Assign string containing null-character () to a variable in Bash

Question

While trying to process a list of file-/foldernames correctly (see my other questions) through the use of a NULL-character as a delimiter I stumbled over a strange behaviour of Bash that I don't understand:

When assigning a string containing one or more NULL-character to a variable, the NULL-characters are lost / ignored / not stored.

For example,

echo -ne "nmk" | od -c   # -> 0000000   n     m     k

But:

VAR1=`echo -ne "nmk"`
echo -ne "$VAR1" | od -c   # -> 0000000   n   m   k

This means that I would need to write that string to a file (for example, in /tmp) and read it back from there if piping directly is not desired or feasible.

When executing these scripts in Z shell (zsh) the strings containing are preserved in both cases, but sadly I can't assume that zsh is present in the systems running my script while Bash should be.

How can strings containing chars be stored or handled efficiently without losing any (meta-) characters?

Answer 1

In Bash, you can't store the NULL-character in a variable.

You may, however, store a plain hex dump of the data (and later reverse this operation again) by using the xxd command.

VAR1=`echo -ne "nmk" | xxd -p | tr -d '
'`
echo -ne "$VAR1" | xxd -r -p | od -c   # -> 0000000    n     m     k