Parse metadata variables from a markdown file.

extract-meta.sh

#!/usr/bin/env bash
##
## Parse metadata variables from a markdown file.
##
## The key-values are returned as field-deliminated lines to
## stdout, or, as a variable string that can be passed to pandoc
## as command-line parameters.
##
## Delcare metadata in the markdown file using the format:
##   % meta keyname1="value1"
##   %meta keyname2="value2"
##   % meta   keyname3="value3"
##
## As you can see, some of the separating space is optional.

META_REGEX="^%\s*meta\s*"
SEP="="

function print_help {
    echo "Usage: $(basename $0) [options] -f file"
    echo "  -f=file  Markdown file to parse metadata from."
    echo "  -P       Return a variable declaration string for pandoc."
    echo "  -S=sep   Use a different field separator. [=]"
    echo "  -h       Show this usage guide."
}

while getopts "f:PS:h" opt; do
    case $opt in
        f) FILE="$OPTARG";;
        P) OPT_PANDOC=1;;
        S) SEP="$OPTARG";;
        h) print_help; exit 0;;
        \?) print_help; exit 0;;
    esac
done

if [ ! -f "$FILE" ]; then
    print_help
    exit 1
fi

##parse metadata
##
declare -A METADATA

while read line; do
    kv=$(echo "$line" | sed -e "s/$META_REGEX\(\w*\)/\1/g")
    key=$(echo "$kv" | cut -d '=' -f1)
    val=$(echo "$kv" | cut -d '=' -f2)
    METADATA["$key"]="$val"
done < <(cat "$FILE" | grep -P "$META_REGEX")

##print output
##
for key in "${!METADATA[@]}"; do
    if [ -n "$OPT_PANDOC" ]; then
        pandoc_params="$pandoc_params -V $key=${METADATA[$key]}"
    else
        echo "$key$SEP${METADATA[$key]}"
    fi
done

if [ -n "$OPT_PANDOC" ]; then
    echo "$pandoc_params"
fi