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Re: discrepancy with variable assignments and simple commands between sh
Re: discrepancy with variable assignments and simple commands between sh and bash
Wed, 25 Aug 2010 07:39:26 +0200
Mozilla-Thunderbird 188.8.131.52 (X11/20100329)
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
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 ;).
Okay, I think I found something
- 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
- Bash in POSIX-mode respects it