These are meant to be run from the command line on Unix-like systems. So far all of these are Perl scripts (work on 5.8.8 and/or 5.16.2 on Mac OS X, at least), so you can run them like any other Perl program (though they all need arguments); they should also work if set to executable. Many of these are fairly simple, so you could probably find similar things elsewhere. All are less than 3 kilobytes except plgrep.
Contents: base64, http-head, plgrep, perl-repl, thirdperson, uuniq
Encode or decode base 64 text.
Usage: base64 -e|-d [file...]. -e for encode, -d for decode. The option must be specified, and no other options are supported.
Show the HTTP headers for any given URL.
Usage: http-head url [headers ...]. (No options.)
Updated 2014-08-28: allows specifying additional HTTP headers, one header per argument. E.g., http-head www.example.com 'User-Agent: Mozilla/5.0'
Updated 2014-11-04: fixes a bug that caused it not to work with certain servers
Like grep, but uses Perl syntax, since the version of grep that came with my computer doesn't use Perl syntax.
Updated 2016-12-15 (version 3.0.1).
Some differences from normal grep (besides using Perl regular expressions and not supporting all options):
--color highlights the filename and line number as well as the match to make it easier to tell lines apart in multi-line matches. It can also be abbreviated -c.
-r, and if recursion is enabled the default file is the current directory rather than standard input.
--include and exclude can be abbreviated -I and -E
-A
-e), all of which must match.
More information (includes help and older versions); Download plgrep (10.85K) (source)
Prompts for Perl commands, then executes them. Other interpreters have this feature built-in, but I couldn't find it for Perl, so I made one. (Stands for Read–eval–print loop.)
Known issues: Currently there's no built-in functionality to start by loading subroutines from a file. The use command still seems to work, though. Also no line editing. Also if the command you type is a print statement, it prints the return value of print (usually 1, indicating success) afterwards.
Updated 2014-06-02: Control-C stops the currently-running command.
Not really useful, but may be mildly interesting. Converts first-person text into third-person text.
Like uniq, but matches lines that are not next to each other.
Usage: uuniq [-cdilu] [-f #] [-c #] [file...]