Expand part of the path in bash script

Question

I am trying to list all files located in specific sub-directories of a directory in my bash script. Here is what I tried.

root_dir="/home/shaf/data/"
sub_dirs_prefixes=('ab' 'bp' 'cd' 'cn' 'll' 'mr' 'mb' 'nb' 'nh' 'nw' 'oh' 'st' 'wh')

ls "$root_dir"{$(IFS=,; echo "${sub_dirs_prefixes[*]}")}"rrc/"

Please note that I do not want to expand value stored in $root_dir as it may contain spaces but I do want to expand sub-path contained in {} which is a comma delimited string of contents of $sub_dirs_prefixes. I stored sub-directories prefixes in an array variable, $sub_dirs_prefixes , because I have to use them later on for something else.

I am getting following error:

ls: cannot access /home/shaf/data/{ab,bp,cd,cn,ll,mr,mb,nb,nh,nw,oh,st,wh}rrc/

If I copy the path in error message and run ls from command line, it does display contents of listed sub-directories.

Brace expansion happens before variable expansion, so this isn't possible in one pass. You could eval with all the security/reliability implications that has, but you'd be better off using a loop or array substitution. — that other guy
– that other guy, Commented Dec 9, 2016 at 19:42

chepner · Accepted Answer · 2016-12-09 20:00:57Z

1

You can command substitution to generate an extended pattern.

shopt -s extglob
ls "$root_dir"/$(IFS="|"; echo "@(${sub_dirs_prefixes[*]})rrc")

By the time parameter can command substitutions have completed, the shell sees this just before performing pathname expansion:

ls "/home/shaf/data/"/@(ab|bp|cd|cn|ll|mr|mb|nb|nh|nw|oh|st|wh)rrc

The @(...) pattern matches one of the enclosed prefixes.

It gets a little trickier if the components of the directory names contain characters that need to be quoted, since we aren't quoting the command substitution.

answered Dec 9, 2016 at 20:00

chepner

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1 Comment

shaffooo Over a year ago

Thanks for the answer. Can you please explain a little how extglob works so that i can accept your answer? Also you may want to remove / before @. You said @ matches one of the enclosed prefixes even though it matches each of those when I tried and returning correct result.

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