listing directory contents with xargs and grep

Question

I have a directory with lots of json and pdf files that are named in a pattern. I am trying to filter the files on name with the following pattern \d{11}-\d\.(?:json|pdf) in the command. For some reason it is not working. I believe it is due the fact that the xargs take the arguments one big line of string or when the input is split there is some whitespace, \n or null character.

ls | xargs -d '\n' -n 1 grep '\d{11}-\d\.(?:json|pdf)'

if I try just this ls | xargs -d '\n' -n 1 grep '\d' It selects file names with digits in them, as soon as I specify the multiplicity regex, nothing matches.

Answer 1

First, ls | xargs grep 'pattern' makes grep look for occurrences in contents of files listed by ls, not in list of filenames. To look for filenames it should be enough to do:

ls | grep 'pattern'

Second, grep '\d{11}-\d\.(?:json|pdf)' would work only with GNU grep and -P option. Use the following syntax instead - it works with GNU, busybox and FreeBSD implementations of grep:

ls | grep -E '[[:digit:]]{11}-[[:digit:]]\.(json|pdf)'

Third, parsing ls is not a good idea. Use GNU find:

find . -maxdepth 1 -regextype egrep -regex '.*/[[:digit:]]{11}-[[:digit:]]\.(json|pdf)'

or FreeBSD find:

find -E . -maxdepth 1 -regex '.*/[[:digit:]]{11}-[[:digit:]]\.(json|pdf)'

Answer 2

You don't need any of that complexity. Just use a shell glob. This one is for shells such as bash that understand {x,y} braced alternatives:

ls *[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]-[0-9].{json,pdf}

If you want to do something with the matched files, don't take the output of ls but just use the glob to iterate across the files directly.