Capture word between optional hyphens regex - regex

Question

I've following type of strings,
abc - xyz
abc - pqr - xyz
abc - - xyz
abc - pqr uvw - xyz
I want to retrieve the text xyz from 1st string and pqr from 2nd string, `` (empty) from 3rd & pqr uvw. The 2nd hyphen is optional. abc is static string, it has to be there. I've tried following regex,
/^(?:abc) - (.*)[^ -]?/
But it gives me following output,
xyz
pqr - xyz
- xyz
pqr uvw - xyz
I don't need the last part in the second string. I'm using perl for scripting. Can it be done via regex?

Answer 1

Note that (.*) part is a greedily quantified dot and it grabs any 0+ chars other than line break chars, as many as possible, up to the end of the line and the [^ -]?, being able to match an empty string due to the ? quantifier (1 or 0 repetitions), matches the empty string at the end of the line. Thus, pqr - xyz output for abc - pqr - xyz is only logical for the regex engine.
You need to use a more restrictive pattern here. E.g.
/^abc\h*-\h*((?:[^\s-]+(?:\h+[^\s-]+)*)?)/
See the regex demo.
Details
^ - start of a string
abc - an abc
\h*-\h* - a hyphen enclosed with 0+ horizontal whitespaces
((?:[^\s-]+(?:\h+[^\s-]+)*)?) - Group 1 capturing an optional occurrence of
[^\s-]+ - 1 or more chars other than whitespace and -
(?:\h+[^\s-]+)* - zero or more repetitions of
\h+ - 1+ horizontal whitespaces
[^\s-]+ - 1 or more chars other than whitespace and -

Answer 2

You could use ^[^-]*-\s*\K[^\s-]*.
Here's how it works:
^ # Matches at the beginning of the line (in multiline mode)
[^-]* # Matches every non - characters
- # Followed by -
\s* # Matches every spacing characters
\K # Reset match at current position
[^\s-]* # Matches every non-spacing or - characters
Demo.
Update for multiple enclosed words: ^[^-]*-\s*\K[^\s-]*(?:\s*[^\s-]+)*
Last part (?:\s*[^\s-]+)* checks for existence of any other word preceded by space(s).
Demo

Answer 3

You could use split:
$answer = (split / \- /, $t)[1];
Where $t is the text string and you want the 2nd split (i.e. [1] as starts from 0). Works for everything except abc - - xyz but if the separator is " - " then it should have 2 spaces in the middle to return nothing. If abc - - xyz is correct then you can do this before the split for all to work:
$t =~ s/\- \-/- -/;
It simply inserts an extra space so it'll match " - " twice with nothing in-between.

Answer 4

Can it be done via regex?
Yes, with three simple regexes: - and ^\s+ and \s+$.
use strict;
use warnings;
use 5.020;
use autodie;
use Data::Dumper;
open my $INFILE, '<', 'data.txt';
my #results = map {
(undef, my $target) = split /-/, $_, 3;
$target =~ s/^\s+//; #remove leading spaces
$target =~ s/\s+$//; #remove trailing spaces
$target;
} <$INFILE>;
close $INFILE;
say Dumper \#results;
--output:--
$VAR1 = [
'xyz',
'pqr',
'',
'pqr uvw'
];