#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use diagnostics;
undef $/;

my $file = "test.txt";
open INFILE, "<$file" or die "cant open file: $!\n";
my @arr = <INFILE>;
close INFILE;
foreach my $filepieces (@arr) {
    my @matches = $1 if ($filepieces =~ /alpha\|(.*?)\|/smg);
    if(@matches) {
        foreach my $match (@matches) {
            print "match: $match\n";
        }
    }
}
[download]

alpha|beta|alpha|theta|alpha|gamma|alpha|episilon
[download]

This will:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use diagnostics;

undef $/;
my $text = <DATA>;

my @matches;
if (@matches = $text =~ /alpha\|([^|]+)\|/smg) {
    foreach my $match (@matches) {
        print "match: $match\n";
    }
}

__DATA__
alpha|beta|alpha|theta|alpha|gamma|alpha|episilon
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Output:

match: beta
match: theta
match: gamma
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Or you could dispense with loading data into the array at all (unless you need it for later):

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use diagnostics;

undef $/;
my $text = <DATA>;

while ($text =~ /alpha\|([^|]+)\|/smg) {
    print "match: $1\n";
}

__DATA__
alpha|beta|alpha|theta|alpha|gamma|alpha|episilon
[download]


All dogma is stupid.

Never do
my $var = ... if ...;,
my $var = ... unless ...;,
my $var = ... for ...;,
my $var = ... foreach ...; or
my $var = ... while ...;

Split them into two statements, like
my $var; $var = ... if ...;.

Update: Well, this is bothering me. I can't remember why, and I can't find an example where the above fails.

Update: diotalevi, which I believe has a knowledge of Perl guts, mentions: "my() has a runtime effect. You *always* (unless you're doing something freakish) want that to happen. The my $var STATEMENT-MODIFIER allows the runtime part of my() to potentially not happen." In other words, it sounds like doing any of the above leaves perl in an unstable state.

not following here?

my $var = $1 if ($filecontents =~ /SOME_REGEX(.*?)$/g);
if($var) {
   ... proceed w/ usage of $var
}
[download]

why pre-declare, then use?