Learn Perl and get Minimal Perl for Unix and Linux People to start being productive right away. You'll get the essentials and chapters like:

• Perl as a (better) grep command
• Perl as a (better) sed command
• Perl as a (better) awk command

You'll probably get more than enough Perl to achieve most of your goals but if you want to go deeper, this language and the huge library of resources will allow for that. As mentioned, if you want to try Javascript or Ruby later on, the transition will be fairly easy.

Good luck.