I have to maintain several shell scripts that perform long sequences of steps like loading data into a database or running a simulation model with pre- and post-processing of the data. There are often failures and scripts has to be rerun starting at some point. With this preprocessor one can define sections of the script that can be selected for execution using command line parameters.

On Mac GNU sed and coreutils required. They should be prefixed with 'g' (e.g., gsed, ghead). Install them as brew install coreutils, do NOT use --with-default-names option.

Insert the directive #phase <name> into your script to split the script into sections. Use test_script.sh as an example. Give some meaningful name for each phase.

Now you can select a phase or several from your script to be executed independently of others. In the following example only the phase load will be executed:

phases load test_script.sh

To execute all phases except for load use the option --skip:

phases --skip load test_script.sh

For more help run phases without arguments.

Phase list contains the names of phases to be executed or skipped. Multiple phases can be specified using comma:

phases load,final test_script.sh

To specify a range of phases use dash (-):

phases load-final test_script.sh

You can mix phases and ranges:

phases load,final-clean test_script.sh

To skip a phase use either --skip option or caret before the phase name in the list. The following command will execute all phases except for load:

phases ^load test_script.sh

Any script starts with an implied phase init that starts at the first line of the script and ends before the first specified phase. This phases is intended for various script initialization tasks like setting variables, defining functions, opening session, checks, etc. This phases will be always executed unless skipped explicitly either with --skip option or with caret (^) in the phase list.

• In skip mode negated phases are simply ignored.
• The order of phases in the list does not matter and the sequence phases will always be preserved as in the original script.

To make sure that all specified phases are properly understood run:

phases -l test_script.sh

Use --output option to save resulting script into a file instead of executing it.

1. Inside your script do not use file paths relative to the script location
2. The names of the phases should not contain punctuation or special characters