in reply to How can I print three lines before pattern match?

Try this... 
#!/usr/bin/perl

use strict;

my @file = <DATA>;

for my $i (0 .. $#file) {
    if ( $file[$i] =~ /pattern/ ) {
        print "$file[$_]" for ($i-3 .. $i-1);
    }
}

__DATA__
log info line yada yada 0
log info line yada yada 1
log info line yada yada 2
log info line yada yada 3
log info line (pattern) 4
log info line yada yada 5

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Re^2: How can I print three lines before pattern match?
by ikegami (Patriarch) on Aug 14, 2009 at 02:50 UTC
    That doesn't work if the pattern is found in the first three lines. (And what's with the quotes around a variable?) Change 
    print "$file[$_]" for ($i-3 .. $i-1);

    [download]
    to 
    print $file[$_] for grep $_ >= 0, $i-3 .. $i-1;

    [download]
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      Thanks ikegami. Those are good points.
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Re^2: How can I print three lines before pattern match?
by neurotoxx (Novice) on Aug 14, 2009 at 02:34 UTC

    Not sure I understand this:

    for my $i (0 .. $#file)

    Is the #file a reference to my data file?

    So then, for my $i (0 .. $data.log)

    Thank you.

    Sorry for my ignorance.

[reply]
      Is the #file a reference to my data file?

      No, not directly. Instead, the idea presented was to capture the whole file in @file: 

      my @file = <DATA>;

      [download]

      In your case, it would be <INFILE> instead of <DATA>. (<DATA> is a special file handle, starting after the special tag __DATA__ in the script, but otherwise pretty much a normal-behaving file handle.)

      The $# in front of an array identifier means "the last index of" that array.

      Perhaps better is to keep the last three lines in a fifo: 

      open(INFILE, "< file.log")
         or die "Cant open file : $!";

open(OUT, "> results.txt")
         or die "Cant open new file : $!";

$pattern = "Error code 2";

my @file;
while (<INFILE>) {
    print OUT @file if (/$pattern/ and @file);
    push @file, $_;           # push on the current line
    shift @file while (@file > 3); # shorten to 3 elements
}

close INFILE;
close OUT;

      [download]

      Don't forget warnings and strict.

      -QM
      --
      Quantum Mechanics: The dreams stuff is made of

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      $#file is the index of the last element in the array @file.
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