Filename brace expansion in scripts

[Colin Law]

On 18 November 2010 16:01, Loïc Grenié <loic.grenie at gmail.com> wrote:
> 2010/11/18 Colin Law <clanlaw at googlemail.com>:
>> I have a problem with filename expansion in a script and am having
>> difficulty understanding what is going on.
>> In a terminal, if I enter
>> ls {a*,b*}
>> I see all files beginning with a or b (I know this is not the best way
>> of doing that but it is a simple example of the problem I am seeing).
>> If I put that line in a file test.sh, make it executable, and then type
>> ./test.sh
>> then I see the same result.  However if at the start of test.sh I put the line
>> #!/usr/bin/env sh
>> at the start of test.sh and then run it I get
>> ls: cannot access {f*,l*}: No such file or directory
>>
>> It seems that brace expansion is not being performed in this case.  If
>> I just use wildcards it is ok, it is the braces that cause the
>> problem.  In order to determine whether a different shell was running
>> for some reason I also put
>> finger -l
>> in the script, and in both cases, with and without the shebang line,
>> it showed /bin/bash as the shell.
>
>     This is your login shell, not the shell running the script.

OK, looking at man finger again I see you are right.  I was mislead by
google, which is not unusual of course.

>
>> If, however, I put
>> #!/bin/bash
>> at the start then it works, still showing /bin/bash as the shell.
>>
>> Can someone explain what is going on?
>
>    If you do not put the shebang at the beginning of the script, then bash
>  executes it. If you put the shebang it is executed by what you say, i.e.
>  /usr/bin/env that calls sh. Try #!/usr/bin/env bash

I see, I don't now know where I got into the habit of putting
usr/bin/env sh there.  Somehow I had understood that as the
conventional thing to do.  ls -al /bin/sh shows that this is a link to
dash.  Why does dash not do brace expansion I wonder.

>
>       Hope this helps,

It certainly does, many thanks

Colin