1. Your main call should be:

   grep_file($_) for @ARGV; 
   #            ===
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This will call the grep for each file name.

2. Your "open file" should really be "Process_record" -- to process each record of each file.
The file is already open and read, before that is called.

3. I don't see any code to search through the file(s).

I think you mean:

grep_file($_) for @ARGV;
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toby döt ink

Hi @NetWallah,

Thank you so much for your patience in responding to my question.

I have not tried to perform the pattern search; I thought of trying it later as I wasn't able to get the basics correct.

Actually in the program above, I was thinking of the following:

1. Read in file_list.txt which contains a list of files: a.txt, b.txt, c.txt.

2. Open file_list.txt, and then open the individual files listed in file_list.txt.

Thank you very much for your kind help! :)

#!/usr/bin/perl

use strict;
use warnings;

my ($pattern, @files) = @ARGV;
print "pattern=$pattern  files are:@files\n";

__END__
example:
>mygrep.pl "some pattern" filea fileb filec
pattern=some pattern  files are:filea fileb filec
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Hi Marshall,

Thank you for your help on this! :)

I have tried to do what you have told me, i.e.

Write a program that opens FileA.txt and then prints all lines that contain "asdf". Create FileA.txt with test cases as you wish.

My program is seen below:

#!/usr/bin/perl

use strict;
use warnings;

sub open_file {
    my $file = shift;
    my $pattern = "asdf";
    open FILE, $file;
    while (my $line = <FILE>) {
        if ($line =~ m/$pattern/){
            print $line;
        }
    }
}

open_file@ARGV
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Hence in the command line (Terminal), I did a: ./open_file.pl FileA.txt, and the printouts were correct.

Hi NetWallah, Marshall and members of the PerlMonk community,

Thank you all for your kind help and support. I have managed to solve the question, thanks to an inspiration by Marshall.

My code is shown below:

#!/usr/bin/perl

use strict;
use warnings;

sub grep_file {
    
    my @files = @_;
    my $pattern = "asdf";
    foreach my $file (@files) {
        open FILE, $file;
        while (my $line = <FILE>) {
            if ($line =~ /$pattern/) {
                print $line;
            }
        }
    }

}

grep_file @ARGV
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Thank you all once again! (:

Hello Anonymous Monk,

Perl is a well known scripting language that people choose to create 'Modules' that can assist you / us to reduce our lines of code to minimum. For example reading and loading all lines of a file in an array while removing the new line characters all in one line :)

One of the modules that I usually prefer to use is IO::All.

Then your task is simplified you just need to set the pattern to match (string or even multiple strings) and grep all elements that match your pattern using grep as you have done already :).

Small sample of code bellow:

#!/usr/bin/perl
use strict;
use warnings;

use IO::All;
use Data::Dumper;

foreach my $file (@ARGV) {
    if ( -e $file ) {  # double check existence
    my @lines = io($file)->chomp->slurp; # Chomp as you slurp
    if (my @matches = grep( /string/, @lines ) ) {
        print "Found in File: '$file':\n";
        print Dumper \@matches;
    }
    }
}

__END__

$ perl test.pl a.txt b.txt c.txt
Found in File: 'a.txt':
$VAR1 = [
          'Line two interested, string'
        ];
Found in File: 'b.txt':
$VAR1 = [
          'Line one interested, string',
          'Line two interested, string'
        ];

__DATA__

$ cat a.txt b.txt c.txt
Line one not interested
Line two interested, string
Line one interested, string
Line two interested, string
Line one not interested
Line two not interested
Line three not interested
[download]

You need to adjust it to your preferences but it should be close to what you want to achieve.

Update: I do not want to include the solution with the subroutine. There are several ways to put all your data together. One possible way I would suggest push. Give it a try and we will help you more if you get problems. After all programming / scripting is all about trying and failing until you get it right :)

Hope this helps, BR.

Hi thanos1983,

Thank you for your detailed reply! (:

I will take a look at your suggested solution. :) One thing I am still a bit puzzled about, is how to open a file that contains the names of the files in the current directory, and then iterate through them to print out lines that matches the pattern I want. I am currently still working on that.

Thank you once again!

Hello again Anonymous Monk,

You are welcome :)

Update: Sorry I got your last question completely wrong :). You can repeat the same procedure as you open the files and instead of @ARGV use @files.

Sample of code:

#!/usr/bin/perl
use strict;
use warnings;

use IO::All;
use Data::Dumper;

my @files = io('fileName.txt')->chomp->slurp;
print Dumper \@files;

__END__
$ perl test.pl
$VAR1 = [
          'a.txt',
          'b.txt',
          'c.txt'
        ];
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Update2: I think I finally understood what you mean. You want to provide a file as a parameter to the script that contains the names of the files that you want to search through for the keyword. If this is the case see bellow:

#!/usr/bin/perl
use strict;
use warnings;

use IO::All;
use Data::Dumper;

sub grepFileFromSubroutine {
    my @files = io(shift)->chomp->slurp;
    my @final;
    foreach my $file (@files) {
    if ( -e $file ) {  # double check existence
        my @lines = io($file)->chomp->slurp; # Chomp as you slurp
        if (my @matches = grep( /string/, @lines ) ) {
        push @final, "Found in File: '$file':", @matches;
        }
    }
    }
    return \@final;
}

print Dumper grepFileFromSubroutine(@ARGV);

__END__

$ perl test.pl fileName.txt
$VAR1 = [
          'Found in File: \'a.txt\':',
          'Line two interested, string',
          'Found in File: \'b.txt\':',
          'Line one interested, string',
          'Line two interested, string'
        ];

__DATA__

$ cat a.txt b.txt c.txt
Line one not interested
Line two interested, string
Line one interested, string
Line two interested, string
Line one not interested
Line two not interested
Line three not interested
[download]

If still is not what you want provide us more information to assist you more :)

Regarding your last question read this past question which contains also examples and a variety of solutions (Find filename that has the pattern in a directory).

I usually prefer to use File::Find::Rule. A previously asked question with a sample of code with this module see (Re: Capturing and then opening multiple files).

Hope this helps, BR.

Seeking for Perl wisdom...on the process of learning...not there...yet!

If you look at this:

while (my $line = <FILE>) {
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You'll find that $line is now "a.txt\n". It keeps the line break at the end of the line. Look at the chomp function to resolve that.

Also the following line isn't even doing anything:

my $file = scalar(@_);
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Hi tobyink,

Ah yes, you are right. It keeps getting stuck at the file a.txt and printing only the contents out from it. :( Now I know why. It's because of the "\n". I will read up what chomp does. Thank you for the hint! :) The book "Learn Perl the Hard Way" really lives up to its name. Haha. Oh dear.

Ah yes, I realized that "my $file = scalar(@_)" isn't doing anything too after debugging it yesterday. Thank you for pointing it out. Just wondering, does that statement convert an array "stream" into a scalar quantity, e.g. a string?

Thank you (:

Just wondering, does that statement convert an array "stream" into a scalar quantity, e.g. a string?

Yes, but not the scalar quantity you might imagine. Running scalar on an array or list argument returns the number of elements in the array or list as this is what happens when an array a list is evaluated in scalar context. Conversely, if you wanted a string which was a concatenation of all the elements in the array then you might use join.

#!/usr/bin/env perl 
use strict;
use warnings;

my @foo = ('dog', 'bites', 'man', 'bites', 'dog');
printf "scalar = '%s'\n", scalar @foo;
printf "join = '%s'\n",   join ' ', @foo;
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Update: removed erroneous mentions of lists as their behaviour in scalar context differs from arrays (returns the last item). Thanks choroba for reminding me of this.

You may read perlop for the null filehandle <> and a poor man‘s grep. Regards, Karl

Hi karlgoethebier,

Thank you for your suggestion!

I will read the perlop (:

Thank you! (:

See also

«The Crux of the Biscuit is the Apostrophe»

perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

Hi karlgoethebier,

Thank you for your suggestion!

I will read the perlop (:

Thank you! (:

#!/usr/bin/perl

# https://perlmonks.org/?node_id=1230880

use strict;
use warnings;

my $pattern = shift;
chomp( @ARGV = <> );
/$pattern/ and print while <>;
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