Perl regular expression built from values in variables

Question

Given the variables:

my $var1 = "fish";
my $var2 = "ocean";

My input strings can be either fishin_ocean or fishout_ocean.

How do I write a Perl regex to match both the input strings, where parts of the regex are in $var1 and $var2? This one (where the string is in $var3) doesn't return either of the above strings:

  $var3 =~ /$var1.+?$var2/;

Edit from OP's answer:

I think it is the special square braket at the end that is causing the problem

    my $a = "slash_wideiscan"; my $b = "_mnn3h_reg[0]";
    my @array1 = qw (slash_wideiscanps_mnn3h_reg[0] 
                     slash_wideiscanptlr_mnn3h_reg[0] 
                     slash_wideiscanps_mnn0h_reg);
    for my $element (@array1) {
        if ($element =~ /($a.+?$b)/) {
            print "YES : $element\n";
        } else {
            print "NO : $element\n";
        }
    }

Answer that came back was

    NO : slash_wideiscanps_mnn3h_reg[0]
    NO : slash_wideiscanptlr_mnn3h_reg[0]
    NO : slash_wideiscanps_mnn0h_reg

I actually want

    YES : slash_wideiscanps_mnn3h_reg[0]
    YES : slash_wideiscanptlr_mnn3h_reg[0]
    NO : slash_wideiscanps_mnn0h_reg

What exactly are you trying to achieve? The matching operator does not return a string in scalar context. — choroba
– choroba, Commented Jun 13, 2012 at 0:50
Welcome to StackOverflow. Please note that we value clear questions. Please see the FAQ. I've edited the question for you, but I may have misinterpreted what you are after. If so, you should re-edit the question so it reflects what you are really asking. — Jonathan Leffler
– Jonathan Leffler, Commented Jun 13, 2012 at 0:55
You should use proper names for your variables. It will make your life easier. — TLP
– TLP, Commented Jun 13, 2012 at 0:59

TLP · Accepted Answer · 2012-06-13 00:54:01Z

1

Not quite clear what you are looking for, but here is your regex in action:

my $fish  = "fish";
my $ocean = "ocean";

for my $word ("fishin_ocean", "fishout_ocean") {
    if ($word =~ /($fish.+?$ocean)/) {  # parens capture to $1
         print "Word $word matches\n";
         print "The matching part is: $1\n";  # $1 contains the captured text
    }
}

More info in perldoc perlretut and perldoc perlre

answered Jun 13, 2012 at 0:54

TLP

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Comments

gpojd · Accepted Answer · 2012-06-13 00:48:06Z

0

This should work:

/fish(in|out)_ocean/

answered Jun 13, 2012 at 0:48

gpojd

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2 Comments

cosmo kramer Over a year ago

Unfortunately there can be a ton of stuff after fish not just "in" or "out".that's why I was trying out a wildcard character

gpojd Over a year ago

I was thrown off by, "My input strings can be either fishin_ocean or fishout_ocean."

Dondi Michael Stroma · Accepted Answer · 2012-06-13 06:50:57Z

0

You regex is fine. The problem is that you are thinking the regex returns the matched string, but in reality, it only returns true or false (if it matches or does not match).

If you want to capture a match, use parentheses around the part you want to capture. Captures are stored in order in $1, $2, $3, etc...

my ($var1, $var2, $var3) = ("fish", "ocean", "fishin_ocean")

$var3 =~ /($var1)(.+?$var2)/;    # only returns true or false
print $1;                        # prints fish
print $2;                        # prints in_ocean

answered Jun 13, 2012 at 6:50

Dondi Michael Stroma

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Comments

Toto · Accepted Answer · 2012-06-13 15:18:34Z

0

According to your answer (that must be an update to your question), escape each part of your regex with \Q\E like the following:

my $a = "slash_wideiscan"; 
my $b = "_mnn3h_reg[0]";
my @array1 = qw (slash_wideiscanps_mnn3h_reg[0] 
                 slash_wideiscanptlr_mnn3h_reg[0] 
                 slash_wideiscanps_mnn0h_reg);
for my $element (@array1) {
    if ($element =~ /(\Q$a\E.+?\Q$b\E)/) {
               here___^   ^    ^   ^
        print "YES : $element\n";
    } else {
        print "NO : $element\n";
    }
}

output:

YES : slash_wideiscanps_mnn3h_reg[0]
YES : slash_wideiscanptlr_mnn3h_reg[0]
NO : slash_wideiscanps_mnn0h_reg

answered Jun 13, 2012 at 15:18

Toto

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