[Help-bash] Why `` in PS4='``' is reduced to empty string?

[Peng Yu]

Hi,

It seems that PS4 is interpreted. But this seems not documented.

Also, is it better to perserve PS4 literally without any inpretation?

$ cat main.sh
#!/usr/bin/env bash
# vim: set noexpandtab tabstop=2:

PS4='*' ./run.sh
PS4=\` ./run.sh
PS4='``' ./run.sh

$ cat run.sh
#!/usr/bin/env bash
# vim: set noexpandtab tabstop=2:

set -x
./script.sh
$ ./main.sh
*./script.sh
`./script.sh
./script.sh

-- 
Regards,
Peng