Tutorial :How to escape extended pathname expansion patterns in quoted expressions?


In addition to the basic *, ? and [...] patterns, the Bash shell provides extended pattern matching operators like !(pattern-list) ("match all except one of the given patterns"). The extglob shell option needs to be set to use them. An example:

~$ mkdir test ; cd test ; touch file1 file2 file3  ~/test$ echo *  file1 file2 file3  ~/test$ shopt -s extglob  # make sure extglob is set  ~/test$ echo !(file2)  file1 file3  

If I pass a shell expression to a program which executes it in a sub-shell, the operator causes an error. Here's a test which runs a sub-shell directly (here I'm executing from another directory to make sure expansion doesn't happen prematurely):

~/test$ cd ..  ~$ bash -c "cd test ; echo *"  file1 file2 file3  ~$ bash -c "cd test ; echo !(file2)"  # expected output: file1 file3  bash: -c: line 0: syntax error near unexpected token `('  bash: -c: line 0: `cd test ; echo !(file2)'  

I've tried all kinds of escaping, but nothing I've come up with has worked correctly. I also suspected extglob is not set in a sub-shell, but that's not the case:

~$ bash -c "shopt -s extglob ; cd test ; echo !(file2)"  bash: -c: line 0: syntax error near unexpected token `('  bash: -c: line 0: `cd test ; echo !(file2)'  

Any solution appreciated!


  $ bash -O extglob -c 'echo !(file2)'  file1 file3  


bash parses each line before executing it, so "shopt -s extglob" won't have taken effect when bash is validating the globbing pattern syntax. The option can't be enabled on the same line. That's why the "bash -O extglob -c 'xyz'" solution (from Randy Proctor) works and is required.


Here's another way, if you want to avoid eval and you need to be able to turn extglob on and off within the subshell. Just put your pattern in a variable:

bash -c 'shopt -s extglob; cd test; patt="!(file2)"; echo $patt; shopt -u extglob; echo $patt'  

gives this output:

file1 file3  !(file2)  

demonstrating that extglob was set and unset. If the first echo had quotes around the $patt, it would just spit out the pattern like the second echo (which probably should have quotes).


Well, I don't have any real experince with extglob, but I can get it to work by wrapping the echo in an eval:

$ bash -c 'shopt -s extglob ; cd  test ; eval "echo !(file2)"'  file1 file3  

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