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

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?

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}"

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

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"

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

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

Answer 6

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}"

Answer 7

#!/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?

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.

Answer 9

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