Single-quotes in variables

[xyz000]

Hello,

I'm relatively new to Linux so forgive me if the answer to this question is simple.

I'm attempting to use a script to invoke VLC from the command line. Some of the VLC parameters are enclosed in single quotes and some of the parameters are enclosed in double-quotes. The command typically looks like this:

cvlc "source" --sout '#duplicate'

I can make this work in simple script as follows:

#!/bin/bash
cvlc "source" --sout '#duplicate'

What I would like to do is to assign the entire command to a variable. I tried the following by escaping the double-quotes:

#!/bin/bash
CMD="cvlc \"source\" --sout '#duplicate'"
echo Command is: $CMD
$CMD

This gives the following output:

Command is: cvlc "source" --sout '#duplicate'

...so I believe the $CMD variable is correctly formatted. Yet VLC rejects the parameters when I use the CMD variable. I'm sure this is something to do with the way bash handles single-quotes and double-quotes rather than any kind of error in VLC.

Can anyone see what I might have done wrong or suggest a correction?

Thanks!

[lomcevak]

Not sure but try this to execute the command:

eval $CMD

[xyz000]

Thanks for the suggestion. I've found a solution that works for me now. From experimentation it seems that single quotes and double quotes are often (always?) interchangable so, by changing the single quotes to double quotes, I can make my script behave correctly.

I found the following text in an a dusty textbook:

The characters below can be used for quoting:

" " Everything between " and " is taken literally, except for the following characters that keep their special meaning:

$ Variable substitution will occur.

`Command substitution will occur

" This marks the end of the double quote.

' ' Everything between ' and ' is taken literally except for another '.
\ The character following \ is taken literally. Use within "" to escape ", $ and `. Often used to escape itself, spaces and newlines.

I also found that adding "-x" to #!/bin/bash is helpful for tracing script execution:

#!/bin/bash -x

I hope these tips help others some day.