Linux 愛好者園地

Q. How can I Debug a shell scripts? A. This is most common question asked by new admins or UNIX user. Shell scripting debugging can be boring job (read as not easy). There are various ways to debug a shell script. Method # 1: Use -x option Run a shell script with -x option. $ bash -x script-name $ bash -x domains.sh Method # 2: Use of set builtin command Bash 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: #!/bin/bash clear # turn on debug mode set -x for f in * do file $f done # turn OFF debug mode set +x ls # more commands You can replace standard #!/bin/bash with (for debugging) #!/bin/bash -xv Method # 3: Use of intelligent DEBUG function Add special variable _DEBUG. Set to `on’ when you need to debug a script: _DEBUG="on" Put the following function at the beginning of the script: function DEBUG() { [ "$_DEBUG" == "on" ] && $@ || : } Now wherever you need debugging simply use DEBUG function DEBUG echo "File is $filename" OR DEBUG set -x Cmd1 Cmd2 DEBUG set +x When debugging done and before moving a script to production set _DEBUG to off No need to delete debug lines. _DEBUG="off" # set to anything but not to 'on' Sample script: #!/bin/bash _DEBUG="on" function DEBUG() { [ "$_DEBUG" == "on" ] && $@ || : } DEBUG echo 'Reading files' for i in * do grep 'something' $i > /dev/null [ $? -eq 0 ] && echo "Found in $i file" || : done DEBUG set -x a=2 b=3 c=$(( $a + $b )) DEBUG set +x echo "$a + $b = $c" Save and run the script: $ ./script.sh Output: Reading files Found in xyz.txt file + a=2 + b=3 + c=5 + DEBUG set +x + '[' on == on ']' + set +x 2 + 3 = 5 Now set DEBUG to off _DEBUG="off" Run script: $ ./script.sh Output: Found in xyz.txt file 2 + 3 = 5 Above is a simple but quite effective technique. You can also try to use DEBUG as an alias instead of function.