When to use them: awk - never - S. Lott.
I think S. Lott slightly missed the mark with this recommendation. The fact is, on Linux and the other UNIX environments, awk is a useful tool to be used with bash, sh, and ksh for quick text processings. The idea of scripting itself is you solve your problem by gluing together this tool, that tool. Hence in admin scripts, it is common to has ls, grep, |, awk, time, ps, etc. Each is a tool that the scripter combines like a builder brick by brick to finish the building (to solve the problem at hand).
For instance I am a team member of the team managing paintball gear supplies dotcom. This e-commerce site is based on the LAMP stack. For automated processing and normalizing data feeds from various suppliers into the back end database, we employ and maintain a diversified mix of scripts, including bash, perl, php, and even expect. Each has its strengths based on the available modules and API. In the bash scripts we do quick patterns match and appropriate actions on the patterns as needed using awk without the need to switch to PERL. One thing I would also like to point out, which has not been emphasized in the thread, is that a fair number of these scripts were purchased, or gotten from the open source. If the script came as Perl, we maintain it as Perl; if the script came as Php, we maintain it as Php; if it came as bash, we maintain it as bash; we do not re-write it in another language just because we think it is less efficient in the original language.