bash_script_notes.md

Bash Script Example

The following blog post shows a sample bash script covering some inportant aspects in writing a bash script.

Important aspects covered in this script:

• Validate if input arguments are passed
• Parse positional arguments
• Handle parameter values with white space
• Validating the arguments (using regex)
• While loop to iterate through varargs
• Usage of unit functions
• Usage of function that takes inputs and return value
• Using -e option to fail the script on command execution errors
• Using -x option to help debugging the script execution
• Exit the script with success or error status
• Redirect error messages to error console

Executing the script:

Method 1 (in it's own bash shell)

The script can be executed as

bash calculate.sh --operation add --lhs 2 --rhs 3

This is the simplest way to execute the script because:

• The script runs in its own shell
• Doesn't read variables or environment variables from the main shell
• Doesn't leave traces of variables or changes to environment variables after script completion
• Needs only read permission to execute the script

Method 2 (in the main shell where it is invoked)

Another way of executing the script is

Set executable permission for the script

chmod u+x calculate.sh

Execute using relative path

./calculate.sh --operation add --lhs 2 --rhs 3

Or Execute using full path

$HOME/scripts/calculate.sh

The difference from the first style is:

• The script runs in main shell where it is invoked
• Shares variables or environment variables from the main shell
• Leave traces of variables or changes to environment variables after script completion