To catch the start of a sequence from a file
===


I have a text file which goes like this :

          125
          126
          127    {
          566
          567
          568
          569       # blah bkah
          570    {  #blah blah
          700
          701    {

The numbers are left aligned and the pattern is always the same in the sense increasing and a curly braces at the end .I need to catch just the starting number .The braces are always found and  limited to the sequence end .The start of the file is as shown starting with '125'.

In short I need : 
    
          125
          566
          700

What I have come up with :

          grep -A1 '{' | grep -v '{' | grep -oE '(^[0-9]+?)'

but this omits '125' but I overcame by appending a newline at the head and inserting a `{` .

I hope this cah be reduced into a single regex.

Suggestions and better algorithms are welcome

