quotes - Escape backquote in a double-quoted string in shell

Question

For the command: /usr/bin/sh -c "ls 1`" (a backquote after 1).

How to make it run successfully? Adding a backslash before "`" does not work. ` is a special char as we know, and I tried surrounding it with single quote too (/usr/bin/sh -c "ls 1'`'"), but that doesn't work either.

The error always are:

% /usr/bin/sh -c "ls 1`"
Unmatched `

Answer 1

You need to escape the backtick, but also escape the backslash:

$ touch 1`
$ /bin/sh -c "ls 1\`"
1`

The reason you have to escape it "twice" is because you're entering this command in an environment (such as a shell script) that interprets the double-quoted string once. It then gets interpreted again by the subshell.

You could also avoid the double-quotes, and thus avoid the first interpretation:

$ /bin/sh -c 'ls 1`'
1`

Another way is to store the filename in a variable, and use that value:

$ export F='1`'
$ printenv F
1`
$ /bin/sh -c 'ls $F'  # note that /bin/sh interprets $F, not my current shell
1`

And finally, what you tried will work on some shells (I'm using bash, as for the above examples), just apparently not with your shell:

$ /bin/sh -c "ls 1'`'"
1`
$ csh  # enter csh, the next line is executed in that environment
% /bin/sh -c "ls 1'`'"
Unmatched `.

I strongly suggest you avoid such filenames in the first place.