MariaDB Galera Cluster 10.2.12.

When using xtrabackup-v2 as the SST method and using a compressor like gzip or pigz, the following messages appear in the error logs:

/bin/wsrep_sst_common: line 274: [: pigz: binary operator expected
/bin/wsrep_sst_common: line 279: [: pigz: binary operator expected

For reference: http://galeracluster.com/documentation-webpages/xtrabackupoptions.html

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It appears to be a shell scripting error with the construction of the IF statement on the previously mentioned line numbers:

if [ -z $reval ]; then

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Could this be rewritten like this:

if [[ -z $reval ]]; then

using double brackets?