing via email email@example.com of all shortages within 24 hours.
New items added daily
Airtek ame-01-e Element, Mist Eliminator Direct Replacement
$ 235.00
Airtek ame-02-e Element, Mist Eliminator Direct Replacement
$ 225.40
Airtek ame-03-e Element, Mist Eliminator Direct Replacement
$ 250.00
Airtek ame-04-e Element, Mist Eliminator Direct Replacement
$ 424.00
Airtek ame-05-e Element, Mist Eliminator Direct Replacement
$ 620.00


text:
Our Privacy Policy
Below we set out our privacy policy which will govern the way in which we process any personal information that you provide to us. Our details are :
shown on this sites contact page.
The site owner can be contacted at the email address on this sites contact page
You can access our home page and browse certain areas of the site without disclosing your personal data save information collected by cookies that we may use (see below).
Who may Process Data
Your personal information (which includes your name, address and any other details you provide to us which concern you as an individual) may be processed both by us and by other companies within our group. Each of the companies authorised to process your information as mentioned above will do so in accordance with this privacy policy. When you place an order via this website we will store your e-mail address along with any other information you may provide. When you use the services on the website, we may need to collect further information about you. This information may include, but is not limited to, details such as your name and address.
Purpose of Processing
We will use your information for the purpose of providing you with information about our services, articles and news, fulfilling orders placed by you, processing any other transactions authorised or made by you with us, informing you of special offers and providing other marketing information to you which we think you may find of interest, undertaking product or customer research/development.
Disclosure of Information
In the unlikely event that a liquidator, administrator or receiver is appointed over us or all or any part of our assets that insolvency practitioner may transfer your information to a third party purchaser of the business provided that purchaser undertakes to use your information for the same purposes as set out in this policy. Your information will not be disclosed to government or local authorities or other government institutions save as required by law or other binding regulations.
We may send a small file to your computer when you visit our website. This will enable us to identify your computer, track your behaviour on our website and to identify your particular areas of interest so as to enhance your future visits to this website. We may use cookies to collect and store personal data and we link information stored by cookies with personal data you supply to us. Save for the use of cookies, we do not automatically log data or collect data save for information you specifically provide to us. You can set your computer browser to reject cookies but this may preclude your use of certain parts of this website.
We have implemented security policies, rules and technical measures to protect the personal data that we have under our control from unauthorised access, improper use and disclosure, unauthorised destruction or accidental loss.
All website design, text, graphics, the selection and arrangement thereof are owed by the company running this site, or hosting this site, except where provided under the General Public License (http://www.gpl.org). ALL RIGHTS RESERVED.
All trademarks of are the property of their respective owners and may be registered in certain parts of the world.
Disclaimer of Warranty and Liability
The following provisions may be curtailed or disallowed by the laws of certain jurisdictions. In such case, the terms hereof are to be read as excluding or limiting such term so as to satisfy such law.
We do not represent or warrant that the information accessible via this website is accurate, complete or current. We have no liability whatsoever in respect of any use which you make of such information.
The information provided on this website has not been written to meet your individual requirements and it is your sole responsibility to satisfy yourself prior to ordering any products or services from us that they are suitable for your purposes.
Whilst we make all reasonable attempts to exclude viruses from the website, we cannot ensure such exclusion and no liability is accepted for viruses. Thus, you are recommended to take all appropriate safeguards before downloading information or images from this website.
All warranties, express or implied, statutory or otherwise are hereby excluded.
Neither we nor any of our employees or affiliated entities will be liable for any kind of damages and howsoever arising including, without limitation, loss of profits, compensatory, consequential, direct, exemplary, incidental, indirect, punitive or special, damages or any liability which you may have to a third party, even if we have been advised of the possibility of such loss.
We are not responsible for the direct or indirect consequences of you linking to any other website from this website.
These terms and this disclaimer and any claim based on use of information from this website shall be governed by the laws of England and Wales and you agree to submit to the non-exclusive jurisdiction of the Courts of England.
Consent and enquiries
By continuing to use this site and accessing the information on this website, you signal acceptance of the terms and disclaimer set out above. If you do not accept any of these terms, leave this website now. If you have any enquiry or concern about our privacy policy or the way in which we are handling personal data please contact email. If at any time you wish us to cease processing your information please send a message to the Administrator at the email address on this sites contact page.


text:
perlipc - Perl interprocess communication (signals, fifos, pipes, safe subprocesses, sockets, and semaphores)
The basic IPC facilities of Perl are built out of the good old Unix signals, named pipes, pipe opens, the Berkeley socket routines, and SysV IPC calls. Each is used in slightly different situations.
Perl uses a simple signal handling model: the %SIG hash contains names or references of user-installed signal handlers. These handlers will be called with an argument which is the name of the signal that triggered it. A signal may be generated intentionally from a particular keyboard sequence like control-C or control-Z, sent to you from another process, or triggered automatically by the kernel when special events transpire, like a child process exiting, your own process running out of stack space, or hitting a process file-size limit.
For example, to trap an interrupt signal, set up a handler like this:
our $shucks;
sub catch_zap {
my $signame = shift;
die "Somebody sent me a SIG$signame";
$SIG{INT} = __PACKAGE__ . "::catch_zap";
$SIG{INT} = \&catch_zap; # best strategy
Prior to Perl 5.7.3 it was necessary to do as little as you possibly could in your handler; notice how all we do is set a global variable and then raise an exception. That's because on most systems, libraries are not re-entrant; particularly, memory allocation and I/O routines are not. That meant that doing nearly anything in your handler could in theory trigger a memory fault and subsequent core dump - see "Deferred Signals (Safe Signals)" below.
The names of the signals are the ones listed out by kill -l
on your system, or you can retrieve them from the Config module. Set up an @signame list indexed by number to get the name and a %signo hash table indexed by name to get the number:
use Config;
defined($Config{sig_name}) || die "No sigs?";
foreach $name (split(" ", $Config{sig_name})) {
$signo{$name} = $i;
$signame[$i] = $name;
So to check whether signal 17 and SIGALRM were the same, do just this:
print "signal #17 = $signame[17]\n";
if ($signo{ALRM}) {
print "SIGALRM is $signo{ALRM}\n";
You may also choose to assign the strings "IGNORE"
or "DEFAULT"
as the handler, in which case Perl will try to discard the signal or do the default thing.
On most Unix platforms, the CHLD
(sometimes also known as CLD
) signal has special behavior with respect to a value of "IGNORE"
. Setting $SIG{CHLD}
to "IGNORE"
on such a platform has the effect of not creating zombie processes when the parent process fails to wait()
on its child processes (i.e., child processes are automatically reaped). Calling wait()
with $SIG{CHLD}
set to "IGNORE"
usually returns -1
on such platforms.
Some signals can be neither trapped nor ignored, such as the KILL and STOP (but not the TSTP) signals. One strategy for temporarily ignoring signals is to use a local() on that hash element, automatically restoring a previous value once your block is exited. Remember that values created by the dynamically-scoped local() are "inherited" by functions called from within their caller's scope.
sub precious {
local $SIG{INT} = "IGNORE";
sub more_functions {
# interrupts still ignored, for now...
Sending a signal to a negative process ID means that you send the signal to the entire Unix process group. This code sends a hang-up signal to all processes in the current process group, and also sets $SIG{HUP} to "IGNORE"
so it doesn't kill itself:
# block scope for local
local $SIG{HUP} = "IGNORE";
kill HUP => -$$;
# snazzy writing of: kill("HUP", -$$)
Another interesting signal to send is signal number zero. This doesn't actually affect a child process, but instead checks whether it's alive or has changed its UID.
unless (kill 0 => $kid_pid) {
warn "something wicked happened to $kid_pid";
When directed at a process whose UID is not identical to that of the sending process, signal number zero may fail because you lack permission to send the signal, even though the process is alive. You may be able to determine the cause of failure using %!
unless (kill(0 => $pid) || $!{EPERM}) {
warn "$pid looks dead";
You might also want to employ anonymous functions for simple signal handlers:
$SIG{INT} = sub { die "\nOutta here!\n" };
But that will be problematic for the more complicated handlers that need to reinstall themselves. Because Perl's signal mechanism is currently based on the signal(3) function from the C library, you may sometimes be so unfortunate as to run on systems where that function is "broken"; that is, it behaves in the old unreliable SysV way rather than the newer, more reasonable BSD and POSIX fashion. So you'll see defensive people writing signal handlers like this:
sub REAPER {
$waitedpid = wait;
# loathe SysV: it makes us not only reinstate
# the handler, but place it after the wait
# now do something that forks...
or better still:
use POSIX ":sys_wait_h";
sub REAPER {
my $child;
# If a second child dies while in the signal handler caused by the
# first death, we won't get another signal. So must loop here else
# we will leave the unreaped child as a zombie. And the next time
# two children die we get another zombie. And so on.
while (($child = waitpid(-1, WNOHANG)) > 0) {
$Kid_Status{$child} = $?;
$SIG{CHLD} = \&REAPER; # still loathe SysV
# do something that forks...
Be careful: qx(), system(), and some modules for calling external commands do a fork(), then wait() for the result. Thus, your signal handler (&REAPER
in the example) will be called. Because wait() was already called by system() or qx(), the wait() in the signal handler will see no more zombies and will therefore block.
The best way to prevent this issue is to use waitpid(), as in the following example:
use POSIX ":sys_wait_h"; # for nonblocking read
my %children;
$SIG{CHLD} = sub {
# don't change $! and $? outside handler
local ($!, $?);
my $pid = waitpid(-1, WNOHANG);
return if $pid == -1;
return unless defined $children{$pid};
delete $children{$pid};
cleanup_child($pid, $?);
while (1) {
my $pid = fork();
die "cannot fork" unless defined $pid;
if ($pid == 0) {
# ...
exit 0;
} else {
# ...
# ...
Signal handling is also used for timeouts in Unix. While safely protected within an eval{}
block, you set a signal handler to trap alarm signals and then schedule to have one delivered to you in some number of seconds. Then try your blocking operation, clearing the alarm when it's done but not before you've exited your eval{}
block. If it goes off, you'll use die() to jump out of the block, much as you might using longjmp() or throw() in other languages.
Here's an example:
my $ALARM_EXCEPTION = "alarm clock restart";
eval {
local $SIG{ALRM} = sub { die $ALARM_EXCEPTION };
alarm 10;
flock(FH, 2) # blocking write lock
|| die "cannot flock: $!";
alarm 0;
if ($@ && $@ !~ quotemeta($ALARM_EXCEPTION)) { die }
If the operation being timed out is system() or qx(), this technique is liable to generate zombies. If this matters to you, you'll need to do your own fork() and exec(), and kill the errant child process.
For more complex signal handling, you might see the standard POSIX module. Lamentably, this is almost entirely undocumented, but the t/lib/posix.t file from the Perl source distribution has some examples in it.
A process that usually starts when the system boots and shuts down when the system is shut down is called a daemon (Disk And Execution MONitor). If a daemon process has a configuration file which is modified after the process has been started, there should be a way to tell that process to reread its configuration file without stopping the process. Many daemons provide this mechanism using a SIGHUP
signal handler. When you want to tell the daemon to reread the file, simply send it the SIGHUP
Not all platforms automatically reinstall their (native) signal handlers after a signal delivery. This means that the handler works the first time the signal is sent, only. The solution to this problem is to use POSIX
signal handlers if available; their behavior is well-defined.
The following example implements a simple daemon, which restarts itself every time the SIGHUP
signal is received. The actual code is located in the subroutine code()
, which just prints some debugging info to show that it works; it should be replaced with the real code.
#!/usr/bin/perl -w
use POSIX ();
use FindBin ();
use File::Basename ();
use File::Spec::Functions;
$| = 1;
# make the daemon cross-platform, so exec always calls the script
# itself with the right path, no matter how the script was invoked.
my $script = File::Basename::basename($0);
my $SELF = catfile($FindBin::Bin, $script);
# POSIX unmasks the sigprocmask properly
my $sigset = POSIX::SigSet->new();
my $action = POSIX::SigAction->new("sigHUP_handler",
POSIX::sigaction(&POSIX::SIGHUP, $action);
sub sigHUP_handler {
print "got SIGHUP\n";
exec($SELF, @ARGV) || die "$0: couldn't restart: $!";
sub code {
print "PID: $$\n";
print "ARGV: @ARGV\n";
my $count = 0;
while (++$count) {
sleep 2;
print "$count\n";
Before Perl 5.7.3, installing Perl code to deal with signals exposed you to danger from two things. First, few system library functions are re-entrant. If the signal interrupts while Perl is executing one function (like malloc(3) or printf(3)), and your signal handler then calls the same function again, you could get unpredictable behavior--often, a core dump. Second, Perl isn't itself re-entrant at the lowest levels. If the signal interrupts Perl while Perl is changing its own internal data structures, similarly unpredictable behavior may result.
There were two things you could do, knowing this: be paranoid or be pragmatic. The paranoid approach was to do as little as possible in your signal handler. Set an existing integer variable that already has a value, and return. This doesn't help you if you're in a slow system call, which will just restart. That means you have to die
to longjmp(3) out of the handler. Even this is a little cavalier for the true paranoiac, who avoids die
in a handler because the system is out to get you. The pragmatic approach was to say "I know the risks, but prefer the convenience", and to do anything you wanted in your signal handler, and be prepared to clean up core dumps now and again.
Perl 5.7.3 and later avoid these problems by "deferring" signals. That is, when the signal is delivered to the process by the system (to the C code that implements Perl) a flag is set, and the handler returns immediately. Then at strategic "safe" points in the Perl interpreter (e.g. when it is about to execute a new opcode) the flags are checked and the Perl level handler from %SIG is executed. The "deferred" scheme allows much more flexibility in the coding of signal handlers as we know the Perl interpreter is in a safe state, and that we are not in a system library function when the handler is called. However the implementation does differ from previous Perls in the following ways:
As the Perl interpreter looks at signal flags only when it is about to execute a new opcode, a signal that arrives during a long-running opcode (e.g. a regular expression operation on a very large string) will not be seen until the current opcode completes.
If a signal of any given type fires multiple times during an opcode (such as from a fine-grained timer), the handler for that signal will be called only once, after the opcode completes; all other instances will be discarded. Furthermore, if your system's signal queue gets flooded to the point that there are signals that have been raised but not yet caught (and thus not deferred) at the time an opcode completes, those signals may well be caught and deferred during subsequent opcodes, with sometimes surprising results. For example, you may see alarms delivered even after calling alarm(0)
as the latter stops the raising of alarms but does not cancel the delivery of alarms raised but not yet caught. Do not depend on the behaviors described in this paragraph as they are side effects of the current implementation and may change in future versions of Perl.
When a signal is delivered (e.g., SIGINT from a control-C) the operating system breaks into IO operations like read(2), which is used to implement Perl's readline() function, the <>
operator. On older Perls the handler was called immediately (and as read
is not "unsafe", this worked well). With the "deferred" scheme the handler is not called immediately, and if Perl is using the system's stdio
library that library may restart the read
without returning to Perl to give it a chance to call the %SIG handler. If this happens on your system the solution is to use the :perlio
layer to do IO--at least on those handles that you want to be able to break into with signals. (The :perlio
layer checks the signal flags and calls %SIG handlers before resuming IO operation.)
The default in Perl 5.7.3 and later is to automatically use the :perlio
Note that it is not advisable to access a file handle within a signal handler where that signal has interrupted an I/O operation on that same handle. While perl will at least try hard not to crash, there are no guarantees of data integrity; for example, some data might get dropped or written twice.
Some networking library functions like gethostbyname() are known to have their own implementations of timeouts which may conflict with your timeouts. If you have problems with such functions, try using the POSIX sigaction() function, which bypasses Perl safe signals. Be warned that this does subject you to possible memory corruption, as described above.
Instead of setting $SIG{ALRM}
local $SIG{ALRM} = sub { die "alarm" };
try something like the following:
use POSIX qw(SIGALRM);
POSIX::SigAction->new(sub { die "alarm" }))
|| die "Error setting SIGALRM handler: $!\n";
Another way to disable the safe signal behavior locally is to use the Perl::Unsafe::Signals
module from CPAN, which affects all signals.
On systems that supported it, older versions of Perl used the SA_RESTART flag when installing %SIG handlers. This meant that restartable system calls would continue rather than returning when a signal arrived. In order to deliver deferred signals promptly, Perl 5.7.3 and later do not use SA_RESTART. Consequently, restartable system calls can fail (with $! set to EINTR
) in places where they previously would have succeeded.
The default :perlio
layer retries read
, write
and close
as described above; interrupted wait
and waitpid
calls will always be retried.
Certain signals like SEGV, ILL, and BUS are generated by virtual memory addressing errors and similar "faults". These are normally fatal: there is little a Perl-level handler can do with them. So Perl now delivers them immediately rather than attempting to defer them.
On some operating systems certain signal handlers are supposed to "do something" before returning. One example can be CHLD or CLD, which indicates a child process has completed. On some operating systems the signal handler is expected to wait
for the completed child process. On such systems the deferred signal scheme will not work for those signals: it does not do the wait
. Again the failure will look like a loop as the operating system will reissue the signal because there are completed child processes that have not yet been wait
ed for.
If you want the old signal behavior back despite possible memory corruption, set the environment variable PERL_SIGNALS
to "unsafe"
. This feature first appeared in Perl 5.8.1.
A named pipe (often referred to as a FIFO) is an old Unix IPC mechanism for processes communicating on the same machine. It works just like regular anonymous pipes, except that the processes rendezvous using a filename and need not be related.
To create a named pipe, use the POSIX::mkfifo()
use POSIX qw(mkfifo);
mkfifo($path, 0700) || die "mkfifo $path failed: $!";
You can also use the Unix command mknod(1), or on some systems, mkfifo(1). These may not be in your normal path, though.
# system return val is backwards, so && not ||
$ENV{PATH} .= ":/etc:/usr/etc";
if ( system("mknod", $path, "p")
&& system("mkfifo", $path) )
die "mk{nod,fifo} $path failed";
A fifo is convenient when you want to connect a process to an unrelated one. When you open a fifo, the program will block until there's something on the other end.
For example, let's say you'd like to have your .signature file be a named pipe that has a Perl program on the other end. Now every time any program (like a mailer, news reader, finger program, etc.) tries to read from that file, the reading program will read the new signature from your program. We'll use the pipe-checking file-test operator, -p, to find out whether anyone (or anything) has accidentally removed our fifo.
chdir(); # go home
my $FIFO = ".signature";
while (1) {
unless (-p $FIFO) {
unlink $FIFO; # discard any failure, will catch later
require POSIX; # delayed loading of heavy module
POSIX::mkfifo($FIFO, 0700)
|| die "can't mkfifo $FIFO: $!";
# next line blocks till there's a reader
open (FIFO, "> $FIFO") || die "can't open $FIFO: $!";
print FIFO "John Smith (smith\@host.org)\n", `fortune -s`;
close(FIFO) || die "can't close $FIFO: $!";
sleep 2; # to avoid dup signals
Perl's basic open() statement can also be used for unidirectional interprocess communication by either appending or prepending a pipe symbol to the second argument to open(). Here's how to start something up in a child process you intend to write to:
open(SPOOLER, "| cat -v | lpr -h 2>/dev/null")
|| die "can't fork: $!";
local $SIG{PIPE} = sub { die "spooler pipe broke" };
print SPOOLER "stuff\n";
close SPOOLER || die "bad spool: $! $?";
And here's how to start up a child process you intend to read from:
open(STATUS, "netstat -an 2>&1 |")
|| die "can't fork: $!";
while (<STATUS>) {
next if /^(tcp|udp)/;
close STATUS || die "bad netstat: $! $?";
If one can be sure that a particular program is a Perl script expecting filenames in @ARGV, the clever programmer can write something like this:
% program f1 "cmd1|" - f2 "cmd2|" f3 < tmpfile
and no matter which sort of shell it's called from, the Perl program will read from the file f1, the process cmd1, standard input (tmpfile in this case), the f2 file, the cmd2 command, and finally the f3 file. Pretty nifty, eh?
You might notice that you could use backticks for much the same effect as opening a pipe for reading:
print grep { !/^(tcp|udp)/ } `netstat -an 2>&1`;
die "bad netstatus ($?)" if $?;
While this is true on the surface, it's much more efficient to process the file one line or record at a time because then you don't have to read the whole thing into memory at once. It also gives you finer control of the whole process, letting you kill off the child process early if you'd like.
Be careful to check the return values from both open() and close(). If you're writing to a pipe, you should also trap SIGPIPE. Otherwise, think of what happens when you start up a pipe to a command that doesn't exist: the open() will in all likelihood succeed (it only reflects the fork()'s success), but then your output will fail--spectacularly. Perl can't know whether the command worked, because your command is actually running in a separate process whose exec() might have failed. Therefore, while readers of bogus commands return just a quick EOF, writers to bogus commands will get hit with a signal, which they'd best be prepared to handle. Consider:
open(FH, "|bogus") || die "can't fork: $!";
print FH "bang\n"; # neither necessary nor sufficient
# to check print retval!
close(FH) || die "can't close: $!";
The reason for not checking the return value from print() is because of pipe buffering; physical writes are delayed. That won't blow up until the close, and it will blow up with a SIGPIPE. To catch it, you could use this:
open(FH, "|bogus") || die "can't fork: $!";
print FH "bang\n";
close(FH) || die "can't close: status=$?";
Both the main process and any child processes it forks share the same STDIN, STDOUT, and STDERR filehandles. If both processes try to access them at once, strange things can happen. You may also want to close or reopen the filehandles for the child. You can get around this by opening your pipe with open(), but on some systems this means that the child process cannot outlive the parent.
You can run a command in the background with:
system("cmd &");
The command's STDOUT and STDERR (and possibly STDIN, depending on your shell) will be the same as the parent's. You won't need to catch SIGCHLD because of the double-fork taking place; see below for details.
In some cases (starting server processes, for instance) you'll want to completely dissociate the child process from the parent. This is often called daemonization. A well-behaved daemon will also chdir() to the root directory so it doesn't prevent unmounting the filesystem containing the directory from which it was launched, and redirect its standard file descriptors from and to /dev/null so that random output doesn't wind up on the user's terminal.
use POSIX "setsid";
sub daemonize {
chdir("/") || die "can't chdir to /: $!";
open(STDIN, "< /dev/null") || die "can't read /dev/null: $!";
open(STDOUT, "> /dev/null") || die "can't write to /dev/null: $!";
defined(my $pid = fork()) || die "can't fork: $!";
exit if $pid; # non-zero now means I am the parent
(setsid() != -1) || die "Can't start a new session: $!"
open(STDERR, ">&STDOUT") || die "can't dup stdout: $!";
The fork() has to come before the setsid() to ensure you aren't a process group leader; the setsid() will fail if you are. If your system doesn't have the setsid() function, open /dev/tty and use the TIOCNOTTY
ioctl() on it instead. See tty(4) for details.
Non-Unix users should check their Your_OS::Process
module for other possible solutions.
Another interesting approach to IPC is making your single program go multiprocess and communicate between--or even amongst--yourselves. The open() function will accept a file argument of either "-|"
or "|-"
to do a very interesting thing: it forks a child connected to the filehandle you've opened. The child is running the same program as the parent. This is useful for safely opening a file when running under an assumed UID or GID, for example. If you open a pipe to minus, you can write to the filehandle you opened and your kid will find it in his STDIN. If you open a pipe from minus, you can read from the filehandle you opened whatever your kid writes to his STDOUT.
use English qw[ -no_match_vars ];
my $PRECIOUS = "/path/to/some/safe/file";
my $sleep_count;
my $pid;
do {
$pid = open(KID_TO_WRITE, "|-");
unless (defined $pid) {
warn "cannot fork: $!";
die "bailing out" if $sleep_count++ > 6;
sleep 10;
} until defined $pid;
if ($pid) { # I am the parent
print KID_TO_WRITE @some_data;
close(KID_TO_WRITE) || warn "kid exited $?";
} else { # I am the child
# drop permissions in setuid and/or setgid programs:
open (OUTFILE, "> $PRECIOUS")
|| die "can't open $PRECIOUS: $!";
while (<STDIN>) {
print OUTFILE; # child's STDIN is parent's KID_TO_WRITE
close(OUTFILE) || die "can't close $PRECIOUS: $!";
exit(0); # don't forget this!!
Another common use for this construct is when you need to execute something without the shell's interference. With system(), it's straightforward, but you can't use a pipe open or backticks safely. That's because there's no way to stop the shell from getting its hands on your arguments. Instead, use lower-level control to call exec() directly.
Here's a safe backtick or pipe open for read:
my $pid = open(KID_TO_READ, "-|");
defined($pid) || die "can't fork: $!";
if ($pid) { # parent
while (<KID_TO_READ>) {
# do something interesting
close(KID_TO_READ) || warn "kid exited $?";
} else { # child
($EUID, $EGID) = ($UID, $GID); # suid only
exec($program, @options, @args)
|| die "can't exec program: $!";
And here's a safe pipe open for writing:
my $pid = open(KID_TO_WRITE, "|-");
defined($pid) || die "can't fork: $!";
$SIG{PIPE} = sub { die "whoops, $program pipe broke" };
if ($pid) { # parent
print KID_TO_WRITE @data;
close(KID_TO_WRITE) || warn "kid exited $?";
} else { # child
exec($program, @options, @args)
|| die "can't exec program: $!";
It is very easy to dead-lock a process using this form of open(), or indeed with any use of pipe() with multiple subprocesses. The example above is "safe" because it is simple and calls exec(). See "Avoiding Pipe Deadlocks" for general safety principles, but there are extra gotchas with Safe Pipe Opens.
In particular, if you opened the pipe using open FH, "|-"
, then you cannot simply use close() in the parent process to close an unwanted writer. Consider this code:
my $pid = open(WRITER, "|-"); # fork open a kid
defined($pid) || die "first fork failed: $!";
if ($pid) {
if (my $sub_pid = fork()) {
defined($sub_pid) || die "second fork failed: $!";
close(WRITER) || die "couldn't close WRITER: $!";
# now do something else...
else {
# first write to WRITER
# ...
# then when finished
close(WRITER) || die "couldn't close WRITER: $!";
else {
# first do something with STDIN, then
In the example above, the true parent does not want to write to the WRITER filehandle, so it closes it. However, because WRITER was opened using open FH, "|-"
, it has a special behavior: closing it calls waitpid() (see "waitpid" in perlfunc), which waits for the subprocess to exit. If the child process ends up waiting for something happening in the section marked "do something else", you have deadlock.
This can also be a problem with intermediate subprocesses in more complicated code, which will call waitpid() on all open filehandles during global destruction--in no predictable order.
To solve this, you must manually use pipe(), fork(), and the form of open() which sets one file descriptor to another, as shown below:
pipe(READER, WRITER) || die "pipe failed: $!";
$pid = fork();
defined($pid) || die "first fork failed: $!";
if ($pid) {
close READER;
if (my $sub_pid = fork()) {
defined($sub_pid) || die "first fork failed: $!";
close(WRITER) || die "can't close WRITER: $!";
else {
# write to WRITER...
# ...
# then when finished
close(WRITER) || die "can't close WRITER: $!";
# write to WRITER...
else {
open(STDIN, "<&READER") || die "can't reopen STDIN: $!";
close(WRITER) || die "can't close WRITER: $!";
# do something...
Since Perl 5.8.0, you can also use the list form of open
for pipes. This is preferred when you wish to avoid having the shell interpret metacharacters that may be in your command string.
So for example, instead of using:
open(PS_PIPE, "ps aux|") || die "can't open ps pipe: $!";
One would use either of these:
open(PS_PIPE, "-|", "ps", "aux")
|| die "can't open ps pipe: $!";
@ps_args = qw[ ps aux ];
open(PS_PIPE, "-|", @ps_args)
|| die "can't open @ps_args|: $!";
Because there are more than three arguments to open(), forks the ps(1) command without spawning a shell, and reads its standard output via the PS_PIPE
filehandle. The corresponding syntax to write to command pipes is to use "|-"
in place of "-|"
This was admittedly a rather silly example, because you're using string literals whose content is perfectly safe. There is therefore no cause to resort to the harder-to-read, multi-argument form of pipe open(). However, whenever you cannot be assured that the program arguments are free of shell metacharacters, the fancier form of open() should be used. For example:
@grep_args = ("egrep", "-i", $some_pattern, @many_files);
open(GREP_PIPE, "-|", @grep_args)
|| die "can't open @grep_args|: $!";
Here the multi-argument form of pipe open() is preferred because the pattern and indeed even the filenames themselves might hold metacharacters.
Be aware that these operations are full Unix forks, which means they may not be correctly implemented on all alien systems. Additionally, these are not true multithreading. To learn more about threading, see the modules file mentioned below in the SEE ALSO section.
Whenever you have more than one subprocess, you must be careful that each closes whichever half of any pipes created for interprocess communication it is not using. This is because any child process reading from the pipe and expecting an EOF will never receive it, and therefore never exit. A single process closing a pipe is not enough to close it; the last process with the pipe open must close it for it to read EOF.
Certain built-in Unix features help prevent this most of the time. For instance, filehandles have a "close on exec" flag, which is set en masse under control of the $^F
variable. This is so any filehandles you didn't explicitly route to the STDIN, STDOUT or STDERR of a child program will be automatically closed.
Always explicitly and immediately call close() on the writable end of any pipe, unless that process is actually writing to it. Even if you don't explicitly call close(), Perl will still close() all filehandles during global destruction. As previously discussed, if those filehandles have been opened with Safe Pipe Open, this will result in calling waitpid(), which may again deadlock.
While this works reasonably well for unidirectional communication, what about bidirectional communication? The most obvious approach doesn't work:
open(PROG_FOR_READING_AND_WRITING, "| some program |")
If you forget to use warnings
, you'll miss out entirely on the helpful diagnostic message:
Can't do bidirectional pipe at -e line 1.
If you really want to, you can use the standard open2() from the IPC::Open2
module to catch both ends. There's also an open3() in IPC::Open3
for tridirectional I/O so you can also catch your child's STDERR, but doing so would then require an awkward select() loop and wouldn't allow you to use normal Perl input operations.
If you look at its source, you'll see that open2() uses low-level primitives like the pipe() and exec() syscalls to create all the connections. Although it might have been more efficient by using socketpair(), this would have been even less portable than it already is. The open2() and open3() functions are unlikely to work anywhere except on a Unix system, or at least one purporting POSIX compliance.
Here's an example of using open2():
use FileHandle;
use IPC::Open2;
$pid = open2(*Reader, *Writer, "cat -un");
print Writer "stuff\n";
$got = <Reader>;
The problem with this is that buffering is really going to ruin your day. Even though your Writer
filehandle is auto-flushed so the process on the other end gets your data in a timely manner, you can't usually do anything to force that process to give its data to you in a similarly quick fashion. In this special case, we could actually so, because we gave cat a -u flag to make it unbuffered. But very few commands are designed to operate over pipes, so this seldom works unless you yourself wrote the program on the other end of the double-ended pipe.
A solution to this is to use a library which uses pseudottys to make your program behave more reasonably. This way you don't have to have control over the source code of the program you're using. The Expect
module from CPAN also addresses this kind of thing. This module requires two other modules from CPAN, IO::Pty
and IO::Stty
. It sets up a pseudo terminal to interact with programs that insist on talking to the terminal device driver. If your system is supported, this may be your best bet.
If you want, you may make low-level pipe() and fork() syscalls to stitch this together by hand. This example only talks to itself, but you could reopen the appropriate handles to STDIN and STDOUT and call other processes. (The following example lacks proper error checking.)
#!/usr/bin/perl -w
# pipe1 - bidirectional communication using two pipe pairs
# designed for the socketpair-challenged
use IO::Handle; # thousands of lines just for autoflush :-(
pipe(PARENT_RDR, CHILD_WTR); # XXX: check failure?
pipe(CHILD_RDR, PARENT_WTR); # XXX: check failure?
if ($pid = fork()) {
close PARENT_RDR;
close PARENT_WTR;
print CHILD_WTR "Parent Pid $$ is sending this\n";
chomp($line = <CHILD_RDR>);
print "Parent Pid $$ just read this: `$line'\n";
close CHILD_RDR; close CHILD_WTR;
waitpid($pid, 0);
} else {
die "cannot fork: $!" unless defined $pid;
close CHILD_RDR;
close CHILD_WTR;
chomp($line = <PARENT_RDR>);
print "Child Pid $$ just read this: `$line'\n";
print PARENT_WTR "Child Pid $$ is sending this\n";
close PARENT_RDR;
close PARENT_WTR;
But you don't actually have to make two pipe calls. If you have the socketpair() system call, it will do this all for you.
#!/usr/bin/perl -w
# pipe2 - bidirectional communication using socketpair
# "the best ones always go both ways"
use Socket;
use IO::Handle; # thousands of lines just for autoflush :-(
# We say AF_UNIX because although *_LOCAL is the
# POSIX 1003.1g form of the constant, many machines
# still don't have it.
socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
|| die "socketpair: $!";
if ($pid = fork()) {
close PARENT;
print CHILD "Parent Pid $$ is sending this\n";
chomp($line = <CHILD>);
print "Parent Pid $$ just read this: `$line'\n";
close CHILD;
waitpid($pid, 0);
} else {
die "cannot fork: $!" unless defined $pid;
close CHILD;
chomp($line = <PARENT>);
print "Child Pid $$ just read this: '$line'\n";
print PARENT "Child Pid $$ is sending this\n";
close PARENT;
While not entirely limited to Unix-derived operating systems (e.g., WinSock on PCs provides socket support, as do some VMS libraries), you might not have sockets on your system, in which case this section probably isn't going to do you much good. With sockets, you can do both virtual circuits like TCP streams and datagrams like UDP packets. You may be able to do even more depending on your system.
The Perl functions for dealing with sockets have the same names as the corresponding system calls in C, but their arguments tend to differ for two reasons. First, Perl filehandles work differently than C file descriptors. Second, Perl already knows the length of its strings, so you don't need to pass that information.
One of the major problems with ancient, antemillennial socket code in Perl was that it used hard-coded values for some of the constants, which severely hurt portability. If you ever see code that does anything like explicitly setting $AF_INET = 2
, you know you're in for big trouble. An immeasurably superior approach is to use the Socket
module, which more reliably grants access to the various constants and functions you'll need.
If you're not writing a server/client for an existing protocol like NNTP or SMTP, you should give some thought to how your server will know when the client has finished talking, and vice-versa. Most protocols are based on one-line messages and responses (so one party knows the other has finished when a "\n" is received) or multi-line messages and responses that end with a period on an empty line ("\n.\n" terminates a message/response).
The Internet line terminator is "\015\012". Under ASCII variants of Unix, that could usually be written as "\r\n", but under other systems, "\r\n" might at times be "\015\015\012", "\012\012\015", or something completely different. The standards specify writing "\015\012" to be conformant (be strict in what you provide), but they also recommend accepting a lone "\012" on input (be lenient in what you require). We haven't always been very good about that in the code in this manpage, but unless you're on a Mac from way back in its pre-Unix dark ages, you'll probably be ok.
Use Internet-domain sockets when you want to do client-server communication that might extend to machines outside of your own system.
Here's a sample TCP client using Internet-domain sockets:
#!/usr/bin/perl -w
use strict;
use Socket;
my ($remote, $port, $iaddr, $paddr, $proto, $line);
$remote = shift || "localhost";
$port = shift || 2345; # random port
if ($port =~ /\D/) { $port = getservbyname($port, "tcp") }
die "No port" unless $port;
$iaddr = inet_aton($remote) || die "no host: $remote";
$paddr = sockaddr_in($port, $iaddr);
$proto = getprotobyname("tcp");
socket(SOCK, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
connect(SOCK, $paddr) || die "connect: $!";
while ($line = <SOCK>) {
print $line;
close (SOCK) || die "close: $!";
And here's a corresponding server to go along with it. We'll leave the address as INADDR_ANY
so that the kernel can choose the appropriate interface on multihomed hosts. If you want sit on a particular interface (like the external side of a gateway or firewall machine), fill this in with your real address instead.
#!/usr/bin/perl -Tw
use strict;
BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
use Socket;
use Carp;
my $EOL = "\015\012";
sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
my $port = shift || 2345;
die "invalid port" unless if $port =~ /^ \d+ $/x;
my $proto = getprotobyname("tcp");
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
|| die "setsockopt: $!";
bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
listen(Server, SOMAXCONN) || die "listen: $!";
logmsg "server started on port $port";
my $paddr;
for ( ; $paddr = accept(Client, Server); close Client) {
my($port, $iaddr) = sockaddr_in($paddr);
my $name = gethostbyaddr($iaddr, AF_INET);
logmsg "connection from $name [",
inet_ntoa($iaddr), "]
at port $port";
print Client "Hello there, $name, it's now ",
scalar localtime(), $EOL;
And here's a multithreaded version. It's multithreaded in that like most typical servers, it spawns (fork()s) a slave server to handle the client request so that the master server can quickly go back to service a new client.
#!/usr/bin/perl -Tw
use strict;
BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
use Socket;
use Carp;
my $EOL = "\015\012";
sub spawn; # forward declaration
sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
my $port = shift || 2345;
die "invalid port" unless if $port =~ /^ \d+ $/x;
my $proto = getprotobyname("tcp");
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
|| die "setsockopt: $!";
bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
listen(Server, SOMAXCONN) || die "listen: $!";
logmsg "server started on port $port";
my $waitedpid = 0;
my $paddr;
use POSIX ":sys_wait_h";
use Errno;
sub REAPER {
local $!; # don't let waitpid() overwrite current error
while ((my $pid = waitpid(-1, WNOHANG)) > 0 && WIFEXITED($?)) {
logmsg "reaped $waitedpid" . ($? ? " with exit $?" : "");
$SIG{CHLD} = \&REAPER; # loathe SysV
while (1) {
$paddr = accept(Client, Server) || do {
# try again if accept() returned because got a signal
next if $!{EINTR};
die "accept: $!";
my ($port, $iaddr) = sockaddr_in($paddr);
my $name = gethostbyaddr($iaddr, AF_INET);
logmsg "connection from $name [",
"] at port $port";
spawn sub {
$| = 1;
print "Hello there, $name, it's now ", scalar localtime(), $EOL;
exec "/usr/games/fortune" # XXX: "wrong" line terminators
or confess "can't exec fortune: $!";
close Client;
sub spawn {
my $coderef = shift;
unless (@_ == 0 && $coderef && ref($coderef) eq "CODE") {
confess "usage: spawn CODEREF";
my $pid;
unless (defined($pid = fork())) {
logmsg "cannot fork: $!";
elsif ($pid) {
logmsg "begat $pid";
return; # I'm the parent
# else I'm the child -- go spawn
open(STDIN, "<&Client") || die "can't dup client to stdin";
open(STDOUT, ">&Client") || die "can't dup client to stdout";
## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr";
This server takes the trouble to clone off a child version via fork() for each incoming request. That way it can handle many requests at once, which you might not always want. Even if you don't fork(), the listen() will allow that many pending connections. Forking servers have to be particularly careful about cleaning up their dead children (called "zombies" in Unix parlance), because otherwise you'll quickly fill up your process table. The REAPER subroutine is used here to call waitpid() for any child processes that have finished, thereby ensuring that they terminate cleanly and don't join the ranks of the living dead.
Within the while loop we call accept() and check to see if it returns a false value. This would normally indicate a system error needs to be reported. However, the introduction of safe signals (see "Deferred Signals (Safe Signals)" above) in Perl 5.7.3 means that accept() might also be interrupted when the process receives a signal. This typically happens when one of the forked subprocesses exits and notifies the parent process with a CHLD signal.
If accept() is interrupted by a signal, $! will be set to EINTR. If this happens, we can safely continue to the next iteration of the loop and another call to accept(). It is important that your signal handling code not modify the value of $!, or else this test will likely fail. In the REAPER subroutine we create a local version of $! before calling waitpid(). When waitpid() sets $! to ECHILD as it inevitably does when it has no more children waiting, it updates the local copy and leaves the original unchanged.
You should use the -T flag to enable taint checking (see perlsec) even if we aren't running setuid or setgid. This is always a good idea for servers or any program run on behalf of someone else (like CGI scripts), because it lessens the chances that people from the outside will be able to compromise your system.
Let's look at another TCP client. This one connects to the TCP "time" service on a number of different machines and shows how far their clocks differ from the system on which it's being run:
#!/usr/bin/perl -w
use strict;
use Socket;
my $SECS_OF_70_YEARS = 2208988800;
sub ctime { scalar localtime(shift() || time()) }
my $iaddr = gethostbyname("localhost");
my $proto = getprotobyname("tcp");
my $port = getservbyname("time", "tcp");
my $paddr = sockaddr_in(0, $iaddr);
$| = 1;
printf "%-24s %8s %s\n", "localhost", 0, ctime();
foreach $host (@ARGV) {
printf "%-24s ", $host;
my $hisiaddr = inet_aton($host) || die "unknown host";
my $hispaddr = sockaddr_in($port, $hisiaddr);
socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
|| die "socket: $!";
connect(SOCKET, $hispaddr) || die "connect: $!";
my $rtime = pack("C4", ());
read(SOCKET, $rtime, 4);
my $histime = unpack("N", $rtime) - $SECS_OF_70_YEARS;
printf "%8d %s\n", $histime - time(), ctime($histime);
That's fine for Internet-domain clients and servers, but what about local communications? While you can use the same setup, sometimes you don't want to. Unix-domain sockets are local to the current host, and are often used internally to implement pipes. Unlike Internet domain sockets, Unix domain sockets can show up in the file system with an ls(1) listing.
% ls -l /dev/log
srw-rw-rw- 1 root 0 Oct 31 07:23 /dev/log
You can test for these with Perl's -S file test:
unless (-S "/dev/log") {
die "something's wicked with the log system";
Here's a sample Unix-domain client:
#!/usr/bin/perl -w
use Socket;
use strict;
my ($rendezvous, $line);
$rendezvous = shift || "catsock";
socket(SOCK, PF_UNIX, SOCK_STREAM, 0) || die "socket: $!";
connect(SOCK, sockaddr_un($rendezvous)) || die "connect: $!";
while (defined($line = <SOCK>)) {
print $line;
And here's a corresponding server. You don't have to worry about silly network terminators here because Unix domain sockets are guaranteed to be on the localhost, and thus everything works right.
#!/usr/bin/perl -Tw
use strict;
use Socket;
use Carp;
BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
sub spawn; # forward declaration
sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
my $NAME = "catsock";
my $uaddr = sockaddr_un($NAME);
my $proto = getprotobyname("tcp");
socket(Server, PF_UNIX, SOCK_STREAM, 0) || die "socket: $!";
bind (Server, $uaddr) || die "bind: $!";
listen(Server, SOMAXCONN) || die "listen: $!";
logmsg "server started on $NAME";
my $waitedpid;
use POSIX ":sys_wait_h";
sub REAPER {
my $child;
while (($waitedpid = waitpid(-1, WNOHANG)) > 0) {
logmsg "reaped $waitedpid" . ($? ? " with exit $?" : "");
$SIG{CHLD} = \&REAPER; # loathe SysV
for ( $waitedpid = 0;
accept(Client, Server) || $waitedpid;
$waitedpid = 0, close Client)
next if $waitedpid;
logmsg "connection on $NAME";
spawn sub {
print "Hello there, it's now ", scalar localtime(), "\n";
exec("/usr/games/fortune") || die "can't exec fortune: $!";
sub spawn {
my $coderef = shift();
unless (@_ == 0 && $coderef && ref($coderef) eq "CODE") {
confess "usage: spawn CODEREF";
my $pid;
unless (defined($pid = fork())) {
logmsg "cannot fork: $!";
elsif ($pid) {
logmsg "begat $pid";
return; # I'm the parent
else {
# I'm the child -- go spawn
open(STDIN, "<&Client") || die "can't dup client to stdin";
open(STDOUT, ">&Client") || die "can't dup client to stdout";
## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr";
As you see, it's remarkably similar to the Internet domain TCP server, so much so, in fact, that we've omitted several duplicate functions--spawn(), logmsg(), ctime(), and REAPER()--which are the same as in the other server.
So why would you ever want to use a Unix domain socket instead of a simpler named pipe? Because a named pipe doesn't give you sessions. You can't tell one process's data from another's. With socket programming, you get a separate session for each client; that's why accept() takes two arguments.
For example, let's say that you have a long-running database server daemon that you want folks to be able to access from the Web, but only if they go through a CGI interface. You'd have a small, simple CGI program that does whatever checks and logging you feel like, and then acts as a Unix-domain client and connects to your private server.
For those preferring a higher-level interface to socket programming, the IO::Socket module provides an object-oriented approach. IO::Socket has been included in the standard Perl distribution ever since Perl 5.004. If you're running an earlier version of Perl (in which case, how are you reading this manpage?), just fetch IO::Socket from CPAN, where you'll also find modules providing easy interfaces to the following systems: DNS, FTP, Ident (RFC 931), NIS and NISPlus, NNTP, Ping, POP3, SMTP, SNMP, SSLeay, Telnet, and Time--to name just a few.
Here's a client that creates a TCP connection to the "daytime" service at port 13 of the host name "localhost" and prints out everything that the server there cares to provide.
#!/usr/bin/perl -w
use IO::Socket;
$remote = IO::Socket::INET->new(
Proto => "tcp",
PeerAddr => "localhost",
PeerPort => "daytime(13)",
|| die "can't connect to daytime service on localhost";
while (<$remote>) { print }
When you run this program, you should get something back that looks like this:
Wed May 14 08:40:46 MDT 1997
Here are what those parameters to the new() constructor mean:
This is which protocol to use. In this case, the socket handle returned will be connected to a TCP socket, because we want a stream-oriented connection, that is, one that acts pretty much like a plain old file. Not all sockets are this of this type. For example, the UDP protocol can be used to make a datagram socket, used for message-passing.
This is the name or Internet address of the remote host the server is running on. We could have specified a longer name like "www.perl.com"
, or an address like "220.127.116.11"
. For demonstration purposes, we've used the special hostname "localhost"
, which should always mean the current machine you're running on. The corresponding Internet address for localhost is "127.0.0.1"
, if you'd rather use that.
This is the service name or port number we'd like to connect to. We could have gotten away with using just "daytime"
on systems with a well-configured system services file,[FOOTNOTE: The system services file is found in /etc/services under Unixy systems.] but here we've specified the port number (13) in parentheses. Using just the number would have also worked, but numeric literals make careful programmers nervous.
Notice how the return value from the new
constructor is used as a filehandle in the while
loop? That's what's called an indirect filehandle, a scalar variable containing a filehandle. You can use it the same way you would a normal filehandle. For example, you can read one line from it this way:
$line = <$handle>;
all remaining lines from is this way:
@lines = <$handle>;
and send a line of data to it this way:
print $handle "some data\n";
Here's a simple client that takes a remote host to fetch a document from, and then a list of files to get from that host. This is a more interesting client than the previous one because it first sends something to the server before fetching the server's response.
#!/usr/bin/perl -w
use IO::Socket;
unless (@ARGV > 1) { die "usage: $0 host url ..." }
$host = shift(@ARGV);
$BLANK = $EOL x 2;
for my $document (@ARGV) {
$remote = IO::Socket::INET->new( Proto => "tcp",
PeerAddr => $host,
PeerPort => "http(80)",
) || die "cannot connect to httpd on $host";
print $remote "GET $document HTTP/1.0" . $BLANK;
while ( <$remote> ) { print }
close $remote;
The web server handling the HTTP service is assumed to be at its standard port, number 80. If the server you're trying to connect to is at a different port, like 1080 or 8080, you should specify it as the named-parameter pair, PeerPort => 8080
. The autoflush
method is used on the socket because otherwise the system would buffer up the output we sent it. (If you're on a prehistoric Mac, you'll also need to change every "\n"
in your code that sends data over the network to be a "\015\012"
Connecting to the server is only the first part of the process: once you have the connection, you have to use the server's language. Each server on the network has its own little command language that it expects as input. The string that we send to the server starting with "GET" is in HTTP syntax. In this case, we simply request each specified document. Yes, we really are making a new connection for each document, even though it's the same host. That's the way you always used to have to speak HTTP. Recent versions of web browsers may request that the remote server leave the connection open a little while, but the server doesn't have to honor such a request.
Here's an example of running that program, which we'll call webget:
% webget www.perl.com /guanaco.html
HTTP/1.1 404 File Not Found
Date: Thu, 08 May 1997 18:02:32 GMT
Server: Apache/1.2b6
Connection: close
Content-type: text/html
<HEAD><TITLE>404 File Not Found</TITLE></HEAD>
<BODY><H1>File Not Found</H1>
The requested URL /guanaco.html was not found on this server.<P>
Ok, so that's not very interesting, because it didn't find that particular document. But a long response wouldn't have fit on this page.
For a more featureful version of this program, you should look to the lwp-request program included with the LWP modules from CPAN.
Well, that's all fine if you want to send one command and get one answer, but what about setting up something fully interactive, somewhat like the way telnet works? That way you can type a line, get the answer, type a line, get the answer, etc.
This client is more complicated than the two we've done so far, but if you're on a system that supports the powerful fork
call, the solution isn't that rough. Once you've made the connection to whatever service you'd like to chat with, call fork
to clone your process. Each of these two identical process has a very simple job to do: the parent copies everything from the socket to standard output, while the child simultaneously copies everything from standard input to the socket. To accomplish the same thing using just one process would be much harder, because it's easier to code two processes to do one thing than it is to code one process to do two things. (This keep-it-simple principle a cornerstones of the Unix philosophy, and good software engineering as well, which is probably why it's spread to other systems.)
Here's the code:
#!/usr/bin/perl -w
use strict;
use IO::Socket;
my ($host, $port, $kidpid, $handle, $line);
unless (@ARGV == 2) { die "usage: $0 host port" }
($host, $port) = @ARGV;
# create a tcp connection to the specified host and port
$handle = IO::Socket::INET->new(Proto => "tcp",
PeerAddr => $host,
PeerPort => $port)
|| die "can't connect to port $port on $host: $!";
$handle->autoflush(1); # so output gets there right away
print STDERR "[Connected to $host:$port]\n";
# split the program into two processes, identical twins
die "can't fork: $!" unless defined($kidpid = fork());
# the if{} block runs only in the parent process
if ($kidpid) {
# copy the socket to standard output
while (defined ($line = <$handle>)) {
print STDOUT $line;
kill("TERM", $kidpid); # send SIGTERM to child
# the else{} block runs only in the child process
else {
# copy standard input to the socket
while (defined ($line = <STDIN>)) {
print $handle $line;
exit(0); # just in case
The kill
function in the parent's if
block is there to send a signal to our child process, currently running in the else
block, as soon as the remote server has closed its end of the connection.
If the remote server sends data a byte at time, and you need that data immediately without waiting for a newline (which might not happen), you may wish to replace the while
loop in the parent with the following:
my $byte;
while (sysread($handle, $byte, 1) == 1) {
print STDOUT $byte;
Making a system call for each byte you want to read is not very efficient (to put it mildly) but is the simplest to explain and works reasonably well.
As always, setting up a server is little bit more involved than running a client. The model is that the server creates a special kind of socket that does nothing but listen on a particular port for incoming connections. It does this by calling the IO::Socket::INET->new()
method with slightly different arguments than the client did.
This is which protocol to use. Like our clients, we'll still specify "tcp"
We specify a local port in the LocalPort
argument, which we didn't do for the client. This is service name or port number for which you want to be the server. (Under Unix, ports under 1024 are restricted to the superuser.) In our sample, we'll use port 9000, but you can use any port that's not currently in use on your system. If you try to use one already in used, you'll get an "Address already in use" message. Under Unix, the netstat -a
command will show which services current have servers.
The Listen
parameter is set to the maximum number of pending connections we can accept until we turn away incoming clients. Think of it as a call-waiting queue for your telephone. The low-level Socket module has a special symbol for the system maximum, which is SOMAXCONN.
The Reuse
parameter is needed so that we restart our server manually without waiting a few minutes to allow system buffers to clear out.
Once the generic server socket has been created using the parameters listed above, the server then waits for a new client to connect to it. The server blocks in the accept
method, which eventually accepts a bidirectional connection from the remote client. (Make sure to autoflush this handle to circumvent buffering.)
To add to user-friendliness, our server prompts the user for commands. Most servers don't do this. Because of the prompt without a newline, you'll have to use the sysread
variant of the interactive client above.
This server accepts one of five different commands, sending output back to the client. Unlike most network servers, this one handles only one incoming client at a time. Multithreaded servers are covered in Chapter 16 of the Camel.
Here's the code. We'll
#!/usr/bin/perl -w
use IO::Socket;
use Net::hostent; # for OOish version of gethostbyaddr
$PORT = 9000; # pick something not in use
$server = IO::Socket::INET->new( Proto => "tcp",
LocalPort => $PORT,
Listen => SOMAXCONN,
Reuse => 1);
die "can't setup server" unless $server;
print "[Server $0 accepting clients]\n";
while ($client = $server->accept()) {
print $client "Welcome to $0; type help for command list.\n";
$hostinfo = gethostbyaddr($client->peeraddr);
printf "[Connect from %s]\n", $hostinfo ? $hostinfo->name : $client->peerhost;
print $client "Command? ";
while ( <$client>) {
next unless /\S/; # blank line
if (/quit|exit/i) { last }
elsif (/date|time/i) { printf $client "%s\n", scalar localtime() }
elsif (/who/i ) { print $client `who 2>&1` }
elsif (/cookie/i ) { print $client `/usr/games/fortune 2>&1` }
elsif (/motd/i ) { print $client `cat /etc/motd 2>&1` }
else {
print $client "Commands: quit date who cookie motd\n";
} continue {
print $client "Command? ";
close $client;
Another kind of client-server setup is one that uses not connections, but messages. UDP communications involve much lower overhead but also provide less reliability, as there are no promises that messages will arrive at all, let alone in order and unmangled. Still, UDP offers some advantages over TCP, including being able to "broadcast" or "multicast" to a whole bunch of destination hosts at once (usually on your local subnet). If you find yourself overly concerned about reliability and start building checks into your message system, then you probably should use just TCP to start with.
UDP datagrams are not a bytestream and should not be treated as such. This makes using I/O mechanisms with internal buffering like stdio (i.e. print() and friends) especially cumbersome. Use syswrite(), or better send(), like in the example below.
Here's a UDP program similar to the sample Internet TCP client given earlier. However, instead of checking one host at a time, the UDP version will check many of them asynchronously by simulating a multicast and then using select() to do a timed-out wait for I/O. To do something similar with TCP, you'd have to use a different socket handle for each host.
#!/usr/bin/perl -w
use strict;
use Socket;
use Sys::Hostname;
my ( $count, $hisiaddr, $hispaddr, $histime,
$host, $iaddr, $paddr, $port, $proto,
$rin, $rout, $rtime, $SECS_OF_70_YEARS);
$iaddr = gethostbyname(hostname());
$proto = getprotobyname("udp");
$port = getservbyname("time", "udp");
$paddr = sockaddr_in(0, $iaddr); # 0 means let kernel pick
socket(SOCKET, PF_INET, SOCK_DGRAM, $proto) || die "socket: $!";
bind(SOCKET, $paddr) || die "bind: $!";
$| = 1;
printf "%-12s %8s %s\n", "localhost", 0, scalar localtime();
$count = 0;
for $host (@ARGV) {
$hisiaddr = inet_aton($host) || die "unknown host";
$hispaddr = sockaddr_in($port, $hisiaddr);
defined(send(SOCKET, 0, 0, $hispaddr)) || die "send $host: $!";
$rin = "";
vec($rin, fileno(SOCKET), 1) = 1;
# timeout after 10.0 seconds
while ($count && select($rout = $rin, undef, undef, 10.0)) {
$rtime = "";
$hispaddr = recv(SOCKET, $rtime, 4, 0) || die "recv: $!";
($port, $hisiaddr) = sockaddr_in($hispaddr);
$host = gethostbyaddr($hisiaddr, AF_INET);
$histime = unpack("N", $rtime) - $SECS_OF_70_YEARS;
printf "%-12s ", $host;
printf "%8d %s\n", $histime - time(), scalar localtime($histime);
This example does not include any retries and may consequently fail to contact a reachable host. The most prominent reason for this is congestion of the queues on the sending host if the number of hosts to contact is sufficiently large.
While System V IPC isn't so widely used as sockets, it still has some interesting uses. However, you cannot use SysV IPC or Berkeley mmap() to have a variable shared amongst several processes. That's because Perl would reallocate your string when you weren't wanting it to. You might look into the IPC::Shareable
or threads::shared
modules for that.
Here's a small example showing shared memory usage.
use IPC::SysV qw(IPC_PRIVATE IPC_RMID S_IRUSR S_IWUSR);
$size = 2000;
$id = shmget(IPC_PRIVATE, $size, S_IRUSR | S_IWUSR);
defined($id) || die "shmget: $!";
print "shm key $id\n";
$message = "Message #1";
shmwrite($id, $message, 0, 60) || die "shmwrite: $!";
print "wrote: '$message'\n";
shmread($id, $buff, 0, 60) || die "shmread: $!";
print "read : '$buff'\n";
# the buffer of shmread is zero-character end-padded.
substr($buff, index($buff, "\0")) = "":
print "un" unless $buff eq $message;
print "swell\n";
print "deleting shm $id\n";
shmctl($id, IPC_RMID, 0) || die "shmctl: $!";
Here's an example of a semaphore:
use IPC::SysV qw(IPC_CREAT);
$id = semget($IPC_KEY, 10, 0666 | IPC_CREAT);
defined($id) || die "shmget: $!";
print "shm key $id\n";
Put this code in a separate file to be run in more than one process. Call the file take:
# create a semaphore
$id = semget($IPC_KEY, 0, 0);
defined($id) || die "shmget: $!";
$semnum = 0;
$semflag = 0;
# "take" semaphore
# wait for semaphore to be zero
$semop = 0;
$opstring1 = pack("s!s!s!", $semnum, $semop, $semflag);
# Increment the semaphore count
$semop = 1;
$opstring2 = pack("s!s!s!", $semnum, $semop, $semflag);
$opstring = $opstring1 . $opstring2;
semop($id, $opstring) || die "semop: $!";
Put this code in a separate file to be run in more than one process. Call this file give:
# "give" the semaphore
# run this in the original process and you will see
# that the second process continues
$id = semget($IPC_KEY, 0, 0);
die unless defined($id);
$semnum = 0;
$semflag = 0;
# Decrement the semaphore count
$semop = -1;
$opstring = pack("s!s!s!", $semnum, $semop, $semflag);
semop($id, $opstring) || die "semop: $!";
The SysV IPC code above was written long ago, and it's definitely clunky looking. For a more modern look, see the IPC::SysV module which is included with Perl starting from Perl 5.005.
A small example demonstrating SysV message queues:
use IPC::SysV qw(IPC_PRIVATE IPC_RMID IPC_CREAT S_IRUSR S_IWUSR);
my $id = msgget(IPC_PRIVATE, IPC_CREAT | S_IRUSR | S_IWUSR);
defined($id) || die "msgget failed: $!";
my $sent = "message";
my $type_sent = 1234;
msgsnd($id, pack("l! a*", $type_sent, $sent), 0)
|| die "msgsnd failed: $!";
msgrcv($id, my $rcvd_buf, 60, 0, 0)
|| die "msgrcv failed: $!";
my($type_rcvd, $rcvd) = unpack("l! a*", $rcvd_buf);
if ($rcvd eq $sent) {
print "okay\n";
} else {
print "not okay\n";
msgctl($id, IPC_RMID, 0) || die "msgctl failed: $!\n";
Most of these routines quietly but politely return undef
when they fail instead of causing your program to die right then and there due to an uncaught exception. (Actually, some of the new Socket conversion functions do croak() on bad arguments.) It is therefore essential to check return values from these functions. Always begin your socket programs this way for optimal success, and don't forget to add the -T taint-checking flag to the #!
line for servers:
#!/usr/bin/perl -Tw
use strict;
use sigtrap;
use Socket;
These routines all create system-specific portability problems. As noted elsewhere, Perl is at the mercy of your C libraries for much of its system behavior. It's probably safest to assume broken SysV semantics for signals and to stick with simple TCP and UDP socket operations; e.g., don't try to pass open file descriptors over a local UDP datagram socket if you want your code to stand a chance of being portable.
Tom Christiansen, with occasional vestiges of Larry Wall's original version and suggestions from the Perl Porters.
There's a lot more to networking than this, but this should get you started.
For intrepid programmers, the indispensable textbook is Unix Network Programming, 2nd Edition, Volume 1 by W. Richard Stevens (published by Prentice-Hall). Most books on networking address the subject from the perspective of a C programmer; translation to Perl is left as an exercise for the reader.
The IO::Socket(3) manpage describes the object library, and the Socket(3) manpage describes the low-level interface to sockets. Besides the obvious functions in perlfunc, you should also check out the modules file at your nearest CPAN site, especially http://www.cpan.org/modules/00modlist.long.html#ID5_Networking_. See perlmodlib or best yet, the Perl FAQ for a description of what CPAN is and where to get it if the previous link doesn't work for you.
Section 5 of CPAN's modules file is devoted to "Networking, Device Control (modems), and Interprocess Communication", and contains numerous unbundled modules numerous networking modules, Chat and Expect operations, CGI programming, DCE, FTP, IPC, NNTP, Proxy, Ptty, RPC, SNMP, SMTP, Telnet, Threads, and ToolTalk--to name just a few.


text:
Ekipat -i-priqteli-radio-sinai gets the job done!
About UsWe are reliable professionals with over 30 years of experience. We listen to our customers and work with them to address their needs through innovative solutions. ServicesYou name it and we can provide it. With an experienced staff working around the clock, you can be sure we will get the job done and get it done right. |
We started with just two employees, working out of a small room. All these years later, we have over 40 employees, but our passion and dedication remain strong. Working with us, you will find we still stay true to our roots.
"This is sample testimonial from a sample source." -- Sample Client, Location
"This is another sample testimonial from another sample source." -- Sample Client, Location


text:
Defining a global glossary
Only administrators, and other users with the capability site:doanything allowed, can define a glossary to be global.
Any course may contain a global glossary (but particularly the front page).
The difference to a normal local glossary is that the entries are used to create automatic links throughout the whole site (and not just in the same course the glossary belongs to).