Hi Perlmonks,

Below is a code i'm testing. I am a beginner at Perl and saw that the $` special variable refers to the string preceding a match. I wanted to try using it to print a line previous to a matched string.
If this is not possible then any advice on how to print a string previous to a matched string would be very welcome. The problem is I get the following warning and can't figure out how to fix it

Use of uninitialized value in pattern match (m//) at test.pl line 9, <FH> line 1.
Use of uninitialized value in pattern match (m//) at test.pl line 9, <FH> line 2.
Use of uninitialized value in pattern match (m//) at test.pl line 9, <FH> line 3.
Use of uninitialized value in pattern match (m//) at test.pl line 9, <FH> line 4.
Use of uninitialized value in pattern match (m//) at test.pl line 9, <FH> line 5.

the contents of the file are (i'm only using this file to test the script, normally these files could have several strings of letters with each having a title line beginning with >)

>random_seq 
atggtccgtgatcagcatcctttggggaatccacatttattcggaccacctccggattcgtcagcatgac
+agctggtcgugguuuaguaugatgtgatgcgatcatgtacatcaggatttaggaggccctccactgcat
+cgtcgactagacgatcagttagggaaaacgtaugguugugatggtacatgacggaccacacgccgactt
+agcatttgttacagtagcgtgattgacatguuguuggug

[download]


I want to test the string of letters for a motif and if found print the line beginning with '>' (i.e. the line/string before the match). finally, here's the code


<code> #!usr/bin/perl use strict;use warnings;

my $filename = $ARGV[0];
open (FH, $filename) || die "Cannot open file\n";

while (<FH>)
{
if (my $line =~ m/A-Za-z/)
{
print $`;
}
}
close FH;
<code>
would appreciate any help you have to offer

GrandFather added code tags to break long line.

In reply to Special Variable help by utterlyconfused

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.