On Tue, Apr 21, 2015 at 2:44 PM, Dr Alun J. Carr <alun.j.c...@runbox.com>
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:
> 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 ???
>
> 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++))
--
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