Dash -x fails with Bad substitution error

Question

I'm trying to learn how to write portable shell scripts, to do so I'm starting to migrating my personal utilities from bash to sh (dash on my system). There is however a error I'm getting in all cases when I try to run the scripts in debugging mode $ dash -x script

For instance, on this script:

#!/bin/sh
echo hi

If I run it as: $ dash script, I get the 'hi' string, however if I run it as: $ dash -x script or if I add the set -x command before echo:

#!/bin/sh
set -x
echo hi

It fails with the error:

script.sh: 3: script.sh: Bad substitution

this makes very difficult to debug my scripts. I'm running ubuntu 12.04 with dash 0.5.7-2ubuntu2

Answer 1

Just by the time I finished writing my question I realized I was using a personalized PS4 (which is used in xtrace mode), my PS4 was defined as:

>>(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }

I changed temporarily as PS4=">>" and everything went ok, I can now debug my scripts on dash. Hope this helps someone.