Debug a script

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You need to run a shell script with -x option from the command line itself:

bash -x script-name

OR

bash -xv script-name

You can also modify shebang line to run an entire script in debugging mode:

#!/bin/bash -x
echo "Hello ${LOGNAME}"
echo "Today is $(date)"
echo "Users currently on the machine, and their processes:"
w

Use of set builtin command

Bash shell offers debugging options which can be turned 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.
• set -n : Read commands but do not execute them. This may be used to check a shell script for syntax errors.

#!/bin/bash
### Turn on debug mode ###
set -x

# Run shell commands
echo "Hello $(LOGNAME)"
echo "Today is $(date)"
echo "Users currently on the machine, and their processes:"

### Turn OFF debug mode ###
set +x

# Add more commands without debug mode

Another example using set -n and set -o noexec:

#!/bin/bash
set -n # only read command but do not execute them
set -o noexec
echo "This is a test"
# no file is created as bash will only read commands but do not executes them 
>/tmp/debug.txt

See also

• Setting shell options

External links

• How to debug a Shell Script under Linux or UNIX.

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