Re: Problem with brace expansion
On Thu, Apr 23, 2015 at 01:01:43AM +0100, Dr Alun J. Carr wrote: > Well, to be strictly conformant with heirloom SysV sh, Nobody cares about compatibility with Bourne shell any more. Not since Solaris finally pulled its head out of its ass and put a POSIX sh in /bin (20 years after everyone else). > Perhaps this needs to go into a FAQ somewhere about coding loops for an > absolutely bare-bones shell. You are on bug-bash, so all we really care about is bash. Or maybe POSIX. Or more specifically, bash's conformance with POSIX. If you want a FAQ, though, I have one for this: http://mywiki.wooledge.org/BashPitfalls#pf33 OK, technically it's not in the FAQ, but close enough.
Re: Problem with brace expansion
Well, to be strictly conformant with heirloom SysV sh, we have to use the following (which is uglier than Cobol with a hangover): #looper2-sh.sh n=4 i=1 while [ $i -le $n ] do echo i = $i i=`expr $i + 1` done which also works with dash and mksh. Perhaps this needs to go into a FAQ somewhere about coding loops for an absolutely bare-bones shell. > On 22 Apr 2015, at 00:22, Eric Blake wrote: > > On 04/21/2015 01:44 PM, Dr Alun J. Carr wrote: > >> Tests were done with bash, ksh, zsh, pdksh, dash and heirloom System V >> Bourne sh with the following versions: >> bash 3.2.57(1) >> bash 4.3.33(1) >> ksh version sh (AT&T Research) 93u+ 2012-08-01 >> zsh 5.0.5 (x86_64-apple-darwin14.0) >> pdkshstable 5.2.14 >> dash stable 0.5.8 >> sh ??? > > You do realize, I hope, that brace expansion is not required by POSIX, > and therefore there is no standard for what behavior it has, and it > should be no surprise that pdksh, dash, and Bourne sh do not try to > expand it. > > As for whether bash should expand $n into 4 prior to doing brace > expansion, or whether brace expansion is attempted first but not > recognizing $n as a valid bound devolves into no expansion, that is > indeed a difference between ksh and bash. But bash is consistent with > its documentation: > >> The order of expansions is: brace expansion; tilde expansion, parameter >> and variable expansion, arithmetic expansion, and command substitution >> (done in a left-to-right fashion); word splitting; and pathname expan‐ >> sion. > > so you cannot use a variable as a bound and still expect brace expansion > to work, since variables aren't expanded yet. > > -- > Eric Blake eblake redhat com+1-919-301-3266 > Libvirt virtualization library http://libvirt.org > signature.asc Description: Message signed with OpenPGP using GPGMail
Re: Problem with brace expansion
On 04/21/2015 01:44 PM, Dr Alun J. Carr wrote: > Tests were done with bash, ksh, zsh, pdksh, dash and heirloom System V Bourne > sh with the following versions: > bash 3.2.57(1) > bash 4.3.33(1) > ksh version sh (AT&T Research) 93u+ 2012-08-01 > zsh 5.0.5 (x86_64-apple-darwin14.0) > pdksh stable 5.2.14 > dash stable 0.5.8 > sh??? You do realize, I hope, that brace expansion is not required by POSIX, and therefore there is no standard for what behavior it has, and it should be no surprise that pdksh, dash, and Bourne sh do not try to expand it. As for whether bash should expand $n into 4 prior to doing brace expansion, or whether brace expansion is attempted first but not recognizing $n as a valid bound devolves into no expansion, that is indeed a difference between ksh and bash. But bash is consistent with its documentation: >The order of expansions is: brace expansion; tilde expansion, parameter >and variable expansion, arithmetic expansion, and command substitution >(done in a left-to-right fashion); word splitting; and pathname expan‐ >sion. so you cannot use a variable as a bound and still expect brace expansion to work, since variables aren't expanded yet. -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature
Re: Problem with brace expansion
On Tue, Apr 21, 2015 at 2:44 PM, Dr Alun J. Carr
wrote:
> There appears to be a bug in bash when using a variable in curly brace
> expansion, e.g., {1..$n}. I have put the two following test scripts in the
> attached files looper1.sh and looper2.sh:
>
> #looper1.sh
> for i in {1..4}
> do
> echo i = $i
> done
>
> #looper2.sh
> n=4
> for i in {1..$n}
> do
> echo i = $i
> done
>
> Tests were done with bash, ksh, zsh, pdksh, dash and heirloom System V
> Bourne sh with the following versions:
> bash3.2.57(1)
> bash4.3.33(1)
> ksh version sh (AT&T Research) 93u+ 2012-08-01
> zsh 5.0.5 (x86_64-apple-darwin14.0)
> pdksh stable 5.2.14
> dashstable 0.5.8
> sh ???
>
> Results for bash (both versions give the same result); note that bash
> fails to expand the curly brace expression in only the second case:
>
> $ bash looper1.sh
> i = 1
> i = 2
> i = 3
> i = 4
>
> $ bash looper2.sh
> i = {1..4}
>
> Repeating using ksh we get correct expansion of the curly braces:
>
> $ ksh looper1.sh
> i = 1
> i = 2
> i = 3
> i = 4
>
> $ ksh looper2.sh
> i = 1
> i = 2
> i = 3
> i = 4
>
> And using zsh, the same result as for ksh:
>
> $ zsh looper1.sh
> i = 1
> i = 2
> i = 3
> i = 4
>
> $ zsh looper2.sh
> i = 1
> i = 2
> i = 3
> i = 4
>
> Neither pdksh (which installs as ksh using homebrew) nor dash handle
> either case correctly:
>
> pdksh:
>
> $ /usr/local/bin/ksh looper1.sh
> i = {1..4}
>
> $ /usr/local/bin/ksh looper2.sh
> i = {1..4}
>
> dash:
>
> $ dash looper1.sh
> i = {1..4}
>
> $ dash looper2.sh
> i = {1..4}
>
> The System V sh from the heirloom project behaves the same way as pdksh
> and dash (or more correctly, since System V is really the reference, pdksh
> and dash behave the same way as SysV sh):
>
> $ 5 sh looper1.sh
> i = {1..4}
>
> $ 5 sh looper2.sh
> i = {1..4}
>
>
>
Bash performs brace expansion before variable expansion and thus does not
support the feature that zsh and ksh have which do variable expansion
before brace expansion.
To use a variable, use C-style for loops:
for ((i = 1; i <= 4; i++))
--
Visit serverfault.com to get your system administration questions answered.
Re: Problem with brace expansion
On Tue, 21 Apr 2015, Dr Alun J. Carr wrote:
There appears to be a bug in bash when using a variable in curly
brace expansion, e.g., {1..$n}. I have put the two following test
scripts in the attached files looper1.sh and looper2.sh:
Brace expansion is done before variable expansion:
The order of expansions is: brace expansion; tilde expansion,
parameter and variable expansion, arithmetic expansion, and
command substitution (done in a left-to-right fashion); word
splitting; and pathname expansion.
Neither pdksh (which installs as ksh using homebrew) nor dash handle either
case correctly:
Neither pdksh nor dash has brace expansion.
--
Chris F.A. Johnson,
Problem with brace expansion
There appears to be a bug in bash when using a variable in curly brace
expansion, e.g., {1..$n}. I have put the two following test scripts in the
attached files looper1.sh and looper2.sh:
#looper1.sh
for i in {1..4}
do
echo i = $i
done
#looper2.sh
n=4
for i in {1..$n}
do
echo i = $i
done
Tests were done with bash, ksh, zsh, pdksh, dash and heirloom System V Bourne
sh with the following versions:
bash3.2.57(1)
bash4.3.33(1)
ksh version sh (AT&T Research) 93u+ 2012-08-01
zsh 5.0.5 (x86_64-apple-darwin14.0)
pdksh stable 5.2.14
dashstable 0.5.8
sh ???
Results for bash (both versions give the same result); note that bash fails to
expand the curly brace expression in only the second case:
$ bash looper1.sh
i = 1
i = 2
i = 3
i = 4
$ bash looper2.sh
i = {1..4}
Repeating using ksh we get correct expansion of the curly braces:
$ ksh looper1.sh
i = 1
i = 2
i = 3
i = 4
$ ksh looper2.sh
i = 1
i = 2
i = 3
i = 4
And using zsh, the same result as for ksh:
$ zsh looper1.sh
i = 1
i = 2
i = 3
i = 4
$ zsh looper2.sh
i = 1
i = 2
i = 3
i = 4
Neither pdksh (which installs as ksh using homebrew) nor dash handle either
case correctly:
pdksh:
$ /usr/local/bin/ksh looper1.sh
i = {1..4}
$ /usr/local/bin/ksh looper2.sh
i = {1..4}
dash:
$ dash looper1.sh
i = {1..4}
$ dash looper2.sh
i = {1..4}
The System V sh from the heirloom project behaves the same way as pdksh and
dash (or more correctly, since System V is really the reference, pdksh and dash
behave the same way as SysV sh):
$ 5 sh looper1.sh
i = {1..4}
$ 5 sh looper2.sh
i = {1..4}
looper1.sh
Description: Binary data
looper2.sh
Description: Binary data
