Perl IF statement not matching variables in REGEX - perl

Question

my $pointer = 0;
foreach (#new1)
{
my $test = $_;
foreach (#chk)
{
my $check = $_;
chomp $check;
delete($new1[$pointer]) if ($test =~ /^$check/i);
}
$pointer++;
}
The if statement never matches the fact that many entries in the #new1 array do contain $check at the start of the array element (88 at least).
I am not sure it is the nested loop that is causing the problem because if i try this it also fails to match:
foreach (#chk)
{
#final = (grep /^$_/, #new1);
}
#final is empty but I know at least 88 entires for $_ are in #new1.
I wrote this code on a machine running Windows ActivePerl 5.14.2 and the top code works. I then (using a copy of #new1) compare the two and remove any duplicates (also works on 5.14.2). I did try to negate the if match but that seemed to wipe out the #new1 array (so that I didn't need to do a hash compare).
When I try to run this code on a Linux RedHat box with Perl 5.8.0 it seems to struggle with the variable matching in the REGEX. If I hard code the REGEX with an example I know is in #new1 the match works and in the first code the entry is deleted (in the second one value is inserted in #final).
The #chk array is a listing file on the web server and the #new1 array is created by opening two log files on the web server and then pushing one into the other.
I had even gone to the trouble of printing out $test and $check in each loop iteration and manually checking to see if any of the the values did match and some of them do.
It has had me baffled for days now and I have had to throw the towel in and ask for help, any ideas?

Answer 1

As tested by user1568538, the solution was to replace
chomp $check;
with
$check =~ s/\r\n//g;
to remove Windows-style line endings from the variable.
Since chomp removes the contents of the input record separator $/ from the end of its argument, you could also change its value:
my $pointer = 0;
foreach (#new1)
{
my $test = $_;
foreach (#chk)
{
local $/="\r\n";
my $check = $_;
chomp $check;
delete($new1[$pointer]) if ($test =~ /^$_/i);
}
$pointer++;
}
However, since $/ also affects other operations (such as reading from a file handle), perhaps it is safest to avoid changing $/ unless you are sure if it is safe. Here I limit the change to the foreach loop where the chomp occurs.

Answer 2

No knowing what your input data looks like, using \Q might help:
if ($test =~ /^\Q$check/i);
See quotemeta.

Answer 3

It is not clear what you are trying to do. However, you may be trying to only get those elements for which there is no match or vice versa. Adapt the code below for your needs
#!/usr/bin/perl
use strict; use warnings;
my #item = qw(...); # your #new?
my #check = qw(...); # your #chk?
my #match;
my #nomatch;
ITEM:
foreach my $item (#item) {
CHECK:
foreach my $check (#check) {
# uncomment this if $check should not be interpreted as a pattern,
# but as literal characters:
# $item = '\Q' . $item;
if ($item =~ /^$check/) {
push #match, $item;
next ITEM; # there was a match, so this $item is burnt
# we don't need to test against other $checks.
}
}
# there was no match, so lets store it:
push #nomatch, $item.
}
print "matched $_\n" for #matched;
print "didn't match $_" for #nomatch;
Your code is somewhat difficult to read. Let me tell you what this
foreach (#chk) {
#final = (grep /^$_/, #new1);
}
does: It is roughly equivalent to
my #final = ();
foreach my $check (#chk) {
#final = grep /^$check/, #new1;
}
which is equivalent to
my #final = ();
foreach my $check (#chk) {
# #final = grep /^$check/, #new1;
#final = ();
foreach (#new) {
if (/^$check/) {
push #final, $_;
last;
}
}
}
So your #final array gets reset, possibly emptied.