topic Shell script: Brace expansion in Operating System - Linux

Shell script: Brace expansion

SGK — Wed, 12 Jul 2006 02:21:51 GMT

Hi,

The following two brace expansion working differently. Can someone explain how this works?

# echo {file1,file2}\ :{\ A," B",' C'}
file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C

# echo {file1,file2} :{\ A," B",' C'}
file1 file2 : A : B : C

TIA.

Re: Shell script: Brace expansion

Ivan Ferreira — Wed, 12 Jul 2006 08:43:43 GMT

I just tested both expressions and I have the same result. That is, both returns the same output:

file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C

Re: Shell script: Brace expansion

SGK — Wed, 12 Jul 2006 22:16:45 GMT

Under which shell you tried?

# echo $SHELL
/bin/bash

# echo {file1,file2} :{\ A," B",' C'}
file1 file2 : A : B : C

Re: Shell script: Brace expansion

Jeroen Peereboom — Thu, 13 Jul 2006 00:38:35 GMT

>echo $SHELL
/bin/bash
> echo {file1,file2}\ :{\ A," B",' C'}
file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C
>echo {file1,file2}\ :{\ A," B",' C'}
file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C

No differences?

JP

Re: Shell script: Brace expansion

Alexander Chuzhoy — Thu, 13 Jul 2006 01:01:07 GMT

I get the same behavior as you did.
Use BASH shell on rhel4.2

Re: Shell script: Brace expansion

Jeroen Peereboom — Thu, 13 Jul 2006 01:05:20 GMT

Oops...

>echo {file1,file2}\ :{\ A," B",' C'}
file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C
>echo {file1,file2} :{\ A," B",' C'}
file1 file2 : A : B : C

Difference in commands: the back-slash to escape the space before the colon.
Man page:
A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma. Any incorrectly formed brace expansion is left unchanged.
I don't think that helps.

If you escape the space with a backslash, the space is part of the string. If you do not escape the space, it is a separator and there is nothing to expand in the two separate brace lists...

JP

Re: Shell script: Brace expansion

Jeroen Peereboom — Thu, 13 Jul 2006 05:54:18 GMT

And also:

echo {file1,file2}" : "{\ A," B",' C'}
file1 : A file1 : B file1 : C file2 : A file2 : B file2 : C

JP

Re: Shell script: Brace expansion

Ryan Goh — Wed, 19 Jul 2006 23:39:39 GMT

Try this

# echo {file1,file2}:{\ A," B",' C'}

You should get the result below:

file1: A file1: B file1: C file2: A file2: B file2: C

Because of additional space in between of } and : , that why get the problem look like below:

file1 file2 : A : B : C

Re: Shell script: Brace expansion

SGK — Thu, 20 Jul 2006 00:00:19 GMT

Thanks all to clarify my doubts