MDEV-15549 - wsrep_sst_common: fix per shellcheck

[grooverdan]

POSIX shell support in 10.0-galera would require f16ead5 however this shellcheck component wasn't included.

shellcheck -s sh wsrep_sst_common.sh

In wsrep_sst_common.sh line 258:
[ -n $3 ] && reval=$3
^-- SC2070: -n doesn't work with unquoted arguments. Quote or use [[ ]].
^-- SC2086: Double quote to prevent globbing and word splitting.

I submit this under the MCA.

[svoj]

Hi @grooverdan,

Thanks for your contribution. Corresponding JIRA task: https://jira.mariadb.org/browse/MDEV-15549

This task was added to 10.3 backlog.

Thanks,
Sergey

[janlindstrom]

Why you need double quote inside [] but not in reval= ?

[grooverdan]

because assignment isn't shell expanded

$ cat /tmp/x.sh
#!/bin/sh
a=$1
echo $1
$ /tmp/x.sh "a; ls"
a; ls

Expressions are:

$ cat /tmp/x.sh
#!/bin/sh
[ -n $1 ] && echo onehorse
[ -n "$1" ] && echo twohorse

$ /tmp/x.sh dog
onehorse
twohorse

$ /tmp/x.sh ''
onehorse

$ /tmp/x.sh '"" || 1'
/tmp/x.sh: line 2: [: too many arguments
twohorse

So lets protect against all the odd things that could be used in config file variables.