Correct way of building variable length argument line to external command in bash

Question

I need to use "find" command to find several different sets of files in my Bash function, depending on my script input.

So, I have thing like:

DAYS=30
case $1 in
A1) ARGLINE="-name 'FOO*.xml' -or -name 'BAR*.xml' -or -name 'BTT*.txt'"
    ;;
A2) ARGLINE="-name 'PO*xml' -or -name 'PR*xml'"
    ;;
...
esac
find . -maxdepth 1 -type f -mtime +${DAYS} `${ARGLINE}`

This works.

However, as soon as I want to use variable for number of days to search back to, like this:

DAYS=30
case $1 in
A1) ARGLINE="-name 'FOO*.xml' -or -name 'BAR*.xml' -or -name 'BTT*.txt'"
    ;;
A2) ARGLINE="-name 'PO*xml' -or -name 'PR*xml'"
    ;;
...
esac
if [[ $# -gt 1 ]]; then
    DAYS=$2
fi
find . -maxdepth 1 -type f -mtime +${DAYS} `${ARGLINE}`

The function fails when find doesn't find any files matching, with the following error:

No command '-name' found, did you mean: Command 'uname' from package 'coreutils' (main) -name: command not found

It however works correctly, when the number of days is such that find finds some files. It also fails when I try to pipe the output of succesful run into another command.

How should I correctly build the argument line for "find"?

Answer 1

In bash, use an array:

args=( '(' -name 'FOO*.xml' -or -name 'BAR*.xml' -or -name 'BTT*.txt' ')' )

The extra parentheses are there for creating the correct boolean logical grouping since you use -or).

Then, in the find command:

find ...some arguments... "${args[@]}"

You have an additional issue in that you use

`$ARGLINE`

This is a command substitution, similar to $( $ARGLINE ) and the shell will try to execute $ARGLINE (its value) as a command. This is why you get "No command '-name' found". The command substitution fails, but the find runs, which is why you think it "works".

Answer 2

The main issue here, is that quotes don't work inside quotes: after expanding a variable, the quotes inside it are just ordinary characters, e.g.:

$ foo='foo "bar doo"'
$ printf "<%s>\n" $foo
<foo>
<"bar>
<doo">

You should use an array to store command arguments like that:

ARGS=(-name 'FOO*.xml' -or -name 'BAR*.xml' -or -name 'BTT*.txt')

The shell will process quoting at this stage, and store distinct shell words as distinct array elements. Use the array like this:

find . "${ARGLINE[@]}"

If you want or need to, you can build the array piece by piece, this should result in the same array:

ARGS=(-name 'FOO*.xml')
ARGS+=(-or -name 'BAR*.xml')
ARGS+=(-or -name 'BTT*.txt')

---

However, note that you also used backticks to "quote" ${ARGLINE}. That will start a command substitution and run the contents of ARGLINE as a command. That's where your error comes from, the shell tries to run a program called -name.

---

Actually, in your example, you don't need an array, since you don't have any whitespace within the arguments. The main issue here usually is that the difference between whitespace between the arguments, and the whitespace within the arguments gets lost when the command line is stored to a string. But in your case, this might work, not that I'd recommend it:

set -f       # disable globbing
ARGLINE="-name FOO*.xml -or -name BAR*.xml -or -name BTT*.txt"
find . $ARGLINE