uri-relate

#!/bin/bash
set -euf -o pipefail
out () { printf %s\\n "$*" ; }

##
# Combine a base URI and relative URI to produce an absolute URI.
#
# Examples:
#
#     $ uri-relate "http://example.com/a/b/c/" "index.html"
#     http://example.com/a/b/c/index.html"
#
#     $ uri-relate "http://example.com/a/b/c/" "/index.html"
#     http://example.com/index.html"
#
#     $ uri-relate "http://example.com/a/b/c/" "//my.com/index.html"
#     http://my.com/index.html"
#
# Important: this script merely handles a few of the common cases,
# sufficient for our immediate needs for our current projects.
#
# TODO: add more syntax possiblities; implement URI standards.
#
##

base="$1"
rel="$2"
abs=""
if [[ "$rel" =~ :// ]]; then
    abs="$rel"
elif [[ "$rel" =~ ^// ]]; then
    abs=$(out "$base" | uri-scheme name)":$rel"
elif [[ "$rel" =~ ^/ ]]; then
    read name authority < <(out "$base" | uri-scheme name authority)
    abs="$name://$authority$rel"
else
    abs="$base/$rel"
fi
out "$abs"