Mailing List Archive: sed command via SSH not working as expected

Hi,

I am using openssh from Debian Lenny which is version 1:5.1p1-5.

I am using ssh to run a command on a remote host running Debian Lenny as
well.

The line I am editing with sed looks like this:
'(proxyAddresses=*)' 2>$ERRORLOG | $GREP -if $RELAYDOMAINS | $GREP -Fi
smtp \

I am running the following command to update the line as follows:
ssh root@remote.example.com "sed -i 's/$GREP -Fi smtp/$GREP -Fi smtp |
$SORT -u/' /usr/local/bin/script.sh"

But what I find is that the line ends up looking like this on the remote
host:
'(proxyAddresses=*)' 2>$ERRORLOG | $GREP -if $RELAYDOMAINS | $GREP -Fi
smtp | -u \

The important part being "| -u" which should look like "| $SORT -u".

This command works fine when running it on the command line directly.

Could I be missing something or perhaps this is a bug?

Thanks,

James

On Fri, 2009-08-21 at 15:50 +1000, James Robertson wrote:
> I am running the following command to update the line as follows:
> ssh root@remote.example.com "sed -i 's/$GREP -Fi smtp/$GREP -Fi smtp |
> $SORT -u/' /usr/local/bin/script.sh"

Hypothesis: Your variables are all expanded to empty strings.

You use single quotes to protect the command you give sed but these
single quotes are meaningless *on the local side* because you put them
inside double quotes. (In other word, the single quotes inside the
double quotes have no special shell meaning on the local side.) When
you issue the command, your local shell interprets it as:

arg 0 = ssh
arg 1 = root@remote.example.com
arg 2 = sed -i 's/ -Fi smtp/ -Fi smtp | -u/' /usr/local/bin/script.sh

arg 2 is what the shell on the remote side executes. You still get a
substitution because as it so happens if $GREP is removed you still get
a match!

Execute the following and you'll see what happens to your variables:

$ ssh root@remote.example.com "echo 's/$GREP -Fi smtp/$GREP -Fi smtp | $SORT -u/'"

> This command works fine when running it on the command line directly.

Presumably this is what you run:

$ sed -i 's/$GREP -Fi smtp/$GREP -Fi smtp | $SORT -u/' /usr/local/bin/script.sh

That's not a problem because there are no double quotes to mess up the
protection which single quotes provide.

Notice the difference of output between this:

$ echo 's/$GREP -Fi smtp/$GREP -Fi smtp | $SORT -u/'

and this:

$ bash -c "echo 's/$GREP -Fi smtp/$GREP -Fi smtp | $SORT -u/'"

> Could I be missing something or perhaps this is a bug?

No bug.

Switch the quotes form single to double and vice-versa and use backslash
in the double quotes to prevent variable expansion. Example:

$ bash -c 'echo "s/\$GREP -Fi smtp/\$GREP -Fi smtp | \$SORT -u/"'

Good luck,
Louis