Perl input file string match

Question

I'm very new to Perl and am attempting to write a script to search through a file and check/match a number of strings from an additional input file. Here's what I have as of right now:

#! /css/dvltools/localperl/bin/perl

open CUMRT603, "CUMRT603";

my $meter, $my_cur_line;
while ( <CUMRT603> )
{
        $my_cur_line = $_;
        chomp $my_cur_line;

        open METER_LIST, "mlist";
        while ( <METER_LIST> )
        {
                $meter = $_;
                if ( $my_cur_line =~ /"$meter"/ )
                {
                        print "Found $meter on $my_cur_line";
                }
        }

        close METER_LIST;
}

Basically, I'm searching CUMRT603 for any string found in list (mlist). I can't get it to show any string matches (There should be at least one). Any advice on syntax, structure, etc. is apperciated. This is bascially my first perl script.

You don't have to re-read the second file for each line of the first one - it's terribly inefficient. And you don't have to use Perl here, as you can find file intersections with grep -Fx file1 file2 bash command. — raina77ow
– raina77ow, Commented Dec 6, 2012 at 15:10

TLP · Accepted Answer · 2012-12-06 15:48:01Z

2

You lack a chomp on your $meter input, so presumably it can never match the chomped $my_cur_line variable.

Moreover, those double quotes in your regex will be interpreted literally, so if $meter is foo, it will try to match "foo", which I am not sure is what you want.

Also, you might wish to prevent meta characters from being used in your matched text, which can be done with quotemeta or \Q ... \E.

So, in short, your code should probably be:

chomp $meter;
if ( $my_cur_line =~ /\Q$meter\E/ )

You also really should use

use strict;
use warnings;

The short learning curve more than weighs up for the saved time in debugging.

edited Dec 6, 2012 at 15:48

answered Dec 6, 2012 at 15:24

TLP

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4 Comments

TLP Over a year ago

@TyC Well, for example, if you have the string foo?, that would in a regex mean "fo followed by an optional o", whereas you might mean "foo followed by a question mark". By escaping the meta characters, you cause them to be interpreted literally.

TyC Over a year ago

So you're explicitly saying the variable $meter not '$meter'?

TLP Over a year ago

I am saying that /"$meter"/ matches "foo", not foo. You don't use quotes in regexes unless you are looking for literal quotes.

TyC Over a year ago

It was indeed the quotes causing the match not to work. Thanks for the help.

Andy Lester · Accepted Answer · 2012-12-06 15:15:43Z

2

You need to tell us what "can't get it to work properly" means. What happens when you run it? What results do you get? What results did you expect?

One big problem is that you're not checking the result of your open. If the file can't be opened, then nothing else will work correctly. You'll get no results from <CURMT603>, and those you'll exit the outer while loop immediately. Same goes with the open of METER_LIST.

Also, you need to put

use warnings;
use strict;

at the top of your program to help you catch typos. Otherwise, Perl will let things slide because it assumes you know better, but that's not the case here.

Third, use the three-argument form of open and use lexical filehandles.

Fourth, you can read directly into variables. You don't have to assign from $_.

So here's a quick rewrite of what you have.

use warnings;
use strict;

open( my $cur_file, '<', 'CURMT603' ) or die "Unable to open CURMT603: $!";

while ( my $cur_line = <$cur_file> ) {
    chomp $cur_line;
    open( my $meter_file, '<', 'mlist' ) or die "Can't open meter file: $!";
    while ( my $meter = <$meter_file> ) {
        if ( $my_cur_line =~ /"$meter"/ ) {
            print "Found $meter on $my_cur_line\n";
        }
    }
    close $meter_file;
}
close $cur_file;

So, try that, now with the new filehandling and error checking, and see how that goes. I'm betting that adding the error checking on the file opens will turn up your problem.

Final note: You don't need to reread the same mlist file over and over for each time through the CURMT603 file, but that's an optimization for another time.

answered Dec 6, 2012 at 15:15

Andy Lester

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3 Comments

TyC Over a year ago

What's the benefit of opening files using the three-arguement form?

Andy Lester Over a year ago

It's clearer, and you don't have to worry about filenames with special characters in them.

TLP Over a year ago

Well... the benefit of the lexical file handle is that it is not global and it autocloses when it goes out of scope. The explicit open mode prevents the dynamic and sometimes dangerous open mode to be used. For example, open FOO, $bar is dangerous if $bar = "< somefile; rm -rf /".

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