Perl

Perl was created in 1987 by Larry Wall, a linguist working as a programmer, to pull reports out of text files more easily than shell scripts and awk allowed. Its regular expressions became the model most other languages copied, and in the 1990s it ran much of the early web, along with a great deal of system administration and, for a while, the Human Genome Project’s data processing. Its motto is “There’s more than one way to do it.”

Every variable name starts with a sigil that says what it holds: $ a single value, @ an array, and % a hash, Perl’s dictionary. The same array can be read in different contexts, so @values gives the list, while my $n = @values gives its length. Perl ships with a set of core modules, such as List::Util for sum, min, and max. Modules from CPAN, Perl’s package archive, aren’t installed here. Every program starts with use strict and use warnings, and the run script fails the run if Perl prints any warning.

Quirks

• A plain sort compares text, so sort (10, 9) gives 10, 9. Numbers need sort { $a <=> $b }.
• Numbers and strings have separate operators: == and < compare numbers, while eq and lt compare text. "10" == 10.0 is true, but "10" eq "10.0" is false.
• The strings "0" and "" are false, but "0.0", "00", and " " are true.
• / always divides exactly, so -7 / 2 is −3.5. int drops the fraction, giving −3, while % takes the sign of the right side: -7 % 3 is 2.
• "3 apples" + 2 is 5, with only a warning.
• split /,/ drops empty fields at the end, so "1,2,,4,," splits into four fields. A limit of −1 keeps all six.
• Hash order changes from run to run: the same seven keys came out as cbegadf one time and bcegafd the next.
• Reading past the end of an array or a missing hash key gives undef, not an error.
• An integer too big for 64 bits quietly becomes a float: 18446744073709551615 + 1 prints 1.84467440737096e+19.

git clone https://github.com/qnixon/dswithx.git
cd dswithx
python3 harness/run_tests.py --language perl