Perl: Sort Hash Values by Key with a Hash Slice

In Perl, hash (associative array) sorting is a common and easy practice. Sorting values by key is easy. And so is sorting by value. But how do you sort the values of a hash by key? One answer is to use a hash slice. Continue reading

Perl – OR Pattern Match Slow, Use Two Patterns Instead

A handy feature of regular expressions is their ability to “or” match. Searching for two strings in a file is easy with a construct like “egrep ‘root|uucp’ /etc/passwd”. The vertical bar (“|”) acts as an “or” operator. Perl supports the vertical bar too, and the same match could be achieved in Perl thus:

bash-4.2$ perl -n -e 'print $_ if /root|uucp/' < /etc/passwd root:x:0:0:root:/root:/bin/bash uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin

Weirdly though, this construction is up to 10 times slower than 2 separate matches performing the same search, as can be shown with a quick demonstration. Continue reading