'delta_oligo_combined.bedgraph' 文件怎么可能在目录中并且 cat 命令看不到?OSX 拼写错误?
$ type=oligo
$ file_type=combined
$ ls delta_oligo_combined.bedgraph
delta_oligo_combined.bedgraph
$ cat delta_$(type)_$(file_type).bedgraph
-bash: file_type: command not found
cat: delta__.bedgraph: No such file or directory