Yes I know realpath exists, but it's not installed by default and sometimes it's easier to tuck a script somewhere convenient...

fullpath.sh

#!/bin/bash
###############################################################################
# fullpath.sh - Find the absolute path to the given file or directory.
# 
# updated: 2017-03-23
# created: 2005-05-25
# author: Kevin C. Krinke <kevin@krinke.ca>
# license: LGPL-2.1
###############################################################################

#
# Global Variables
#

SCRIPT_VERSION=1.0
SCRIPT_NAME=$(basename "$0")

V_NORMAL=1
V_QUIET=0
V_DEBUG=2

G_VERBOSITY=$V_NORMAL
G_NULL_TERMINATE=0
declare -A TARGET_PATHS

#
# Helper Functions
#

function STDOUT () { while [ $# -gt 0 ]; do echo "$1";      shift; done; }
function STDERR () { while [ $# -gt 0 ]; do echo "$1" 1>&2; shift; done; }
function ERROR  () { while [ $# -gt 0 ]; do STDERR "ERROR: $1"; shift; done; }
function DEBUG  () { [ $G_VERBOSITY -ge $V_DEBUG  ] && STDERR "$@"; }
function NOTIFY () { [ $G_VERBOSITY -ge $V_NORMAL ] && STDOUT "$@"; }
function DIE    () { ERROR "$@"; exit 1; }

function display_usage() {
    [ $# -gt 0 ] && ERROR "$@"
    STDERR "usage: ${SCRIPT_NAME} [options] <path>"
    STDERR ""
    STDERR "options:"
    STDERR "  -h --help            this helpful screen"
    STDERR "  -v --verbose         increase verbosity"
    #STDERR "  -q --quiet           silence normal output"
    STDERR "  -z --null            null terminated instead of newlines"
    exit 1
}

export EXPANDED_PATH=
function expand_abspath() {
    this_path=$(echo "$1" | perl -pe "s#^\./#$(pwd)/#;s#^([^/])#${PWD}/\1#;")
    root_path=$(echo "${this_path}" | perl -pe 's/^\///')
    declare -a all_pieces
    typeset -i I
    I=0
    orig_ifs="${IFS}"
    IFS='/'
    for piece in $root_path
    do
        all_pieces[$I]="${piece}"
        I=$((I+1))
    done
    IFS="${orig_ifs}"
    full_path=""
    for piece in "${all_pieces[@]}"
    do
        [ "${piece}" == "." ] && continue
        if [ "${piece}" == ".." ]
        then
            pushd "${full_path}/.." 2>&1 > /dev/null
            full_piece=$(pwd -P)
            popd 2>&1 > /dev/null
            DEBUG "${full_piece} is a relative parent (..)"
            full_path="${full_piece}"
            continue
        fi
        full_piece="${full_path}/${piece}"
        if [ -L "${full_piece}" ]
        then
            if [ -d "${full_piece}" ]
            then
                pushd "${full_piece}" 2>&1 > /dev/null
                link_path=$(pwd -P)
                popd 2>&1 > /dev/null
                DEBUG "${full_piece} is a path symlink to ${link_path}"
                full_path="${link_path}"
            else
                link_path=$(stat --format="%N" "${full_piece}" \
                                   | perl -pe 's!^.+?\-\> ‘(.+?)’\s*$!$1!;' )
                DEBUG "${full_piece} is a file symlink to ${link_path}"
                full_path="${link_path}"
            fi
            continue
        fi
        if [ -d "${full_piece}" ]
        then
            full_path="${full_piece}"
            DEBUG "${full_path} is a directory"
            continue
        fi
        if [ -f "${full_piece}" ]
        then
            full_path="${full_piece}"
            DEBUG "${full_path} is a file"
            continue
        fi
        # from this point forward, things don't exist
        DEBUG "${full_piece} does not exist"
        full_path="${full_piece}"
    done
    export EXPANDED_PATH="${full_path}"
}

declare -a OUTPUT_QUEUE
function queue_output() {
    IDX=${#OUTPUT_QUEUE[@]}
    OUTPUT_QUEUE[${IDX}]="$1"
}

function output_queue() {
    for item in "${OUTPUT_QUEUE[@]}"
    do
        if [ $G_NULL_TERMINATE -eq 1 ]
        then
            printf '%s%b' "${item}" '\0'
        else
            echo "${item}"
        fi
    done
}

#
# Main Function
#

function main() {
    typeset -i I
    for ((I=0; I<${#TARGET_PATHS[@]}; I++))
    do
        this_path="${TARGET_PATHS[${I}]}"
        DEBUG "Processing: ${this_path}"
        expand_abspath "${this_path}"
        queue_output "${EXPANDED_PATH}"
    done
    output_queue
    return 0
}

#
# Command Line Processing
#

IDX=0
while [ $# -gt 0 ]
do
    OPTION="$1"
    OPTARG="$2"
    case "${OPTION}" in
        "-z"|"--null") G_NULL_TERMINATE=1;;
        #"-q"|"--quiet") G_VERBOSITY=$V_QUIET;;
        "-v"|"--verbose") G_VERBOSITY=$((G_VERBOSITY+1));;
        "-h"|"--help") display_usage;;
        *)
            # options start with a '-'
            echo "${OPTION}" | egrep -q '^\s*\-'
            [ $? -eq 0 ] && display_usage "Unknown option \"${OPTION}\""
            # assume everything else is the path?
            TARGET_PATHS[$IDX]=${OPTION}
            IDX=$((IDX+1))
            ;;
    esac
    shift
done

# Kickoff
main ; exit $?