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Bash : Why are spaces important here ?


 
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# 8  
Quote:
Originally Posted by John K
So, [ character being misinterpreted as a command
That's the thing -- it's not being misinterpreted, it is a command.

Code:
$ whereis [

[: /usr/bin/[

$ ls -l /usr/bin/[

-rwxr-xr-x 1 root root 39424 Jun  5  2014 /usr/bin/[

$

It's usually a built-in as well, but the command must exist. The shell must treat it as a command.

( ) are not commands.
This User Gave Thanks to Corona688 For This Post:
# 9  
Quote:
Originally Posted by Corona688
Code:
$ whereis [

[: /usr/bin/[
$

It's usually a built-in as well, but the command must exist. The shell must treat it as a command.

Rather than whereis, use type; It tells you what the shell will actually use:

Code:
$ type [
[ is a shell builtin

With the -a option, it gives all the possible commands that could be executed:

Code:
$ type -a [
[ is a shell builtin
[ is /usr/bin/[

[ is also a synonym for test.
These 4 Users Gave Thanks to cfajohnson For This Post:
# 10  
For beginners, just to be VERY aware '[' and 'test' are NOT quite the same although they do a similar thing...
They cannot __cross-pollnate__.
Code:
Last login: Tue Jan 20 18:45:37 on ttys000
AMIGA:barrywalker~> var="Bazza..."
AMIGA:barrywalker~> if test "$var" == "Bazza..."; then echo "$var"; fi
Bazza...
AMIGA:barrywalker~> if [ "$var" == "Bazza..."; then echo "$var"; fi
-bash: [: missing `]'
AMIGA:barrywalker~> # Oh dear '[' and 'test' are not quite the same...
AMIGA:barrywalker~> if [ "$var" == "Bazza..." ]; then echo "$var"; fi
Bazza...
AMIGA:barrywalker~> if test "$var" == "Bazza..." ]; then echo "$var"; fi
-bash: test: too many arguments
AMIGA:barrywalker~> # Oh dear 'test' doesn't allow a closing square bracket...
AMIGA:barrywalker~> _

This User Gave Thanks to wisecracker For This Post:
# 11  
Quote:
Originally Posted by wisecracker
For beginners, just to be VERY aware '[' and 'test' are NOT quite the same although they do a similar thing...

The only difference is that [ requires a closing ].
Code:
AMIGA:barrywalker~> if test "$var" == "Bazza..."; then echo "$var"; fi

Also note that test/[ uses = not == (though bash and ksh accept it).

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