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Re: Can I test if a parameter expansion has worked

X-seq: zsh-users 28106
From: Stephane Chazelas <stephane@xxxxxxxxxxxx>
To: zzapper <zsh@xxxxxxxxxxxxxx>
Cc: zsh-users@xxxxxxx
Subject: Re: Can I test if a parameter expansion has worked
Date: Tue, 20 Sep 2022 13:49:01 +0100
Archived-at: <https://zsh.org/users/28106>
In-reply-to: <f93d2561-a8d8-c952-2aeb-8bcf43eef1cb@rayninfo.co.uk>
List-id: <zsh-users.zsh.org>
Mail-followup-to: zzapper <zsh@xxxxxxxxxxxxxx>, zsh-users@xxxxxxx
References: <5dc8b935-f234-ca54-0ceb-50cb1da9bc29@rayninfo.co.uk> <f93d2561-a8d8-c952-2aeb-8bcf43eef1cb@rayninfo.co.uk>

2022-09-15 08:34:34 +0100, zzapper:
[...]
> 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???
[...]

You could always do:

unset flag
print -r -- ${f/%(#m).[pjg][npi]e#[gf]/_s$MATCH${flag=}}
if (( $+flag )) echo it did substitute

Note that "print $var" without the -- is a command injection
vulnerability and without -r generally not what you want.

-- 
Stephane

References:
- Can I test if a parameter expansion has worked
  - From: zzapper
- Re: Can I test if a parameter expansion has worked
  - From: zzapper

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