escaping double-quotes inside the script?

GKnight · #1 (**permalink**) 05-05-2008

I'm having a strange problem with escaping double-quotes. I have a script that looks like this:

Code:

#!/bin/bash

[snip]

for HOST in `cat $INFILE | grep -v ^#`
do

        for VFILER in `some_command`
        do
                echo " "
                echo -e '\E[32;40m' "  **************** VFiler $VFILER on $HOST ***************"; tput sgr0
                ssh $HOST "vfiler run $VFILER "$COMMAND""
                echo " "
                echo " "
        done
done

The problem with ssh command is that it needs to enclose the actual command in double quotes, i.e. this will execute correctly:

Code:

ssh nas01a "vfiler run fs03n cifs shares -change * -novscanread"

but this will return an error:

Code:

ssh nas01a vfiler run fs03n cifs shares -change * -novscanread

In other words, I need to enclose the contents of the ssh command in double-quotes. How can I do it in the script? The way it is above, the quotes are not passed to the ssh command. This doesn't work:

Code:

ssh $HOST \""vfiler run $VFILER "$COMMAND""\"

What am I doing wrong?

Klashxx · #2 (**permalink**) 05-05-2008

Try:

Code:

eval ssh $HOST \\\"vfiler run $VFILER "$COMMAND"\\\"

GKnight · #3 (**permalink**) 05-05-2008

Quote:

Originally Posted by Klashxx

Try:

Code:

eval ssh $HOST \\\"vfiler run $VFILER "$COMMAND"\\\"

Thanks! eval definitely helped, this works:

Code:

eval ssh $HOST \"vfiler run $VFILER "$COMMAND"\"

@ bakunin

I tried escaping backslashes inside double quotes as you suggested - still no go. Thankfully eval does the trick!

bakunin · #4 (**permalink**) 05-05-2008

Quote:

Originally Posted by GKnight

This doesn't work:

Code:

ssh $HOST \""vfiler run $VFILER "$COMMAND""\"

What am I doing wrong?

You do it exactly the wrong way round: you have to escape the inner quotes toprotect them from being interpreted by the shell the first time.

Here is what happens to your command:

1. The shell interprets it, thus removing the unescaped quotes from the string and applying them on the string. In the same step the variables are expanded (textually replaced by their value).

2. The interpreted string is then split up into the command intself (ssh) and its options and/or parameters ($HOST ...)

3. Only now ssh itself starts its work - it opens up a connection to the remote host and feeds it what it was given as command line.

4. The shell on the remote host executes *its* command line, more or less starting over from 1.

What do we learn from that? We want to preserve the quotes from being interpreted by the first shell, so we have to make them look like ordinary characters withot special meaning to it - this is what "escaping" means.

Hence we have to put the double quotes *inside* the string, not outside:

Code:

ssh $HOST "\"some command\""

This will be cooked by the first shell to (in the following, "<>" is only delimiting the parts of the command)

Code:

<ssh> <hostname> <"some command">

The escaped double quotes will now be literal quotes so the second shell will interpret them.

I hope this helps.

bakunin

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