Date: Tue, 22 Mar 2011 18:07:13 -0700 From: Devin Teske <dteske@vicor.com> To: RW <rwmaillists@googlemail.com> Cc: freebsd-questions@freebsd.org Subject: Re: Shell script termination with exit function in backquotes Message-ID: <1300842433.5368.2.camel@dt.vicor.com> In-Reply-To: <20110322123243.1257e695@gumby.homeunix.com> References: <AANLkTi=-CFmxRicGcosvzhBbM3DMjbWwQNirMrJ1_KP=@mail.gmail.com> <759A467E-407A-4DB8-9756-08011B5405F0@vicor.com> <AANLkTi=CXLFUBhnY1LuhkeUiGHHGZ43yd%2BMYE9L50_O4@mail.gmail.com> <AANLkTimrnV2rJLyc3M4e3gGy_GUDLXp128f6n8svM3_g@mail.gmail.com> <AANLkTim0GvnAyK3%2B=Bd1Sr=maz0B3Ybgve_c6FKWwfNs@mail.gmail.com> <AANLkTimWxiRQNG3Um__kY-6%2BQ59g5yZT-Kt0qLAqTWOO@mail.gmail.com> <EFA32C5B-1892-41C3-B34B-F96E75CA72CA@vicor.com> <20110322123243.1257e695@gumby.homeunix.com>
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On Tue, 2011-03-22 at 12:32 +0000, RW wrote:
> On Sat, 19 Mar 2011 09:44:57 -0700
> Devin Teske <dteske@vicor.com> wrote:
>
>
> > At least two variations to the rule that { ... } is a block of
> > commands executed in the current shell are:
> >
> > 1. When the block appears as a function
>
> Is that correct?
It depends on where and how you are using the function.
For example, ...
#!/bin/sh
: ============
abc()
{
x=2
}
: ============
x=1
abc
echo $x
# produces "2"
: ============
x=1
: `abc`
echo $x
# produces "1"
: ============
x=1
: `x=2`
echo $x
# produces "2"
: ============
x=1
: `{ x=2; }`
echo $x
# produces "2"
: ============
... in the above example, the function embedded within back-ticks is
executed in a sub-shell (but that is not to imply that back-ticks
themselves invoke a sub-shell -- as shown above, I put a simple
statement and a compound statement [surrounded in curlies] in back-ticks
and neither are executed in a sub-shell... only the function-call is
executed within a sub-shell when executed within back-ticks).
> I'd assumed that functions do execute in the current
> shell since you can alter variables from a function
Functions may or may-not execute in a sub-shell depending on the context
in which they are used.
> , whilst you can't
> from a "()".
Correct, parenthesetical blocks always form a sub-shell.
>
> e.g.
> --------------------------------------------------------------------
> $ cat /tmp/foo
> #!/bin/sh
>
> f (){
> x=2
> }
>
> x=1
> f
> echo $x
> ( x=3 )
> echo $x
>
> --------------------------------------------------------------------
>
> $ /tmp/foo
> 2
> 2
>
>
>
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--
Cheers,
Devin Teske
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