Re: local variable assignment and pipelines?

[Peter Stephenson <pws@csr.com>]

Dan Nelson wrote:
> a=1 | echo $a      -> prints "1" on zsh, prints nothing on ash,pdksh,bash

It's an inevitable but unintended side effect of the way some
substitutions are done by the shell before it forks.  The list given in
subst.c is this one.

/* Do substitutions before fork. These are:
 *  - Process substitution: <(...), >(...), =(...)
 *  - Parameter substitution
 *  - Command substitution
 * Followed by
 *  - Quote removal
 *  - Brace expansion
 *  - Tilde and equals substitution
 */

My guess is this is left undefined by POSIX etc.  The stuff on pipelines
is fairly terse, but there might be something elsewhere since I didn't
look all that closely.

Where you would not want this to happen, and it doesn't, is if the
assignment immediately precedes a command.

pws


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