Parse URL in shell script

This solution in principle works the same as Adam Ryczkowski's, in this thread - but has improved regular expression based on RFC3986, (with some changes) and fixes some errors (e.g. userinfo can contain '_' character). This can also understand relative URIs (e.g. to extract query or fragment).

# !/bin/bash

# Following regex is based on https://www.rfc-editor.org/rfc/rfc3986#appendix-B with
# additional sub-expressions to split authority into userinfo, host and port
#
readonly URI_REGEX='^(([^:/?#]+):)?(//((([^:/?#]+)@)?([^:/?#]+)(:([0-9]+))?))?(/([^?#]*))(\?([^#]*))?(#(.*))?'
#                    ↑↑            ↑  ↑↑↑            ↑         ↑ ↑            ↑ ↑        ↑  ↑        ↑ ↑
#                    |2 scheme     |  ||6 userinfo   7 host    | 9 port       | 11 rpath |  13 query | 15 fragment
#                    1 scheme:     |  |5 userinfo@             8 :…           10 path    12 ?…       14 #…
#                                  |  4 authority
#                                  3 //…

parse_scheme () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[2]}"
}

parse_authority () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[4]}"
}

parse_user () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[6]}"
}

parse_host () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[7]}"
}

parse_port () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[9]}"
}

parse_path () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[10]}"
}

parse_rpath () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[11]}"
}

parse_query () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[13]}"
}

parse_fragment () {
    [[ "$@" =~ $URI_REGEX ]] && echo "${BASH_REMATCH[15]}"
}

The above, refined (added password and port parsing), and working in /bin/sh:

# extract the protocol
proto="`echo $DATABASE_URL | grep '://' | sed -e's,^\(.*://\).*,\1,g'`"
# remove the protocol
url=`echo $DATABASE_URL | sed -e s,$proto,,g`

# extract the user and password (if any)
userpass="`echo $url | grep @ | cut -d@ -f1`"
pass=`echo $userpass | grep : | cut -d: -f2`
if [ -n "$pass" ]; then
    user=`echo $userpass | grep : | cut -d: -f1`
else
    user=$userpass
fi

# extract the host -- updated
hostport=`echo $url | sed -e s,$userpass@,,g | cut -d/ -f1`
port=`echo $hostport | grep : | cut -d: -f2`
if [ -n "$port" ]; then
    host=`echo $hostport | grep : | cut -d: -f1`
else
    host=$hostport
fi

# extract the path (if any)
path="`echo $url | grep / | cut -d/ -f2-`"

Posted b/c I needed it, so I wrote it (based on @Shirkin's answer, obviously), and I figured someone else might appreciate it.

[EDIT 2019] This answer is not meant to be a catch-all, works for everything solution it was intended to provide a simple alternative to the python based version and it ended up having more features than the original.

---

It answered the basic question in a bash-only way and then was modified multiple times by myself to include a hand full of demands by commenters. I think at this point however adding even more complexity would make it unmaintainable. I know not all things are straight forward (checking for a valid port for example requires comparing hostport and host) but I would rather not add even more complexity.

---

[Original answer]

Assuming your URL is passed as first parameter to the script:

#!/bin/bash

# extract the protocol
proto="$(echo $1 | grep :// | sed -e's,^\(.*://\).*,\1,g')"
# remove the protocol
url="$(echo ${1/$proto/})"
# extract the user (if any)
user="$(echo $url | grep @ | cut -d@ -f1)"
# extract the host and port
hostport="$(echo ${url/$user@/} | cut -d/ -f1)"
# by request host without port    
host="$(echo $hostport | sed -e 's,:.*,,g')"
# by request - try to extract the port
port="$(echo $hostport | sed -e 's,^.*:,:,g' -e 's,.*:\([0-9]*\).*,\1,g' -e 's,[^0-9],,g')"
# extract the path (if any)
path="$(echo $url | grep / | cut -d/ -f2-)"

echo "url: $url"
echo "  proto: $proto"
echo "  user: $user"
echo "  host: $host"
echo "  port: $port"
echo "  path: $path"

I must admit this is not the cleanest solution but it doesn't rely on another scripting language like perl or python. (Providing a solution using one of them would produce cleaner results ;) )

Using your example the results are:

url: [email protected]/some/random/path
  proto: sftp://
  user: user
  host: host.net
  port:
  path: some/random/path

This will also work for URLs without a protocol/username or path. In this case the respective variable will contain an empty string.

[EDIT]
If your bash version won't cope with the substitutions (${1/$proto/}) try this:

#!/bin/bash

# extract the protocol
proto="$(echo $1 | grep :// | sed -e's,^\(.*://\).*,\1,g')"

# remove the protocol -- updated
url=$(echo $1 | sed -e s,$proto,,g)

# extract the user (if any)
user="$(echo $url | grep @ | cut -d@ -f1)"

# extract the host and port -- updated
hostport=$(echo $url | sed -e s,$user@,,g | cut -d/ -f1)

# by request host without port
host="$(echo $hostport | sed -e 's,:.*,,g')"
# by request - try to extract the port
port="$(echo $hostport | sed -e 's,^.*:,:,g' -e 's,.*:\([0-9]*\).*,\1,g' -e 's,[^0-9],,g')"

# extract the path (if any)
path="$(echo $url | grep / | cut -d/ -f2-)"