Question

if I have

if [ ! -e $dir ];
then
 mkdir $dir
fi 

work, but not

[[ ! -e $dir ]] || mkdir $dir 

why ?

Edit 0

with [[ ... I get

 line 34: [[ !: command not found

Edit 1

bash --version
GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

Edit 2

in some case work and some case don’t work, two consecutives commands

[user@host ~]$ [ -e /tmp ] && date
-bash: [: missing `]'
[user@host ~]$ [ -e /tmp ] && date
mar jun 26 10:05:50 CLT 2012

Answer 1

Especially after edit 2, this really looks to me like a problem with “funny” characters, either nonprinting characters getting mixed in, or normal-looking-but-weird characters like nonbreaking spaces. These can be fairly hard to detect; things can look completely normal in an editor, and even if you view a script with something like cat -v it won’t always show funny characters clearly. If you have xxd on your system, it’s a really good way to see precisely what’s in the file. Here’s a quick demo of this type of problem:

$ cat -v nbsptest 
#!/bin/bash -x
[ -e /tmp ] && date
[ -e /tmp ] && date
[ -e /tmp ] && date
$ ./nbsptest 
+ '[ -e' /tmp ']'
./nbsptest: line 2: [ -e: command not found
+ '[' -e '/tmp ]'
./nbsptest: line 3: [: missing `]'
+ '[' -e /tmp ']'
+ date
Sat Jun 30 10:53:56 PDT 2012
$ xxd nbsptest 
0000000: 2321 2f62 696e 2f62 6173 6820 2d78 0a5b  #!/bin/bash -x.[
0000010: c2a0 2d65 202f 746d 7020 5d20 2626 2064  ..-e /tmp ] && d
0000020: 6174 650a 5b20 2d65 202f 746d 70c2 a05d  ate.[ -e /tmp..]
0000030: 2026 2620 6461 7465 0a5b 202d 6520 2f74   && date.[ -e /t
0000040: 6d70 205d 2026 2620 6461 7465 0a         mp ] && date.

The script looks completely normal with cat -v (and more, vi, etc), but the first two commands fail. xxd shows why: the first command has a UTF-8 nonbreaking space between the [ and the -e (this shows as c2a0 in the hex listing, [..-e in the text listing) and the second command has a nonbreaking space between /tmp and ] (/tmp..] in the text listing).

The -x display (I used bash -x to invoke it, you can also use set -x as @CodeGnome suggested) also gives a hint about what’s going on. For the first command, it listed it as '[ -e' /tmp ']' — note the quotes around [ -e, which indicates that the shell is treating that all as one “word”, which means it doesn’t think that’s a space in the middle of it. Similarly, the second command is displayed as '[' -e '/tmp ]' with the quotes indicating that it thinks /tmp ] is all one “word”.