Bash: Brace expansion in scripts not working due to unwanted escaping

Question

I want to do something like this in a bash script. I'm using bash 4.1.10.

# rm -rf /some/path/{folder1,folder2,folder3}

Works nicely (and as expected) from the shell itself. It deletes the 3 desired folders leaving all others untouched.

When I put it into script something unwanted happens. For example, my script:

#!/bin/bash
set -x
VAR="folder1,folder2,folder3"
rm -rf /some/path/{$VAR}

When I execute this script, the folders are not deleted.

I think this is due to the fact that some unwanted quoting is occurring. Output from the script using #!/bin/bash -x:

rm -rf '/some/path/{folder1,folder2,folder3}'

which of course cannot succeed due to the ' marks.

How can I get this working within my script?

Dresden

Do you absolutly want to use {}-expansion, or is an equivalent alternative ok? – Averroism

sure.. I just have a list of subfolder names I want to remove in ONE concrete subshell in background -means more concrete: rm -rf /some/path/{folder1,folder2,folder3} & not a loop which runs over each subfolder doing this as this would increase fileserver load – Dresden

Answer 1

According to the man page:

The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion.

So to get around this, add another level of expansion:

eval "rm -rf /some/path/{$VAR}"

Guidepost

How to get around brace expansion, though? – Protestation

function sort-note() { mv "$1"{,\;Sorted}; }. Eg, like in maildir, but for my own purposes? – Protestation

At command line: mv foo.note{,\;Sorted}; ls foo.note* # foo.note;Sorted – Protestation

Answer 2

Since you're writing a script, there's no reason to write hard-to-maintain code using eval tricks

VAR="f1,f2,f3"
IFS=,
set -- $VAR
for f; do
  rm -r "/path/to/$f"
done

or

VAR=( f1 f2 f3 )
for f in "${VAR[@]}"; do 
  rm -r "/path/to/$f"
done

Logion

Answer 3

No, it's due to the fact that brace expansion happens before parameter expansion. Find another way of doing this, such as with xargs.

xargs -d , -I {} rm -rf /some/path/{} <<< "$VAR"

Gilded

Answer 4

If your code can be rearranged, you can use echo and command substitution in bash. Something like this:

#!/bin/bash
set -x
VAR=`echo /some/path/{folder1,folder2,folder3}`
rm -rf $VAR

Assembler

Answer 5

You need to enable braceexpand flag:

#!/bin/bash
set -B
for i in /some/path/{folder1,folder2,folder3}
do
  rm -rf "$i"
done

Octavie

DOesn't seem to work for me. (Note that the "/some/path/{folder1,folder2,folder3}" string is stored in a variable; if you enter the above literally in a shell it will work because the shell does the expansion, but it's of no use in a script.) – Catholicity

But if you know the actual literal list of things you want to do brace expansion of, then it would work: for i in ${prefix}{fixed,list,of,literal,strings}${suffix} would loop over 5 strings, with ${prefix} and ${suffix} properly substituted. – Catholicity

Fixed the answer. You need to set -B / braceexpand with set, or provide it as a bash parameter :) – Octavie

No, still doesn't work. I don't think you understand the question: suppose you have a variable, like VAR="/tmp/{folder1,folder2,folder3}". Now you want to create (say) the corresponding directories, using $VAR. How do you do it? (If you don't have it in a var and can just type it directly, then everything is fine, as I said in my second comment above.) – Catholicity

Answer 6

#!/bin/bash
set -x
VAR="folder1,folder2,folder3"
eval "rm -rf /some/path/{$VAR}"

---

Edit The remainder is just for info. I try to be informative, but not wordy :_)

Recent bashes have the globstar option. This might perhaps come in handy in the future

shopt -s globstar
rm -rfvi some/**/folder?

Beatabeaten

i my concrete case I do not have folder1,folder2,folder3 but complete different names. Put for this special example this would have worked. – Dresden

@Roland: I'm really mentioning globstar which I guess you didn't know yet. You did notice the answer (you know, the first part)? – Beatabeaten

Answer 7

The problem is not that in script mode some unwanted quoting is happening but that you put the folder names into a variable and the variable content is expanded after the brace expansion is done.
If you really want to do it like this you have to use eval:

eval "rm -rf /some/path/{$VAR}"

Groovy

Answer 8

Another trick you can use (instead of the dangerous eval) is just plain echo inside a subshell. This works, for instance:

paths=`echo /some/path/{folder1,folder2,folder3}`
echo rm -rf $paths

outputs:

rm -rf /some/path/folder1 /some/path/folder2 /some/path/folder3

as desired. (Remove the "echo" in the second line, to make it actually do the rm.)

---

The crucial point is that bash does brace expansion before parameter expansion, so you never want to put a comma-separated list (surrounded by braces or not) into a variable -- if you do, then you'll have to resort to eval. You can however put a list of space-separated strings into a variable, by having the brace expansion happen in a subshell before assignment.

Catholicity

Answer 9

replace {$VAR} by ${VAR} :-)

Hammered

I want braces to be generated about the content of $VAR not brace expansion of $VAR – Dresden