UNIX for Dummies Questions & Answers

Mac people run screaming into the night when you show them byte streams and shells!

The Bourne shell (sh), named for it's creator at AT&T Bell Labs Stephen R. Bourne - Wikipedia, the free encyclopedia, was the precursor to the ksh (Korn shell, named for it's creator at AT&T Bell Labs http://en.wikipedia.org/wiki/David_K...uter_scientist) ) and bash (born again shell, written by Fox for GNU http://en.wikipedia.org/wiki/Bash_(Unix_shell)), and being simpler might be infinitesimally faster. However, the ksh and bash provide a much richer Character User Interface, for more capabilities and allowing simpler, shorter, more intuitive scripts and command sequences. The csh, written by Bill Joy at U C Berkeley C shell - Wikipedia, the free encyclopedia, is a sort of side offshoot, much less sh compatible, highly flavored to the C language, and a bit more advanced than the Bourne shell, but most find the ksh or bash more desirable. The bash does a bit more than even the latest ksh93, and is fairly compatible. The ksh and other shells have flavored offshoots, like dtksh and tcsh, with extended capabilities for certain contexts. Some command line and ksh features depend on open fd's being mapped into the file system, usually like for instance on Solaris, /dev/fd/0 and /dev/stdin.

It's actually two syntaxes. $() is the modern version of backticks, added because backticks are awkward for nesting:

Code:

# nesting backticks
echo `echo \`echo asdf\``
# nesting $()
echo $(echo $(echo asdf) )

The double quotes just do what double quotes always do, preventing a string from being split apart. I quote everything habitually, but if you know for sure the output will never contain any whitespace, you can leave the double quotes off.