How do I escape a "$" in bitbake/yocto?

Question

One of my recipes in Yocto need to create a file containing a very specific line, something like:

${libdir}/something

To do this, I have the recipe task:

do_install() {
    echo '${libdir}/something' >/path/to/my/file
}

Keeping in mind that I want that string exactly as shown, I can't figure out how to escape it to prevent bitbake from substituting in its own value of libdir.

I originally thought the echo command with single quotes would do the trick (as it does in the bash shell) but bitbake must be interpreting the line before passing it to the shell. I've also tried escaping it both with $$ and \$ to no avail.

I can find nothing in the bitbake doco about preventing variable expansion, just stuff to do with immediate, deferred and Python expansions.

What do I need to do to get that string into the file as is?

Answer 1

Bitbake seems to have particular issues in preventing expansion from taking place. Regardless of whether you use single or double quotes, it appears that the variables will be expanded before being passed to the shell.

Hence, if you want them to not be expanded, you need to effectively hide them from BitBake, and this can be done with something like:

echo -e '\x24{libdir}/something' >/path/to/my/file

This uses the hexadecimal version of $ so that BitBake does not recognise it as a variable to be expanded.

You do need to ensure you're running the correct echo command however. Under some distros (like Ubuntu), it might run the sh-internal echo which does not recognise the -e option. In order to get around that, you may have to run the variant of echo that lives on the file system (and that does recognise that option):

/bin/echo -e '\x24{libdir}/something' >/path/to/my/file