The easiest way would be not to go back: Just search for ipconfig and sub in parallel. If you find a sub, just store the related function-name (as this is the function you are currently in). And if you find an ipconfig, just take that name.

update begin You could also do a two-pass-reading: in the first pass you would read all functions that are defined in your file, and store their name and the line where they start. In the second pass you would search for your keyword, check the line where it occurs and use this to determine the function name. update end

You will of course still need to handle the case of your keywords occuring in strings, comments and so on...

One approach is to just read the whole file into a scalar, search for the desired command, then extract everything up to that command into a second string, and search for the last function definition inside that second string.

Another approach is to read the file line by line, and when a match is found, open a second handle to that file, this time reading backwards (either File::ReadBackwards or PerlIO::reverse), seek to the position of the find, and then read (backwards) until the function definition is found.

A third approach is to read the file in function chunks straight away, and then search each chunk for the commands.

#!/usr/bin/perl

use warnings;
use strict;
use 5.10.0;

my $search_term = 'ipconfig';
my %subs;
my $name;

while ( my $line = <DATA> ){
    if ( $line =~ /^sub\s+/ ){
        $name = (split /\s+/, $line)[1];
        $subs{ $name } = 0;
        next;
    }
    $subs{ $name } = 1 if $line =~ /$search_term/;
}

while ( my ($k,$v) = each %subs ){
    say "sub $k calls $search_term" if $v;
}
__DATA__

sub one {
    #one
    #two
    #three
    #ipconfig
    #four
}
sub two {
    #hello
    #there
    #wonderful
    #world
}
sub three {
    #ifconfig
    #ipconfig
    #nmap -sS -P0 localhost
    #tcpdump -n -i re0 -s 0 -w a.file
[download]

EDIT: made it a bit more generic and descriptive

Thanks for the perl module stevieb, unfortunately we are locked down as to what perl versions we can use. However you snipped of code above is exactly what I need :-D I just have to read up on hashes now to understand what you are doing :)

I was bored for a couple hours earlier today, so I wrote a module for this and upped it to the CPAN :)

Steve