zcat working in command line but not in perl script - perl

Question

Here is a part of my script:
foreach $i ( #contact_list ) {
print "$i\n";
$e = "zcat $file_list2| grep $i";
print "$e\n";
$f = qx($e);
print "$f";
}
$e prints properly but $f gives a blank line even when $file_list2 has a match for $i.
Can anyone tell me why?

Answer 1

Always is better to use Perl's grep instead of using pipe :
#lines = `zcat $file_list2`; # move output of zcat to array
die('zcat error') if ($?); # will exit script with error if zcat is problem
# chomp(#lines) # this will remove "\n" from each line
foreach $i ( #contact_list ) {
print "$i\n";
#ar = grep (/$i/, #lines);
print #ar;
# print join("\n",#ar)."\n"; # in case of using chomp
}
Best solution is not calling zcat, but using zlib library :
http://perldoc.perl.org/IO/Zlib.html
use IO::Zlib;
# ....
# place your defiiniton of $file_list2 and #contact list here.
# ...
$fh = new IO::Zlib; $fh->open($file_list2, "rb")
or die("Cannot open $file_list2");
#lines = <$fh>;
$fh->close;
#chomp(#lines); #remove "\n" symbols from lines
foreach $i ( #contact_list ) {
print "$i\n";
#ar = grep (/$i/, #lines);
print (#ar);
# print join("\n",#ar)."\n"; #in case of using chomp
}

Answer 2

Your question leaves us guessing about many things, but a better overall approach would seem to be opening the file just once, and processing each line in Perl itself.
open(F, "zcat $file_list |") or die "$0: could not zcat: $!\n";
LINE:
while (<F>) {
######## FIXME: this could be optimized a great deal still
foreach my $i (#contact_list) {
if (m/$i/) {
print $_;
next LINE;
}
}
}
close (F);
If you want to squeeze out more from the inner loop, compile the regexes from #contact_list into a separate array before the loop, or perhaps combine them into a single regex if all you care about is whether one of them matched. If, on the other hand, you want to print all matches for one pattern only at the end when you know what they are, collect matches into one array per search expression, then loop them and print when you have grepped the whole set of input files.
Your problem is not reproducible without information about what's in $i, but I can guess that it contains some shell metacharacter which causes it to be processed by the shell before the grep runs.