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"Perl" and "perl" but not "PERL"

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One can often see the Perl programming language referred to as "perl", "Perl" or even "PERL". This page aims to explain what is the difference between all of them, to the uninitiated.

  1. "Perl" is the name of the programming language itself. It had several versions — starting from version 1 up to version 5 which is the current popular version, as well as Perl 6 which is currently under development and won't be compatible with Perl 5 and below. So if you want to refer to the language say "Perl" with a capital "P" and the other letters as lowercase.

  2. "perl" (with all-lowercase) is the name of the command line executable that compiles and runs Perl programs. The implementation, if you may.

  3. In any case, one should never write "PERL" with all uppercase letters, as Perl is not an acronym. If you encounter such a use, it usually indicates that its author does not know enough about Perl, as writing "Perl" or "perl" instead of "PERL" is a Shibboleth that indicates that the speaker or writer knows what they are saying.

A popular idiom, attributed to Tom Christiansen, says that “Only perl can parse Perl.”. Take some time to think about it.