Re: discrepancy with variable assignments and simple commands between sh and bash

[Jan Schampera]

Mike Frysinger wrote:
> On Wednesday, August 25, 2010 00:59:58 Jan Schampera wrote:
> > Mike Frysinger wrote:
> > > the difference here being the value in variable "a" after function "f"
> > > finishes executing.  i was expecting the behavior of `bash`, not of `sh`.
> > >  i cant seem to find anything covering this in the man page except for
> > > perhaps interpreting the meaning of some sections to mean this behavior
> > > is allowed. but i certainly didnt locate anything that would imply
> > > behavior of this would differ across bash and sh ...
> > I'd expect "VAR=VAL <simple command>" to behave like in your "bash"
> > example, in any case (i.e. also for functions!). Just intuitively, I
> > mean. I don't know any standard documents about it, maybe it is
> > "implementation defined", as so often.
> >
> > Dash behaves the same way as your "sh" example, Korn too. Z behaves like
> > the "bash" example here. So I fear it actually isn't standardized and
> > you can't operate with functions the same way you operate with separate
> > processes.
>
> unfortunately, ive relied on this bash behavior in the past in bash-specific 
> scripts because it's an easy way of tweaking a variable's value for a specific 
> command without having to save/restore context.  which is why i was surprised 
> when it didnt work in a #!/bin/sh script (which had sh->bash).  not that 
> standards bodies care about the pains they inflict upon me ;).
> -mike


Okay, I think I found something

[POSIX excerpts]
- When a function is executed, it shall have the syntax-error and 
variable-assignment properties described for special built-in utilities 
in the enumerated list at the beginning of Special Built-In Utilities .
- Variable assignments specified with special built-in utilities remain 
in effect after the built-in completes; this shall not be the case with 
a regular built-in or other utility.

[Bash docs about POSIX mode]
 24. Assignment statements preceding shell function calls persist in the
     shell environment after the function returns, as if a POSIX
     special builtin command had been executed.

Conclusion (still waiting for the Austin Group undercover guy):
- POSIX specifies this behaviour
- Bash in Bash-mode overrides this (which results in intuitive 
behaviour, IMHO)
- Bash in POSIX-mode respects it


J.