Reference reading for shell script

I have read three excellent Applescript books: AppleScript 123 (Soghoian), Learn AppleScript (Sanderson) and my favourite, AppleScript (Neuberg). And I am planning to move on to the next stage.

I am currently doing quite a bit of customization on DevonThink 3.0. A significant element of one of my script is for tagging. First, user (me) will set up keywords in two custom metadata fields. The two fields are attached to each tag (a DT object) within groups of tags, one field holds the words for OR matches, and another field for AND matches. My script will search for matches between the keywords in those fields and a text or pdf+text file in the DT (name only or single-word-based concordance of the content). Based on the matches, the script will suggest the appropriate tags be used for the document. Although Applescript can handle direct word-for-word matches well, I am aware that grep or sed can provide much powerful search/matches/replacement by RegEx.

I am looking for advice on reference reading that can help me to integrate the knowledge of grep/sed, RegEx, and how to use shell script effectively within Applescript. There are numerous valuable tips on the web for specific problems, but I prefer books for a broader and more fundamental perspective.

Any guidance from this forum is very much appreciated!

AppleScript can also provide regular expressions via AppleScriptObjC. And you can access it very simply using my RegexAndStuffLib script library, available here:

Unless you have a particular reason for wanting to use shell scripting, the above, or code similar to it, is arguably a better approach.

Thank you very much again.
I will go through the info and study it.