Perl incorporated regular expressions into a general purpose programming language in a way that seemed fairly unique at the time. Today they seem to be everywhere, often with the help of PCRE-Perl compatible regexps.
The problem with perl and this kind of list is that in reality it's just an elegant way of writing awk/sh scripts with proper flow control, i.e. like python today it was seen as an way to get around the compatibility and performance issues associated with shell/awk in the bad old days of commercial Unix.
It might sound strange to modern eyes but there was an time when Perl was considered elegant and robust, but then again very few young people have ever experienced the horrors of trying to write portable shell code for commercial Unix, perl was on the other hand almost completely identical regardless of what variant of Unix you happened to be running, and vastly faster then sh/awk at a time when even expensive systems could be slow by modern standards.
For modern day script writers Ruby and Python have all but replaced perl even though that's not stopping the enterprise from keeping their perl codebases alive and kicking for the foreseeable future, but even there it's being challenged from bellow by the fact that bash and gawk have become fairly universal on Linux systems and hardware fast enough that regex performance rarely matter.
In my mind what Perl brought to awk/sh was not flow control but rather data structures that did not make you want to kill yourself. Its standard library also delivered a lot of core sysadmin functionality back in the day and the reporting/output features fit very well with what was needed for early web CGI scripting.
It might sound strange to modern eyes but there was an time when Perl was considered elegant and robust, but then again very few young people have ever experienced the horrors of trying to write portable shell code for commercial Unix, perl was on the other hand almost completely identical regardless of what variant of Unix you happened to be running, and vastly faster then sh/awk at a time when even expensive systems could be slow by modern standards.
For modern day script writers Ruby and Python have all but replaced perl even though that's not stopping the enterprise from keeping their perl codebases alive and kicking for the foreseeable future, but even there it's being challenged from bellow by the fact that bash and gawk have become fairly universal on Linux systems and hardware fast enough that regex performance rarely matter.