How to debug a bash script? [closed]

Question

Is there any way to debug a bash script? E.g something that prints a sort of execution log like "calling line 1", "calling line 2" etc.

Answer 1

There's good amount of detail on logging for shell scripts via global varaibles of shell. We can emulate the similar kind of logging in shell script: http://www.cubicrace.com/2016/03/log-tracing-mechnism-for-shell-scripts.html

The post has details on introdducing log levels like INFO , DEBUG, ERROR. Tracing details like script entry, script exit, function entry, function exit.

Sample log:

Answer 2

This answer is valid and useful: https://stackoverflow.com/a/951352

But, I find that the "standard" script debugging methods are inefficient, unintuitive, and hard to use. For those used to sophisticated GUI debuggers that put everything at your fingertips and make the job a breeze for easy problems (and possible for hard problems), these solutions aren't very satisfactory.

What I do is use a combination of DDD and bashdb. The former executes the latter, and the latter executes your script. This provides a multi-window UI with the ability to step through code in context and view variables, stack, etc., without the constant mental effort to maintain context in your head or keep re-listing the source.

There is guidance on setting that up here: http://ubuntuforums.org/showthread.php?t=660223

Answer 3

Some trick to debug bash scripts:

Using set -[nvx]

In addition to

set -x

and

set +x

for stopping dump.

I would like to speak about set -v wich dump as smaller as less developped output.

bash <<<$'set -x\nfor i in {0..9};do\n\techo $i\n\tdone\nset +x' 2>&1 >/dev/null|wc -l
21

for arg in x v n nx nv nvx;do echo "- opts: $arg"
    bash 2> >(wc -l|sed s/^/stderr:/) > >(wc -l|sed s/^/stdout:/) <<eof
        set -$arg
        for i in {0..9};do
            echo $i
          done
        set +$arg
        echo Done.
eof
    sleep .02
  done
- opts: x
stdout:11
stderr:21
- opts: v
stdout:11
stderr:4
- opts: n
stdout:0
stderr:0
- opts: nx
stdout:0
stderr:0
- opts: nv
stdout:0
stderr:5
- opts: nvx
stdout:0
stderr:5

Dump variables or tracing on the fly

For testing some variables, I use sometime this:

bash <(sed '18ideclare >&2 -p var1 var2' myscript.sh) args

for adding:

declare >&2 -p var1 var2

at line 18 and running resulting script (with args), without having to edit them.

of course, this could be used for adding set [+-][nvx]:

bash <(sed '18s/$/\ndeclare -p v1 v2 >\&2/;22s/^/set -x\n/;26s/^/set +x\n/' myscript) args

will add declare -p v1 v2 >&2 after line 18, set -x before line 22 and set +x before line 26.

little sample:

bash <(sed '2,3s/$/\ndeclare -p LINENO i v2 >\&2/;5s/^/set -x\n/;7s/^/set +x\n/' <(
        seq -f 'echo $@, $((i=%g))' 1 8)) arg1 arg2
arg1 arg2, 1
arg1 arg2, 2
declare -i LINENO="3"
declare -- i="2"
/dev/fd/63: line 3: declare: v2: not found
arg1 arg2, 3
declare -i LINENO="5"
declare -- i="3"
/dev/fd/63: line 5: declare: v2: not found
arg1 arg2, 4
+ echo arg1 arg2, 5
arg1 arg2, 5
+ echo arg1 arg2, 6
arg1 arg2, 6
+ set +x
arg1 arg2, 7
arg1 arg2, 8

Note: Care about $LINENO will be affected by on-the-fly modifications!

( To see resulting script whithout executing, simply drop bash <( and ) arg1 arg2 )

Step by step, execution time

Have a look at my answer about how to profile bash scripts

Answer 4

I think you can try this Bash debugger: http://bashdb.sourceforge.net/.

Answer 5

You can also write "set -x" within the script.

Answer 6

I built a Bash debugger. Just give it a try. I hope it will help https://sourceforge.net/projects/bashdebugingbash