The use of parentheses in the bash shell

**nispio** · 01-22-2010

I have been learning linux for about a year now, and I thought I knew my way around the bash shell fairly well by now, until I deleted a whole folder worth of files on accident. Here's how it happened: I have a homework folder to which I had downloaded a good deal of files, and also had saved a bunch of my homework there. Over the course of the semester, I had inadvertently downloaded some files twice, and firefox placed a "(2)" at the end of duplicate files. I wanted to delete all of the duplicates, so I tried the following:

Code:

 # rm *(2)*

It did not work as expected, it deleted everything. I now know that i should have used:

Code:

# rm *"(2)"*

or

Code:

# rm *\(2\)*

but it's too late for that. I have since been trying to figure out exactly what the parentheses do. I am baffled because I am getting some pretty unexpected results as I play around with them. for example:

Code:

# echo *(2)
*()
# echo *(2)*
emacs-23.1.tar.bz2 final_report_merged.pdf HW%202(2).doc HW%202.doc HW%203.doc site-lisp verilog-mode.el.gz

Can someone help me understand what is happening? What do the parentheses do? Any links to sites that explain in detail would be appreciated as well.

Thanks in advance!

**drl** · 01-23-2010

Hi.

This has to do with extended globbing, an extension of the usual meta-character set:

Code:

* ? [ ... ]

Please look at the section of man bash that describes shopt and extglob:

Code:

       If the extglob shell option is enabled using the shopt builtin, several
       extended pattern matching operators are recognized ...

-- excerpt from man bash, searching for extglob

a few experiments along with that reference should explain things ... cheers, drl

**regexorcist** · 01-24-2010

That's cool drl, I didn't know that... thanks

Parentheses are primarily used to define functions

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