Task — Find pairs

You are given a string of delimiter pairs and a string to search. Write a script to return two strings, the first with any characters matching the “opening character” set, the second with any matching the “closing character” set.

Examples

Example 1:
Input:
    Delimiter pairs: ""[]()
    Search String: "I like (parens) and the Apple
        ][+" they said.
Output:
    "(["
    ")]"

Example 2:
Input:
    Delimiter pairs: **//<>
    Search String: /* This is a comment (in some 
        languages) */ <could be a tag>
Output:
    /**/<
    /**/>

Analysis

The task description is not entirely clear, though the examples help a bit.

My approach is to make strings of the opening and closing characters and then use:

$openers =~ s|[^\Q$opens\E]||g;
$closers =~ s|[^\Q$closes\E]||g;

to remove those characters from the input string.

I hope that's what was wanted.

Try it 

#!/usr/bin/perl
use strict;
use warnings;
use v5.26;

find_pairs('""[]()', '"I like (parens) and the Apple ][+" they said.');
find_pairs('**//<>', '/* This is a comment (in some languages) */ <could be a tag>');
find_pairs('{}##^!', '{note 1} #danger# ^switch off power first! #by order#');

sub find_pairs {

    my ($delimiter_pairs, $search_string, $openers, $closers, $opens, $closes);

    # copy the search string
    ($delimiter_pairs) = $_[0];
    $openers = $closers = $search_string = $_[1];

    # pick off the delimiters in pairs and make strings of the opening and closing characters
    while ($delimiter_pairs =~ m|(.)(.)|g) {
        $opens .= $1;
        $closes .= $2;
    }

    # remove all but the opening characters from $openers and similarly with $closers
    $openers =~ s|[^\Q$opens\E]||g;
    $closers =~ s|[^\Q$closes\E]||g;

    say qq[\nInput:\n   Delimiter pairs: $delimiter_pairs];
    say qq[   Search string: $search_string];
    say qq[Output:\n   $openers];
    say qq[   $closers];
}

last updated 2026-03-09 — 13 lines of code

Output

Input:
   Delimiter pairs: ""[]()
   Search string: "I like (parens) and the Apple ][+" they said.
Output:
   "(["
   ")]"

Input:
   Delimiter pairs: **//<>
   Search string: /* This is a comment (in some languages) */ 
Output:
   /**/<
   /**/>

Input:
   Delimiter pairs: {}##^!
   Search string: {note 1} #danger# ^switch off power first! #by order#
Output:
   {##^##
   }##!##