9

What are / is the significance of + and ++ at the beginning of bash debug (set -x) output?

The original text looks like this

++ delete 
+ exitstatus=0
+ '[' 0 = 0 ']'
++ delete
+ whiptail --title 'Command output 1311' --separate-output --scrolltext --msgbox '/usr/bin/raspi-config-DEBUG.sh: line 1311: delete: command not found' 17 80 10
+ echo '1317  done printing choice to stdout'
Improve this question

1 Answer 1

Reset to default
17

The + is the PS4 prompt (just like PS1 usually holds $ or some variation thereof, which is the default interactive prompt). It is outputted before each command executed when tracing is enabled with set -x.

The bash manual says this:

PS4

The value of this parameter is expanded as with PS1 and the value is printed before each command bash displays during an execution trace. The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is +.

The multiple + that you may see are due to commands being executed in subshells.

Example showing three levels of subshells:

$ cat script.sh
#!/bin/bash

echo "$( echo "$( echo hi )" )"

$ bash -x script.sh
+++ echo hi
++ echo hi
+ echo hi
hi
Improve this answer
2
  • Great, now for the formatting part - how was it reformatted to look as original text, for future references. Commented Sep 13, 2018 at 15:35
  • 1
    @JanHus You can't reformat it to get the original shell script back. In my example, there is no information that tells me exactly what the original commands looked like. Commented Sep 13, 2018 at 15:39

You must log in to answer this question.