capture optional text

Lotus1 has asked for the wisdom of the Perl Monks concerning the following question:

I got this program to work but it seems like there could be a better way to do this. I have a text file with server host names followed by optional comments. Any suggestions?

use warnings;
use strict;
use Data::Dumper;

my %hosts;

#### file format is hostname space optional #'s followed by comment
while(<DATA>) {
    chomp;
    my $host;
    my $comment;
    if(/^\s*(\w+)\s*#+(.*$)/){
        $host = $1;
        $comment = $2;
    }
    elsif(/^\s*(\w+)\s*$/){
        $host = $1;
        $comment = '';
    }
    $hosts{$host} = $comment;
}

print Dumper(\%hosts);

__DATA__
XYZ1ADAIQ1   #AMI
XYZ1ADECQ1   #OAG
XYZ1ADEDQ1  
XYZ1ADEDQ2   ##DMS Host
[download]

The output is:

$VAR1 = {
          'XYZ1ADEDQ1' => '',
          'XYZ1ADECQ1' => 'OAG',
          'XYZ1ADEDQ2' => 'DMS Host',
          'XYZ1ADAIQ1' => 'AMI'
        };
[download]

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Replies are listed 'Best First'.
Re: capture optional text by tybalt89 (Monsignor) on May 17, 2017 at 22:12 UTC
`#!/usr/bin/perl # http://perlmonks.org/?node_id=1190504 use strict; use warnings; use Data::Dumper; my %hosts = map /(\S+)\s+#(.)/, <DATA>; print Dumper \%hosts; __DATA__ XYZ1ADAIQ1 #AMI XYZ1ADECQ1 #OAG XYZ1ADEDQ1 XYZ1ADEDQ2 ##DMS Host` [download]	[reply] [d/l]
Re^2: capture optional text by Lotus1 (Vicar) on May 18, 2017 at 14:40 UTC
I like the idea of the zero or more match, `(.*)`, inside the capture to make it match even if the comment isn't there. Thanks.	[reply] [d/l]
Re^3: capture optional text by KurtZ (Friar) on May 18, 2017 at 16:23 UTC
It will also match "malformed" comments without a leading #.	[reply]
Re^4: capture optional text by tybalt89 (Monsignor) on May 18, 2017 at 16:33 UTC
Re: capture optional text by haukex (Archbishop) on May 18, 2017 at 04:56 UTC
TIMTOWTDI, personally I like to be explicit and use non-capturing groups for this kind of thing, like `(?: ... )?` and/or `(?: ... \| ... )` (although the former gets a little less readable in the example below). The following regex requires there to be a space before the comment, and I've also used the `/x` modifier to make it a bit more readable. `while (<DATA>) { my ($host,$comment) = m{^ \s* (\w+) (?: \s+ \#+ (.) \| \s ) $}x #OR: # m{^ \s* (\w+) (?: \s+ (?: \#+ (.) )? )? $}x or die "failed to parse '$_'"; $hosts{$host} = $comment//''; }` [download] Update:* Yet another option: `m{^ \s* (\w+) \s+ (?: \#+ (.*) )? $}x` - this works because even if there's nothing following the `\w+`, the `\s+` will match the newline, and `$` matches either at the end of the string or at the newline at the end of the string.	[reply] [d/l] [select]
Re: capture optional text by Anonymous Monk on May 17, 2017 at 22:03 UTC
`use strict; use warnings; use Data::Dumper; my %hosts; while (chomp(my $line = <DATA>)) { my ($key,$val) = split /\s+/, $line, 2; $hosts{$key} = $val; } print Dumper \%hosts; __DATA__ XYZ1ADAIQ1 #AMI XYZ1ADECQ1 #OAG XYZ1ADEDQ1 XYZ1ADEDQ2 ##DMS Host` [download]	[reply] [d/l]
Re^2: capture optional text by haukex (Archbishop) on May 18, 2017 at 13:55 UTC
`while (chomp(my $line = <DATA>)) {` This won't work if the final line doesn't end on a newline, as chomp returns the number of newlines it removed. Better to use the traditional `while (<DATA>) { chomp; ...` or `while (my $line = <DATA>) { chomp($line); ...` Update: Plus, even with a trailing newline, the code generates a warning, since after the final line, the loop condition is executed one more time, and `<DATA>` will return `undef` and `chomp(my $line = undef)` causes a warning.	[reply] [d/l] [select]
Re^2: capture optional text by Lotus1 (Vicar) on May 18, 2017 at 13:32 UTC
Split should have been my first choice but I didn't think of it. Very nice, thanks.	[reply]