How to debug a Shell Script
Use -x option to debug a shell script
Run a shell script with -x option. This is valid for bash shell scripts as well.
$ ksh -x tesh.sh
$ ksh -v test.sh
Use of set builtin command
korn shell offers debugging options which can be turn on or off using set command.
=> set -x : Display commands and their arguments as they are executed.
=> set -v : Display shell input lines as they are read.
You can use above two command in shell script itself:
<span style="color: rgb(0, 0, 153); font-weight: bold;">#!/bin/ksh</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">clear</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"># turn on debug mode</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">set -x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">for f in *</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">do</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"> file $f</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">done</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"># turn OFF debug mode</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">set +x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">ls</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"># more commands</span>
You can replace standard
#!/bin/ksh
with (for debugging)
#!/bin/ksh -xv
Use of intelligent DEBUG function
Add special variable _DEBUG. Set to `on’ when you need to debug a script:
_DEBUG="on"
Put the following function at the beginning of the script:
function DEBUG()<br />{<br /> [ "$_DEBUG" == "on" ] && $@ || :<br />}
Now wherever you need debugging simply use DEBUG function
DEBUG echo "File is $filename"OR
DEBUG set -xCmd1
Cmd2
DEBUG set +x
When debugging done and before moving a script to production set _DEBUG to off
No need to delete debug lines.
_DEBUG="off" # set to anything but not to 'on'
Sample script:
<span style="color: rgb(0, 0, 153); font-weight: bold;">#!/bin/bash</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">_DEBUG="on"</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">function DEBUG()</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">{</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"> [ "$_DEBUG" == "on" ] && $@ || :</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">}</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">DEBUG echo 'Reading files'</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">for i in *</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">do</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"> grep 'something' $i > /dev/null</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;"> [ $? -eq 0 ] && echo "Found in $i file" || :</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">done</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">DEBUG set -x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">a=2</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">b=3</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">c=$(( $a + $b ))</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">DEBUG set +x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">echo "$a + $b = $c"</span><br />
Save and run the script:
$ ./script.sh
Output:
<span style="color: rgb(0, 0, 153); font-weight: bold;">Reading files</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">Found in xyz.txt file</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ a=2</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ b=3</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ c=5</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ DEBUG set +x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ '[' on == on ']'</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">+ set +x</span><br style="color: rgb(0, 0, 153); font-weight: bold;" /><span style="color: rgb(0, 0, 153); font-weight: bold;">2 + 3 = 5</span><br />
Now set DEBUG to off
_DEBUG="off"
Run script:
$ ./script.sh
Output:
<span style="font-weight: bold; color: rgb(0, 0, 153);">Found in xyz.txt file</span><br style="font-weight: bold; color: rgb(0, 0, 153);" /><span style="font-weight: bold; color: rgb(0, 0, 153);">2 + 3 = 5</span><br />
You can also try to use DEBUG as an alias instead of function.
Links
Korn Shell Debugger by OReilly
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