Samtools Depth Option For More Than One Bam Files
The usage says that you can link multiple files, make sure the specify the options before the bam files
Usage: samtools depth [options] in1.bam [in2.bam [...]]
Options:
-b <bed> list of positions or regions
-f <list> list of input BAM filenames, one per line [null]
-l <int> minQLen
-q <int> base quality threshold
-Q <int> mapping quality threshold
-r <chr:from-to> region
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