[H-GEN] Useful bash Variable Manipulations

[Anthony Towns]

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Hello world,

Ever tried typing "mv *.asc *.txt" to rename all your .asc files to
.txt?

And have you noticed how it doesn't work? (Newbies -- this is your cue
to try it. Don't do it where there are important files though)

Even though it _does_ work under _DOS_?

Well, have I got a tip for _you_!


	``  for i in *.txt; do mv $i ${i%.asc}.txt; done  ''


(okay, so it's harder than "C:\> move *.asc *.txt". The Unix way of
expanding wild card before the program is called is better enough in
general to make up for it) 


Basically, if you want to trim stuff off the end of a variable, use

	${variable%pattern-to-trim}

and if you want to trim stuff off the beginning, use

	${variable#pattern-to-trim}

Replacing # with ## and % with %%, will change it's behaviour from
trimming the shortest possible string to trimming the longest possible
string.

Note that the right hand side is _not_ a regexp, but rather uses the
same syntax as filename wildcards.

You can also do search and replace, determine the length of your
variable, obtain substrings and fill in default values.

Very nifty.

Search for "Parameter Expansion" in the bash manpage.

Cheers,
aj

- --
Anthony Towns <aj at humbug.org.au> <http://student.uq.edu.au/~s343676/>
I don't speak for anyone save myself. PGP encrypted mail preferred.

``Like the ski resort of girls looking for husbands and husbands looking
  for girls, the situation is not as symmetrical as it might seem.''

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