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From: Thorsten Kampe <thorsten@thorstenkampe.de>
Subject: Re: Negative length parameter expansion
Date: Sun, 12 Apr 2015 13:43:24 +0200
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References: <mgd6pj$ioh$1@ger.gmane.org> <2421271428831232@web29o.yandex.ru>
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* ZyX (Sun, 12 Apr 2015 12:33:52 +0300)
> 
> 12.04.2015, 10:47, "Thorsten Kampe" <thorsten@thorstenkampe.de>:
> > Hi,
> >
> > Bash got negative length parameter expansion (like in `${STRING:11:-
> > 17}`) in version 4.2 and Zsh in 4.3.12.
> >
> > How would I do negative length parameter expansion in Bash or Zsh if
> > my version doesn't support it?
> 
> `$#STRING` is a length of the string. `-17` is `$(( ${#STRING}-17+1 ))`. (`$(( ))` may be not necessary, most likely they will not be necessary in zsh, don’t know about bash). `${#PARAMETER}` form is supported by any POSIX shell (but not `$#PARAMETER` without figure braces).

Simple and elegant solution, thanks.

Just for correctness: your solution has an off-by-one error (actually 
an "off by offset" error). Offset starts at 0. You're adding 1 but 
you would have to subtract 0 (or in general: offset).

Following the example from
<http://wiki.bash-hackers.org/syntax/pe#negative_length_value>

```
MYSTRING="Be liberal in what you accept, and conservative in what you 
send"
offset=11
length=17

printf "${MYSTRING:$offset:-$length}\n"
in what you accept, and conservative

length=$((${#MYSTRING} - offset - length))
printf "${MYSTRING:$offset:$length}\n"
in what you accept, and conservative
```

Thorsten