Bash: how do I pass a double quoted string to a command?

Nylex · 04-17-2007, 01:58 PM

I'm trying to write a shell script to rip CDs using cdda2wav. I have the track names in a file and I'm reading these in and then creating a string like so:

Code:

#!/bin/bash

# Save stdin
exec 6<&0

# stdin is now tracks
exec < tracks

count=0
command1="cdda2wav -s -t"

while read line
do
  let "count += 1"
  command2="$command1 $count -x dev=/dev/cdrw \""$line\"
  $command2
done

exec 0<&6 6<&-

If I echo command2, I get what I expect, e.g.

cdda2wav -s -t 1 -x dev=/dev/cdrw "Ghost Is Back".

This is what I'd usually use on the command line. The problem, however is that when the command is executed in my script, the file name output for the above cdda2wav example ends up being "Ghost.wav, i.e. there's a " at the beginning and the title isn't complete.

What am I doing wrong?

Thanks!

osor · 04-17-2007, 02:21 PM

Change

Code:

  command2="$command1 $count -x dev=/dev/cdrw \""$line\"

to

Code:

  command2="$command1 $count -x dev=/dev/cdrw \"$line\""

Nylex · 04-17-2007, 02:26 PM

That hasn't made a difference.

druuna · 04-17-2007, 03:10 PM

Hi,

Sorry, came up with the same as the prvious replyer.......

Nylex · 04-17-2007, 03:12 PM

OK, there's something wrong with me. I can't see the difference between your line, druuna and osor's line (other than the colours!).

osor · 04-17-2007, 08:15 PM

The red double-quote is the one to move…

ntubski · 04-17-2007, 11:16 PM

Instead of using echo, use a program that outputs its command line arguments:

Code:

['~/bin/args.py', 'cdda2wav', '-s', '-t', '1', '-x', 'dev=/dev/cdrw', '"Ghost', 'Is', 'Back"']

So you can see the double quotes are in the right place but weren't interpreted by bash. You need to use eval $command2, eval will cause bash to interpret things properly.

Nylex · 04-18-2007, 01:17 AM

Quote:

Originally Posted by osor

The red double-quote is the one to move…

I said that didn't help (well, by itself). It was using "eval $command2" instead of just "$command2" that worked.

Quote:

Originally Posted by ntubski

Instead of using echo, use a program that outputs its command line arguments:

Code:

['~/bin/args.py', 'cdda2wav', '-s', '-t', '1', '-x', 'dev=/dev/cdrw', '"Ghost', 'Is', 'Back"']

So you can see the double quotes are in the right place but weren't interpreted by bash. You need to use eval $command2, eval will cause bash to interpret things properly.

I'm not sure what the first part of your answer means, but using "eval $command2" works. Thanks!

Quick question: I don't really need to save stdin and restore it at the end, do I?

ntubski · 04-18-2007, 09:36 AM

Quote:

Originally Posted by Nylex

I'm not sure what the first part of your answer means, but using "eval $command2" works. Thanks!

echo can only show you what the command line looks like as a string:

Code:

~% echo foo bar                                                                
foo bar
~% echo 'foo bar'                                                              
foo bar
~% args.py foo bar                                                             
['~/bin/args.py', 'foo', 'bar']
~% args.py 'foo bar'                                                           
['~/bin/args.py', 'foo bar']

Quote:

Quick question: I don't really need to save stdin and restore it at the end, do I?

how about

Code:

#!/bin/bash
count=0
command1="cdda2wav -s -t"

while read line
do
  let "count += 1"
  command2="$command1 $count -x dev=/dev/cdrw \""$line\"
  eval $command2
done <tracks