report the samplename(s) from a bam using the read-group info.
Usage: goleft samplename [--errormulti] BAM
Positional arguments:
BAM bam for to get sample name(s)
Options:
--errormulti, -e return an error if there is not exactly 1 sample in the bam.
--help, -h display this help and exit
--version display version and exit