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Old 06-01-2012, 04:53 AM   #1
psrdotcom
LQ Newbie
 
Registered: Sep 2011
Posts: 5

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Shellscript variable as command string


Hi Friends,

When I was trying form a command from different variables to one variable, I was successive.

Sample:

CMD="mount"

CMD=$CMD" /dev/sdb"

CMD=$CMD" /mnt/disk0/"

echo "The command is: $CMD"

$CMD

Output:
The command is: mount /dev/sdb /mnt/disk0
Error: No such file or directory:
""

Note: Both the /dev/sdb and /mnt/disk0 exists.

If I am running the same command without using variable from the script, it was working fine.

Please help me to get out of this problem.
 
Old 06-01-2012, 05:26 AM   #2
evo2
Guru
 
Registered: Jan 2009
Location: Japan
Distribution: Debian, SL
Posts: 5,315

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Hi,

seems to be a quoting issue. Can you try the following
Code:
CMD="mount"
CMD="$CMD /dev/sdb"
CMD="$CMD /mnt/disk0/"
echo "The command is: $CMD"
$CMD
Evo2.
 
Old 06-01-2012, 07:41 AM   #3
David the H.
Bash Guru
 
Registered: Jun 2004
Location: Osaka, Japan
Distribution: Debian sid + kde 3.5 & 4.4
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The simple answer here is that you don't do it that way. Variables are for storing data, not code.

I'm trying to put a command in a variable, but the complex cases always fail!
http://mywiki.wooledge.org/BashFAQ/050


Once a string is stored in a variable, the parsing rules for it are very different, and you just can't reliably run a complex command that way. If you want to set up a dynamic command of some kind, use a function.


Code:
CMD() {

	echo "The command is: mount $@"
	mount "$@"

}

CMD /dev/sdb /mnt/disk0

Last edited by David the H.; 06-01-2012 at 07:45 AM. Reason: added code
 
1 members found this post helpful.
Old 06-01-2012, 03:34 PM   #4
psrdotcom
LQ Newbie
 
Registered: Sep 2011
Posts: 5

Original Poster
Rep: Reputation: Disabled
Solved

I have wrote the command to a file and executed the file within the script.


Quote:
Originally Posted by David the H. View Post
The simple answer here is that you don't do it that way. Variables are for storing data, not code.

I'm trying to put a command in a variable, but the complex cases always fail!
http://mywiki.wooledge.org/BashFAQ/050


Once a string is stored in a variable, the parsing rules for it are very different, and you just can't reliably run a complex command that way. If you want to set up a dynamic command of some kind, use a function.


Code:
CMD() {

	echo "The command is: mount $@"
	mount "$@"

}

CMD /dev/sdb /mnt/disk0
 
  


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