On Fri, Aug 6, 2010 at 5:40 AM, Ralf Goertz wrote:
>> Bash Version: 4.0
>> Patch Level: 35
>> Release Status: release
>>
>> Description:
>>
>> I am used to setting variables in front of a command
>> like in
>>
>>> LANG=C man mplayer
>>
>> However, I get a "bash: syntax error near unexpected
>> token `do'" error when trying:
>>
>>> FOO=BAR while read a b; do echo $a $b; done
>>
>> Why? The similar
>>
>>> FOO=BAR read a b && echo $a $b
>>
>> works fine. (The problem occurred when I tried to
>> temporarily set IFS to the tab character for a "read").
On Fri, 2010-08-06 13:16:57 -0500, Dennis Williamson wrote:
> while is a compound command. Only simple commands can
> have preceding variable assignments. From man bash:
>
> The environment for any simple command or function may
> be augmented temporarily by prefixing it with parameter
> assignments, as described above in PARAMETERS. These
> assignment statements affect only the environment
> seen by that command.
At first glance, it seems to me that this is an arbitrary
distinction; would there not be a benefit in allowing
compound commands to serve in many of the same contexts
as simple commands?
For instance, according to:
info bash 'Basic Shell Features' 'Shell Commands' 'Compound Commands'
we already have:
Any redirections associated with a compound command
apply to all commands within that compound command
unless explicitly overridden.
Thus (with `process subsitution' available):
$ { read f; read g; printf "$f\n===\n$g\n"; } < <(printf 'Hello\nWolrd!\n')
Hello
===
Wolrd!
Wouldn't it be useful to extend other constructs to
compound commands?
Interestingly, according to:
info bash 'Basic Shell Features' 'Shell Commands' Pipelines
we have:
A `pipeline' is a sequence of simple commands separated
by one of the control operators `|' or `|&'.
and according to:
info bash 'Basic Shell Features' 'Shell Commands' Lists
we have:
A `list' is a sequence of one or more pipelines
separated by one of the operators `;', `&', `&&', or
`||', and optionally terminated by one of `;', `&', or a
`newline'.
However, compound commands already seem to work in these
contexts:
$ printf 'Hello\nWolrd!\n' | { read f; read g; printf "$f\n===\n$g\n"; }
Hello
===
Wolrd!
and:
$ { false; } && Hmmmm || echo OK
OK
At least the bash documentation should be updated
to reflect these facts.
Sincerely,
Michael Witten
