Date: Mon, 14 Mar 2011 02:39:49 -0430 From: Andres Perera <andres.p@zoho.com> To: Maxim Khitrov <max@mxcrypt.com> Cc: FreeBSD <freebsd-questions@freebsd.org> Subject: Re: Shell script termination with exit function in backquotes Message-ID: <AANLkTikH%2Bn%2BuTDokiFSKKQ%2BsfkFFm6NLaFatfwOxVSQ=@mail.gmail.com> In-Reply-To: <AANLkTi=-CFmxRicGcosvzhBbM3DMjbWwQNirMrJ1_KP=@mail.gmail.com> References: <AANLkTi=-CFmxRicGcosvzhBbM3DMjbWwQNirMrJ1_KP=@mail.gmail.com>
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ash tries to overoptimize by running certain command substitutions
without a subshell
On Sun, Mar 13, 2011 at 7:56 PM, Maxim Khitrov <max@mxcrypt.com> wrote:
> Hello everyone,
>
> I might be doing something dumb here, but this doesn't make sense to
> me. When I run the following script, I would expect to see no output:
>
> ----
> #!/bin/sh
>
> exit_prog()
> {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0echo -n 'before'
> =C2=A0 =C2=A0 =C2=A0 =C2=A0exit 0
> =C2=A0 =C2=A0 =C2=A0 =C2=A0echo -n 'after'
> }
>
> echo line 1: `exit_prog`
> echo line 2:
> echo line 3: `exit 1`
> echo line 4:
> ----
>
> The reason I expect to see no output is because 'exit 0' should be
> called before any of the echo lines are allowed to execute. Instead,
> what I get on FreeBSD 7 & 8 is:
>
> ----
> line 1: before
> line 2:
> ----
>
> I don't understand this because 'exit 0' seems to terminate the call
> to 'exit_prog', but the execution of the script continues. However,
> when 'exit 1' is called, the script terminates before printing out the
> last 2 lines.
>
> It seems that 'exit' inside a function doesn't work when that function
> is called with backquotes. I assume it has something to do with the
> fact that commands in backquotes are executed in a sub-shell, but the
> behavior is inconsistent.
>
> When I run the same script on RHEL using bash, all 4 lines are printed:
>
> ----
> line 1: before
> line 2:
> line 3:
> line 4:
> ----
>
> What's going on here?
>
> - Max
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