title: regular expressions in tcsh shell script
body: <p>I have a shell script in tcsh to which I pass an argument, the length of which can vary. The possible values of the argument are the letters -c,s,i,q,a. and also a combination of these letters. (e.g: cs,si,ca,iq,qa,csq,acs,csia ..etc). The order of the letters does not matter. 
  My problem is to check the argument for any character other than these 5 and if any of the valid character appear more than one time (zero time is ok). The script should check both the conditions and throw an error. Is there any regular expression that I can use with if statement for this purpose?</p>