UNIX for Dummies Questions & Answers

Hi Gurus,

I am debugging a script. it loops filelist. since the list a very long. when debugging, I only can see the last a few lines. is there any way to stop debuger in the mid of process.

the command I used for debugging is:

Code:

ksh -x scriptName

Thanks in advance

Yes, modify the script...
make it read a key ( any.. you dont care its just for stopping...) you enter...

Add the following to the top of your script and execute it normally. Press the ENTER key to step through the script:

Code:

set -x
trap "read" DEBUG

Not really with invoking it that way. Perhaps you would be better to capture the output to a file and then view that later on:-

Code:

$ ksh -x scriptName >/tmp/script.log 2>&1

If you need to interact with it, you could do the following:-

Code:

$ touch /tmp/script.log
tail -f /tmp/script.log &
ksh -x scriptName >>/tmp/script.log 2>&1

Note the append to log >> in this case.


I hope that this helps.

Robin
Liverpool/Blackburn
UK

This way works perfect

Thanks

You can also select the lines in a script that you want to trace. The command:

Code:

set -x

turns tracing on for following commands in the script, and the command:

Code:

set +x

turns tracing off for following commands.

Don has it - as always - right: instead of tracing the script wholesale you should trace one (small) piece after the other. Set pairs of set -xv and set +xv and move these pairs around while debugging.

Another thing is: debugging output happens on <stderr> and you can catch this output and display it pagewise:

Code:

/your/script_with_tracing.sh 2>&1 | more

My favourite is yet to (mostly) skip tracing altogether. In most cases you can put in some diagnostic messages into your script. Suppose you have the following:

Code:

while [ $value != something ] ; do
     command1
     command2
     value=$(some_command giving some value)
     command3
done

Instead of decorating such a loop with "set +/- xv" you could also build in a diagnostic message and let it run:

Code:

while [ $value != something ] ; do
     command1
     command2

     echo "old value is $value"
     value=$(some_command giving some value)
     echo "new value is $value"
    
     command3
done

Now you will get pairs of before- and after-values and can probably find the culprit. Maybe there is another component involved, so output that too with each pass of the loop. You get the idea.

Once you found and corrected the problem you remove these lines again and start working on the next bug the same way.

Another possibility is to display commands instead of executing them. Replace any:

Code:

problematic_command $value1 $value2

with

Code:

DEBUG="echo "       # somewhere at the beginning of execution

...

$DEBUG problematic_command $value1 $value2

You can decorate several interesting commands like that. If you set DEBUG to "echo" they are not executed but displayed like they would be executed, quite similar to what you see with "set -x". Set DEBUG to "" and they are executed normally again. This way you can switch between debugging runs and normal runs easily.

I hope this helps.

bakunin