bash for strange expansion

doru · 12-17-2014, 03:14 PM

Code:

touch a b a\(c\)b
$ ls *\(c\)*
a(c)b
$ for a in *\(c\)*; do ls $a; done
a(c)b
# this is ok 
rm a\(c\)b
$ ls *\(c\)*
ls: cannot access *(c)*: No such file or directory
$ for a in *\(c\)*; do ls $a; done
a  b
# this is not clear. please tell me why would this happen?!

smallpond · 12-17-2014, 03:37 PM

Does this give you the behavior you expect?

Code:

shopt -s nullglob

doru · 12-17-2014, 04:28 PM

Quote:

Originally Posted by smallpond

Does this give you the behavior you expect?

Code:

shopt -s nullglob

Yes it does, thank you for your answer.
Why would be ls inconsistent with for, and why would *\(c\)* expand to the list of files as one word? I should be able to understand it by myself starting from here.

jpollard · 12-17-2014, 04:35 PM

Looks like you deleted the file.

suicidaleggroll · 12-17-2014, 04:40 PM

Put quotes around your variable in the for loop, same as you would if there's a space or any other "bad" character.

Code:

$ touch a b
for a in *\(c\)*; do ls $a; done
a  b
$ for a in *\(c\)*; do ls "$a"; done
ls: cannot access *(c)*: No such file or directory

same as this

Code:

$ touch "a b"
$ ls *\ *
a b
$ for a in *\ *; do ls $a; done
ls: cannot access a: No such file or directory
ls: cannot access b: No such file or directory
$ for a in *\ *; do ls "$a"; done
a b

If there's ever a chance you're going to have a character that requires delimiting (-, (, space, etc.) stored inside a variable, then you need to stick quotes around it when you use it.

doru · 12-18-2014, 02:34 PM

Sorry to bother you again, but please tell me why does this happen. () should introduce some subshell which here should result in an error.

Code:

$ ls *()*
a  a(c)b  a(c)c  b
$ ls *()
ls: cannot access *(): No such file or directory
$ ls ()*
bash: syntax error near unexpected token `('
$

doru · 12-18-2014, 02:48 PM

Quote:

Originally Posted by doru

Sorry to bother you again, but please tell me why does this happen. () should introduce some subshell which here should result in an error.

Code:

$ ls *()*
a  a(c)b  a(c)c  b
$ ls *()
ls: cannot access *(): No such file or directory
$ ls ()*
bash: syntax error near unexpected token `('
$

OK, so *() is some pattern matching in pathname expansion. So bash is looking for some file with a void name? OK, so nothing matches nothing, that's right. I did fall into a succession of traps here, did I not? Thank you all,