Bash script that calls a program with some asterisks in arguments

Question

I’ve spent last hour or so trying to write a pretty simple bash script and I never felt so dumb.

So I have a list of strings (which are package selector specifications for a package manager, if that matters) which might contain asterisks. I need to build a command line preserving those asterisks and then call a program. Here is my naïve attempt:

xs="foo/bar */*"

xs_cmd=""
for x in $xs; do
  xs_cmd="$xs_cmd  -0 $x "
done

echo $xs_cmd

I need the echo call to be equivalent to

echo   -0 foo/bar    -0 '*/*' 

which outputs -0 foo/bar -0 */*.

P. S. In reality the first line is slightly more complex: xs="$some foo/bar */* $(get_others)".

---

If you run this script in a directory containing a/b, you’ll get -0 foo/bar -0 a/b instead.

When I change the last line to

echo "$xs_cmd"  # note the quotes

I get -0 foo/bar -0 a/b and, first of all that’s not what I want, since now I’m invoking echo with a single argument, and furthermore that tells me that the expansion is happening earlier, likely in the for loop.

But I can’t change the for line because

for x in "$xs"; do  # note the quotes

will just make the loop iterate only once: -0 foo/bar */* (there is a single -0) so adding those quotes is not an option for sure.

Now if I revert back to the original script and replace the first line with

xs="foo/bar '*/*'"  # note additional single quotes

I get -0 foo/bar -0 '*/*' (single quotes should’t be there).

It seems that I tried every combination of quotes and backslash-escapes of asterisks and I have literally no idea what to do now.

Answer 1

I used your original script, but with single quotes on the first line (only) and it worked as I think you want it (-0 before each file path):-

xs='foo/bar */*'

xs_cmd=""
for x in $xs; do
  xs_cmd="$xs_cmd  -0 $x "
done

echo $xs_cmd

You will probably find problems when you come to use it if there are embedded blanks in any of the file paths. If so change the command in the loop to:-

  xs_cmd="$xs_cmd  -0 \"$x\" "

Answer 2

Depending on what you're trying to achieve, your either need to quote these */*:

xs="foo/bar '*/*'" #!

xs_cmd=""
for x in $xs ; do
    xs_cmd="$xs_cmd  -0 $x "
done

echo $xs_cmd
eval echo $xs_cmd
eval "echo $xs_cmd"

or use arrays, or both:

xs=("foo/bar" "*/*") #!

xs_cmd=""
for x in "${xs[@]}"; do
    xs_cmd="$xs_cmd  -0 '$x' " #!
done

echo "$xs_cmd"
eval "echo $xs_cmd"