* Negative length parameter expansion
@ 2015-04-12 7:27 Thorsten Kampe
2015-04-12 9:33 ` ZyX
0 siblings, 1 reply; 4+ messages in thread
From: Thorsten Kampe @ 2015-04-12 7:27 UTC (permalink / raw)
To: zsh-users
Hi,
Bash got negative length parameter expansion (like in `${STRING:11:-
17}`) in version 4.2 and Zsh in 4.3.12.
How would I do negative length parameter expansion in Bash or Zsh if
my version doesn't support it?
Thorsten
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Negative length parameter expansion
2015-04-12 7:27 Negative length parameter expansion Thorsten Kampe
@ 2015-04-12 9:33 ` ZyX
2015-04-12 11:43 ` Thorsten Kampe
0 siblings, 1 reply; 4+ messages in thread
From: ZyX @ 2015-04-12 9:33 UTC (permalink / raw)
To: Thorsten Kampe, zsh-users
12.04.2015, 10:47, "Thorsten Kampe" <thorsten@thorstenkampe.de>:
> Hi,
>
> Bash got negative length parameter expansion (like in `${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?
>
> Thorsten
`$#STRING` is a length of the string. `-17` is `$(( ${#STRING}-17+1 ))`. (`$(( ))` 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).
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Negative length parameter expansion
2015-04-12 9:33 ` ZyX
@ 2015-04-12 11:43 ` Thorsten Kampe
2015-04-12 11:54 ` ZyX
0 siblings, 1 reply; 4+ messages in thread
From: Thorsten Kampe @ 2015-04-12 11:43 UTC (permalink / raw)
To: zsh-users
* 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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Negative length parameter expansion
2015-04-12 11:43 ` Thorsten Kampe
@ 2015-04-12 11:54 ` ZyX
0 siblings, 0 replies; 4+ messages in thread
From: ZyX @ 2015-04-12 11:54 UTC (permalink / raw)
To: Thorsten Kampe, zsh-users
12.04.2015, 14:45, "Thorsten Kampe" <thorsten@thorstenkampe.de>:
> * 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).
Sorry, I was always using ${VAR[start,end]} form. My variant is correct for ${VAR[start,end]} (where `start` starts from one, not from zero), not for ${VAR:offset:length} which I never used (and thus for some reason was under impression that it was the other form of expressing the same thing).
Thanks for the correction.
>
> Following the example from
> <http://wiki.bash-hackers.org/syntax/pe#negative_length_value>
>
> ```
> MYSTRING="Be liberal in what you accept, and conservative in what you
> send"
> offset=11
> length=17
>
> printf "${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
^ permalink raw reply [flat|nested] 4+ messages in thread
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2015-04-12 7:27 Negative length parameter expansion Thorsten Kampe
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