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

Hello Monks,

I always find myself wanting to use an equivalent to grep on windows and seek a perl solution. I tracked down a script on the net and gave it some polishing up. It seems to behave.

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

use File::Find;

=pod
 
=head1 DESCRIPTION
 
Usage: perl grep1.pl frobnitz txt
 
=cut

my $search_pattern=$ARGV[0];
my $file_pattern  =$ARGV[1];

find(\&d, cwd);

sub d {

  my $file = $File::Find::name;

  $file =~ s,/,\\,g;

  return unless -f $file;
  return unless $file =~ /$file_pattern/;

  open my $fh, $file or print "couldn't open $file\n" && return;

  while (<$fh>) {
    if (my ($found) = m/($search_pattern)/o) {
      print "found $found in $file\n";
      last;
    }
  }

  close $fh;
}

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My question is what this line is doing:

$file =~ s,/,\\,g;

Also accepting any criticisms/improvements.

Replies are listed 'Best First'.
Re: grep for windows
by RonW (Parson) on Oct 15, 2016 at 02:41 UTC
    My question is what this line is doing:
    $file =~ s,/,\\,g;

    It is replacing / characters with \ characters in $file. The g causes the replacement to apply to all occurrences.

    Commas were used as the delimiters to avoid escaping the / character. An equivalent statement would be:

    $file =~ s/\//\\/g;

    Which many people find harder to read.

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Re: grep for windows
by Athanasius (Cardinal) on Oct 15, 2016 at 03:05 UTC

    Hello Datz_cozee75,

    Fleshing out RonW’s answer a little:

    My question is what this line is doing:

    $file =~ s,/,\\,g;

    It’s replacing / (forward slash) with \\ (backslash) throughout the string $file.

    Here, s introduces the substitution operator. It’s normally written s///, but since the string to be substituted is itself a forward slash, a different delimiter has been chosen: a , (comma). See perlretut#Simple-word-matching.

    The backslash is doubled because a single backslash introduces an escape sequence — see perlop#Quote-and-Quote-like-Operators. So two consecutive backslashes represent an actual (single!) backslash character.

    And of course the /g modifier on the regex causes the substitution to be made globally throughout the string. See perlre#Modifiers.

    Hope that helps,

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: grep for windows
by BrowserUk (Patriarch) on Oct 15, 2016 at 00:53 UTC

    Have you ever typed: findstr /? at a windows command line prompt? If not, try it.

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
    In the absence of evidence, opinion is indistinguishable from prejudice.
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[d/l]

      Thx all for responses...they covered the gamut pretty well. I was unaware of this native use of msdos, and there is something to be said for going at a problem in its native environment. The recursive form was what I was looking for:

      C:\Users\Fred\Desktop>findstr /s Neskowin *.txt
handyman\template_stuff\captions\a.txt:I'm dragging my tools out again
+, getting them sharpened, adjusted for altitude. I can't help but not
+ice that your Neskowin property needs a lot of the type of TLC I arri
+ve with, beginning with oil for hinges.

      [download]

      Examples here: https://www.windows-commandline.com/findstr-command-examples-regular/

      Cheers,

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Re: grep for windows
by VinsWorldcom (Prior) on Oct 15, 2016 at 00:55 UTC
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      on the same side you can also try unxutils

      L*

      There are no rules, there are no thumbs..
      Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
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Re: grep for windows
by clueless newbie (Curate) on Oct 15, 2016 at 00:53 UTC
    Since you were looking for something equivalent to grep, perhaps you'd be interested in ack.
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      Few weeks ago I could not install ack 2, for the same purpose as OP, due to problem with Find::Next. Other details are there.

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        Few weeks ago I could not install ack 2, for the same purpose as OP, due to problem with Find::Next. Other details are there.

        When a test fails because it couldn't create a temp file in a non existent temp directory ... force install it

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Re: grep for windows
by NetWallah (Canon) on Oct 15, 2016 at 18:08 UTC
    Just adding a point of interest - RonW and Athanasius explain how to avoid the Leaning toothpick syndrome, which is also mentioned in perlop:

    ... you can use any pair of non-whitespace (ASCII) characters as delimiters. This is particularly useful for matching path names that contain "/" , to avoid LTS (leaning toothpick syndrome).

            ...it is unhealthy to remain near things that are in the process of blowing up.     man page for WARP, by Larry Wall

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Re: grep for windows (perlpowertools)
by Anonymous Monk on Oct 15, 2016 at 01:48 UTC
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