matching an array of alternates

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: matching an array of alternates by btrott (Parson) on Jun 23, 2000 at 23:17 UTC
Build a regular expression that will match those countries, then scan through the file and check each line against it: `my $regex = join '\|', @latin_am; while (<>) { print $1 if /$regex/; }` [download] This reads from STDIN, so invoke it like this: `% foo.pl file` [download]	[reply] [d/l] [select]
RE: Re: matching an array of alternates by Zoogie (Curate) on Jun 23, 2000 at 23:54 UTC
Just wanted to point out that if the file you're searching has a lot of lines, you can gain some speed by adding the "o" option to the regex; i.e.: `print $1 if /$regex/o;` [download] This way, the regular expression only has to be compiled once. - Zoogie	[reply] [d/l]
Re: matching an array of alternates by takshaka (Friar) on Jun 24, 2000 at 07:23 UTC
The pipe-joined monolithic regex isn't terribly efficient. The qr// approach described in perlfaq6 (that is, versions of perlfaq6 that ship with Perl 5.005 or later, but not the one on this site) is much faster. `my @regexes = map { qr/\Q$_/ } @latin_am; while (<>) { for my $regex (@regexes) { if ($_ =~ $regex) { print; last; } } }` [download]	[reply] [d/l]
Re: matching an array of alternates by perlmonkey (Hermit) on Jun 24, 2000 at 02:27 UTC
This should do the trick: `@latin_am=("Ecuador","Mexico"); $regex = join ("\|", @latin_am); open( FILE, 'input.txt' ) or die "input.txt: $!"; @lines = grep { /$regex/o } <FILE>;` [download] @lines will hold all the lines of the file 'input.txt' that match any of the phrases in @latin_am	[reply] [d/l]