makefile-usage.sh

#!/bin/bash

# --------------------------------------------------
# Generate help messages from Makefile
# --------------------------------------------------
#
# Example Makefile
#
# ```
# ## This is no displayed, this is just a comment
#
# ## This will be displayed as a help message
# ## And this too
# help:
#   @makefile-usage.sh $(MAKEFILE_LIST)
# ```
#
# And the help message is...
#
# ```
# $ make help
# Usage:
#   make [target]
#
# Targets:
#   help                  This will be displayed as a help message
#                         And this too
# ```

makefile=$1
target_max_char=$2

if [ -z "$target_max_char" ]; then
    target_max_char=20
fi

white_spaces=$(printf '%'$target_max_char's')

echo 'Usage:'
echo '  make [target]'
echo ''
echo 'Targets:'
awk '
{ \
    if ($0 ~ /^#!/) { \
        # Collect help messages \
        if (helpMessage) { \
            helpMessage = helpMessage "\n'"$white_spaces"' "; \
        } \
        helpMessage = helpMessage substr($0, 3); \
    } else if ($0 ~ /^[a-zA-Z\-_0-9]+:/) { \
        # Display a help message when we find a task \
        colonPos = index($0, ":") - 1; \
        target = substr($0, 0, colonPos); \
        if (helpMessage) { \
            printf "  %-'"$target_max_char"'s %s\n", target, helpMessage; \
            helpMessage = ""; \
        } \
    } else { \
        # Empty the help message \
        helpMessage = ""; \
    } \
}' $makefile