6

There is a script:

#!/bin/bash

s='1 2,   3   4,'
s0="$(echo ${s//,/ }|tr -s ' ')"
echo "s0: $s0"
d="'${s0//+([[:space:]])/"' '"}'"
echo "d: $d"

When I run this script output is:

$ ./test.sh
s0: 1 2 3 4
d: '1 2 3 4'

When I run the commands one by one in bash prompt, the $d variable is displayed properly:

$ s='1 2,   3   4,'
$ s0="$(echo ${s//,/ }|tr -s ' ')"
$ echo "s0: $s0"
s0: 1 2 3 4
$ d="'${s0//+([[:space:]])/"' '"}'"
$ echo "d: $d"
d: '1' '2' '3' '4'
$

Commands are run in bash:

$ type bash
bash is /bin/bash
$ echo $0
-bash

Why the $d during script run is set to '1 2 3 4' and not as expected '1' '2' '3' '4' ?

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1 Answer 1

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14

Extended globs like +(...) aren't enabled in Bash by default, you'll need to explicitly use shopt -s extglob in the script to enable them.

Your interactive shell probably has extglob enabled (in some startup file), so the substitution command works as expected when you try it on the command line. But in the script, most startup files are not read, extglob is left disabled, and the plus and parentheses are taken as literal characters. The character class works the same in both, so something like +( ) would match the pattern when extglob is off.

Here, the pattern doesn't match anything, there's no replacement and the only change you get in d are the single quotes you add around the ${s0//...} expansion.

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