Comments on: Bash parameter expansion cheatsheet http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/ Stay curious! Thu, 09 Feb 2012 09:56:43 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: find command in unix http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/#comment-19457 find command in unix Mon, 27 Jun 2011 08:13:20 +0000 http://www.xaprb.com/blog/?p=316#comment-19457 Important point to note is that <a href="http://javarevisited.blogspot.com/2011/06/special-bash-parameters-in-script-linux.html" rel="nofollow"> $* and $@ bash parameters </a> behave identical without double quotes but entirely different if used within double quotes. in case of $* individual parameters will be separated by IFS characters while in case of $@ individual parameters will appear in quotes and separated by space. Important point to note is that $* and $@ bash parameters behave identical without double quotes but entirely different if used within double quotes. in case of $* individual parameters will be separated by IFS characters while in case of $@ individual parameters will appear in quotes and separated by space.

]]> By: Keith T http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/#comment-19174 Keith T Wed, 23 Feb 2011 18:45:18 +0000 http://www.xaprb.com/blog/?p=316#comment-19174 Using eval and echo you can kludge up nested parameter expansion. Let's say you have $param1 and $param2. param1="Hi" and param2="There". You have a routine you want to reuse, wherein all you have to pass it is 1 or 2 and it will use the appropriate $param1 or $param2. You set INDEX=1 or INDEX=2 depending on which one you want. > INDEX=1 > echo $(eval echo $(eval 'echo \$\{param$INDEX\}')) Hi > INDEX=2 > echo $(eval echo $(eval 'echo \$\{param$INDEX\}')) There It's convoluted for sure, but it works. Using eval and echo you can kludge up nested parameter expansion.

Let’s say you have $param1 and $param2. param1=”Hi” and param2=”There”. You have a routine you want to reuse, wherein all you have to pass it is 1 or 2 and it will use the appropriate $param1 or $param2.

You set INDEX=1 or INDEX=2 depending on which one you want.

> INDEX=1
> echo $(eval echo $(eval ‘echo \$\{param$INDEX\}’))
Hi
> INDEX=2
> echo $(eval echo $(eval ‘echo \$\{param$INDEX\}’))
There

It’s convoluted for sure, but it works.

]]> By: alex5161 http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/#comment-18991 alex5161 Tue, 21 Dec 2010 00:37:24 +0000 http://www.xaprb.com/blog/?p=316#comment-18991 You have one not completely correct example in the pattern matching: " # Oops, I didn't mean that... get rid of the numbers. for file in *.gif; do mv $file ${file##[0-9]}; done " - the ${file##[0-9]} by using '##' should means to remove long matching of number - here that is unappliable: if $file is 'a555name' - nothing matched, as before number there is something else. if $file is '123name' - only first number is matched, while, I guess, assumed to remove '123': it is not happend, because [0-9] - is one number only. To remove '123' it could be ${file#*[0-9]} - no needs for '##', as it would remove up to any found number in the file name, if the name has it. But it is not good enouth, as it, also, would remove 'a555' from the 'a555name', that is not planned. It should be specified as 'any number of diggits from beggining of the variable value', something like : /^[0-9]+/; but pattern expansion is not accepting such syntax. You have one not completely correct example in the pattern matching:
“
# Oops, I didn’t mean that… get rid of the numbers.
for file in *.gif; do mv $file ${file##[0-9]}; done
“
– the ${file##[0-9]} by using ‘##’ should means to remove long matching of number – here that is unappliable:
if $file is ‘a555name’ – nothing matched, as before number there is something else.
if $file is ’123name’ – only first number is matched, while, I guess, assumed to remove ’123′: it is not happend, because [0-9] – is one number only.
To remove ’123′ it could be ${file#*[0-9]} – no needs for ‘##’, as it would remove up to any found number in the file name, if the name has it.
But it is not good enouth, as it, also, would remove ‘a555′ from the ‘a555name’, that is not planned.
It should be specified as ‘any number of diggits from beggining of the variable value’, something like : /^[0-9]+/; but pattern expansion is not accepting such syntax.

]]> By: [bash] Parameter expansions « *NIX tricks http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/#comment-17084 [bash] Parameter expansions « *NIX tricks Thu, 08 Oct 2009 21:13:21 +0000 http://www.xaprb.com/blog/?p=316#comment-17084 [...] Reference: Directly copied from here. [...] [...] Reference: Directly copied from here. [...]

]]> By: Xaprb http://www.xaprb.com/blog/2007/03/29/bash-parameter-expansion-cheatsheet/#comment-5433 Xaprb Sun, 01 Apr 2007 13:11:20 +0000 http://www.xaprb.com/blog/?p=316#comment-5433 <p>Thanks for the tip! I'm currently on an Ubuntu machine and /dev/tcp isn't enabled so I can't test it out, but that is neat!</p> Thanks for the tip! I’m currently on an Ubuntu machine and /dev/tcp isn’t enabled so I can’t test it out, but that is neat!

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