brackets used in bash

shanenin · Posted: Tue May 03, 2005 5:37 pm Post subject: brackets used in bash

I copied thsi script out of a shell scripting book(mildly changed)

gentsquash · Posted: Tue May 03, 2005 6:48 pm Post subject:

ASIDE: The symbols { } are braces. Brackets are [ ] ;
parentheses are ( ) . One can use "generalized parentheses" for
all these and several others.

For your question, I am not sure. I *think*, in this instance,
that the braces do not make a difference. In other contexts,
they can. If HOME expanded to several words, some of which could
be interpreted as Bash commands, then they would be interpreted
as such in $HOME.

E.g, if $HOME started a command, and it expanded to "if ..."

I *think*, but am not sure, that -in contrast- the contents
of ${HOME} are not interpreted as part of the Bash command
language.

Lets hope that a cognoscento can comment on this.
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IvanYosifov · l33t Joined: 15 Oct 2004 Posts: 778 Location: Bulgaria

$VAR and ${VAR} do exactly the same thing. The difference is that if VAR ( the name of the var ) contains underscores ( maybe other things ) you can't use the first form.

tomk · Posted: Tue May 03, 2005 7:13 pm Post subject:

They are used to distinguish a variable when it could be ambiguous, take this example:

pjp · Administrator Joined: 16 Apr 2002 Posts: 20609

An example is probably the best. Consider $var the lazy method, where ${var} is the "safe" method.

Assume you have a list of files a_file, b_file, c_file, ...
This wouldn't work:

shanenin · Posted: Tue May 03, 2005 7:25 pm Post subject:

thanks for the explanations
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armstrtw · n00b Joined: 09 Oct 2003 Posts: 18

Can someone help me with a similar bash script question?

I have a list of old filenames and a list of new filenames. I'd like to loop through the list renameing filename[i] to newname[i]. I haven't been able to track down an example of using arrays like this in bash.

Thanks,
Whit

Here's a sketch of the program:

oldnames = { oldname1 oldname2 oldname3}
newnames = {newname1 newname2 newname3}

for(i=0; i < length(oldnames); i++) {
mv oldname newname
}

tomk · Posted: Tue May 17, 2005 6:40 pm Post subject:

TrueDFX · Retired Dev Joined: 02 Jun 2004 Posts: 1348

The first part of that can also be written like this in bash:

armstrtw · n00b Joined: 09 Oct 2003 Posts: 18

Perfect!

I also found an example of static initialization here:
http://www.tldp.org/LDP/abs/html/arrays.html

array=( zero one two three four five )
# Element 0 1 2 3 4 5

Thanks for your help. I'm off and running now.

Cheers,
Whit