I have a Perl script in which I perform web service calls in a loop. The server returns a multivalued HTTP header that I need to parse after each call with information that I will need to make the next call (if it doesn't return the header, I want to exit the loop).
I only care about one of the values in the header, and I need to get the information out of it with a regular expression. Let's say the header is like this, and I only care about the "foo" value:
X-Header: test-abc12345; blah=foo
X-Header: test-fgasjhgakg; blah=bar
I can get the header values like this: @values = $response->header( 'X-Header' );
. But how do I quickly check if
Ideally, I'd like to do something like this:
my $value = 'default';
do {
# (do HTTP request; use $value)
@values = $response->header( 'X-Header' );
} while( $value = first { /(?:test-)([^;]+)(?:; blah=foo)/ } @values );
But grep
, first
(from List::Util
), etc. all return the entire match and not just the single capturing group I want. I want to avoid cluttering up my code by looping over the array and matching/parsing inside the loop body.
Is what I want possible? What would be the most compact way to write it? So far, all I can come up with is using lookarounds and \K
to discard the stuff I don't care about, but this isn't super readable and makes the regex engine perform a lot of unnecessary steps.
So it seems that you want to catch the first element with a certain pattern, but acquire only the pattern. And you want it done nicely. Indeed, first
and grep
only pass the element itself.
However, List::MoreUtils::first_result does support processing of its match
use List::MoreUtils 0.406 qw(first_result);
my @w = qw(a bit c dIT); # get first "it" case-insensitive
my $res = first_result { ( /(it)/i )[0] } @w;
say $res // 'undef'; #--> it
That ( ... )[0]
is needed to put the regex in the list context so that it returns the actual capture. Another way would be firstres { my ($r) = /(it)/i; $r }
. Pick your choice
For the data in the question
use warnings;
use strict;
use feature 'say';
use List::MoreUtils 0.406 qw(firstres);
my @data = (
'X-Header: test-abc12345; blah=foo',
'X-Header: test-fgasjhgakg; blah=bar'
);
if (my $r = firstres { ( /test-([^;]+);\s+blah=foo/ )[0] } @data) {
say $r
}
Prints abc12345
, clarified in a comment to be the sought result.
Module versions prior to 0.406
(of 2015-03-03) didn't have firstres
(alias first_result
)