From: Peter Stephenson <p.w.stephenson@ntlworld.com>
To: zsh-users@zsh.org
Subject: Re: Can I test if a parameter expansion has worked
Date: Thu, 15 Sep 2022 09:24:15 +0100 (BST) [thread overview]
Message-ID: <1026093540.752006.1663230255721@mail.virginmedia.com> (raw)
In-Reply-To: <f93d2561-a8d8-c952-2aeb-8bcf43eef1cb@rayninfo.co.uk>
> On 15/09/2022 08:34 zzapper <zsh@rayninfo.co.uk> wrote:
> # adding a prefix '_s' to an image name
>
> f=stuff.jpg;
>
> print ${f/%(#m).[pjg][npi]e#[gf]/_s$MATCH}
>
> stuff_s.jpg # good this is what i want
>
> # now pass 'bad' input
>
> f=stuff.txt;
>
> print ${f/%(#m).[pjg][npi]e#[gf]/_s$MATCH}
> stuff.txt # expansion has obviously left the input unchanged but can I
> test for that???
No, there's no way of telling if some expansion actually changed an
expression without actually testing the final result. The differences
between the cases (changed / not changed) are buried deep within the
shell and don't leave an obvious trace above --- and in any case given
how complicated zsh expressions can get finding a useful binary way of
testing what the whole expression did would be incredibly hairy.
Just test the resulting expression.
pws
next prev parent reply other threads:[~2022-09-15 8:25 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-14 10:03 zzapper
2022-09-14 18:36 ` Bart Schaefer
2022-09-15 0:08 ` Alex Satrapa
2022-09-15 7:34 ` zzapper
2022-09-15 8:24 ` Peter Stephenson [this message]
2022-09-15 8:38 ` zzapper
2022-09-15 16:48 ` Bart Schaefer
2022-09-20 7:14 ` david rayner
2022-09-16 0:41 ` Alex Satrapa
2022-09-20 12:49 ` Stephane Chazelas
2022-09-20 13:25 ` Stephane Chazelas
2022-09-20 13:31 ` Stephane Chazelas
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