CODEWITHSUNDEEP
bashwildcard
jaxreiff
jaxreiff

Reputation: 513

How to expand wildcards after substituting them into a filepath as arguments, in bash script?

I am currently trying to substitute arguments into a filepath

FILES=(~/some/file/path/${1:-*}*/${2:-*}*/*)

I'm trying to optionally substitute variables, so that if there are no arguments the path looks like ~/some/file/path/**/**/* and if there is just one, it looks like ~/some/file/path/arg1*/**/*, etc. However, I need the wildcard expansion to occur after the filepath has been constructed. Currently what seems to be happening is that the filepath is into FILES as a single filepath with asterisks.

The broader goal is to pass all subdirectories that are two levels down from the current directory into the FILES variable, unless arguments are given, in which case the first argument is used to pick a particular directory at the first level, the second argument for the second level.

edit:

This script generates directories and then grabs random files from them, and previously had ** instead of *, however it still works, and correctly restricts the files to pull from when given arguments. Issue resolved.

#!/bin/bash

mkdir dir1 dir1/a
touch dir1/a/foo.txt dir1/a/bar.txt
cp -r dir1/a dir1/b
cp -r dir1 dir2

files=(./*${1:-}/*/*)

for i in {1..10}
do
    # Get random file
    nextfile=${files[$RANDOM % ${#files[@]} ]}

    # Use file
    echo "$nextfile" || break

    sleep 0.5
done

rm -r dir1 dir2

Upvotes: 2

Views: 135

Answers (1)

Charles Duffy
Charles Duffy

Reputation: 295403

I can't reproduce this behavior.

$ files=( ~/tmp/foo/${1:-*}*/${2:-*}*/* )
$ declare -p files
declare -a files='([0]="/Users/chaduffy/tmp/foo/bar/baz/qux")'

To explain why this is expected to work: Parameter expansion happens before glob expansion, so by the time glob expansion takes place, content has already been expanded. See lhunath's simplified diagram of the bash parse/expansion process for details.

A likely explanation is simply that your glob has no matches, and is evaluating to itself for that reason. This behavior can be disabled with the nullglob switch, which will give you an empty array:

shopt -s nullglob
files=(~/some/file/path/${1:-*}*/${2:-*}*/*)
declare -p files

Another note: ** only has special meaning in shells where shopt -s globstar has been run, and where this feature (added in 4.0) is available. On Mac OS X (without installation of a newer version of bash via MacPorts or similar), it doesn't exist; you'll want to use find for recursive operations. If your glob would only match if ** triggered recursion, this would explain the behavior in question.

Upvotes: 4

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