Suggestions above do work just fine. I made one small addition, if your are on Perl 5.10 you can use the // operator. This sets a default value of "no match" as shown below if say $4 is undefined. There aren't any write statements below so you shouldn't get your reported error anymore. You will however start getting print of undefined value warnings which the "//" avoids.

#!/usr/bin/perl -w
use strict;

open (FILE,"abc345.txt") or die $!;

       while (<FILE>){
       $_ =~ /((^Query = .*)|(^\>.*)|(Length = .*))/i;
       print  $1 // "no match", "\n";
       print  $2 // "no match", "\n";
       print  $3 // "no match", "\n";
       print  $4 // "no match", "\n";   
       }

close (FILE) ;

[download]
For data line of: Query = 345, prints:
Query = 345 
Query = 345 
no match
no match

[download]
Update: Had wrong file handle above in "while (<FILE>)". I used <DATA> to test my code and that didn't get corrected in the original post. Anyway the above code does run on my AS Perl 5.10.X machine. I had thought that perhaps something weird was happening with the "=" as that does have significance in a regex, but only in combination with for example "?=". Result is that you do not have to "escape" the = sign. Above code is fine. An escape "\" is required for these characters:  {}[]()^$.|*+?\

In reply to Re^3: add new lines to output. by Marshall
in thread add new lines to output. by shaludr

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.