In the old days, shells were capable of little more than calling external programs and executing basic, internal commands. With all the bells and whistles in the latest versions of Bash, however, you hardly need the support of external tools.
Many scripts treat Bash as if it were capable of little more than calling external programs. This is surprising, since version 2 of the default shell has a command set that covers everything from complex string manipulation, through regular expressions, to arrays; useful functions that make expensive program calls redundant. The main advantage of internal functions is that the shell does not need to spawn a new process, which saves processing time and memory. This capability can be important, particularly if you need to launch a program like grep or cut in a loop, as the completion time and memory consumption of a script can explode if you’re not careful. This article describes some simple techiques for speeding up your Bash scripts.
Look here for archived tutorials and talks from USENIX Security '08. Each comprises a video and recorded presentation slides which are shown parallel to the talk.
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