It depends on what you're doing also. Once when I rewrote a third-party utility in perl, rewriting this bit caused it to go slower in perl:

grep "^function" *.4gl |
sed "s/\(.*\):function \(.*\)(.*/\2   \1      \/^function \2(/"
[download]

But the above was wrong, so I rewrote a "correct" perl version :

/^\s*function\s+(\w+)\s*\(/i
#  and then use hashes to save data so there's no s///
[download]

I rewrote the new perl version in shell (grep/sed) for kicks, and it was slower than the perl version (and much uglier).