Can an alias be added to the dock via the command line

mkalias is a binary available in a set of tools here. It can also be installed via Homebrew with brew install osxutils.

This is a SH shell script that calls AppleScript to create an alias.

I'm including the shell script here for future reference incase it goes missing from the nets.

#!/bin/sh

# make_alias
# This script takes two command-line arguments:
# 1) The name (relative or full path) of a source file or folder (directory)
# 2) The name (relative or full path) of a destination folder (directory)
# The script makes a Finder-style alias to the source file or folder
# and puts it in the specified destination folder.
#
# Cameron Hayne (macdev@hayne.net), December 2003
# Modified as suggested by Paul Russell (prussell@sonic.net), May 2006
#          to allow either file or folder as source
# Mofified to work with ".app" files, January 2007

scriptname=`basename $0`
if [ $# -lt 2 ]; then
    echo "Usage: $scriptname srcPath destPath"
    exit
fi

srcPath=$1
destPath=$2

if [ ! -e "$srcPath" ]; then
    echo "$scriptname: $srcPath: No such file or directory"
    exit
fi

# remove possible trailing slash from $srcPath
srcPath=${srcPath%/}

# set $srcType to "file" or "folder" as appropriate
if [ -d "$srcPath" ]; then
    if [ "${srcPath##*.}" == "app" ]; then
        srcType="file"
    else
        srcType="folder"
    fi
else
    srcType="file"
fi

# check if the $destPath directory exists
if [ ! -d "$destPath" ]; then
    echo "$scriptname: $destPath: No such directory"
    exit
fi

# check if we have permission to create a new file in the $destPath directory
if [ ! -w "$destPath" ]; then
    echo "$scriptname: No write permission in the directory $destPath"
    exit
fi

case $srcPath in
/*) fullSrcPath=$srcPath ;;
~*) fullSrcPath=$srcPath ;;
*)  fullSrcPath=`pwd`/$srcPath ;;
esac

case $destPath in
/*) fullDestPath=$destPath ;;
~*) fullDestPath=$destPath ;;
*)  fullDestPath=`pwd`/$destPath ;;
esac

/usr/bin/osascript > /dev/null <<EOT
tell application "Finder"
    set macSrcPath to POSIX file "$fullSrcPath" as text
    set macDestPath to POSIX file "$fullDestPath" as text
    make new alias file to $srcType macSrcPath at folder macDestPath
end tell
EOT

The information is accessible through dscl. To add the alias "visitor" and be able to use this username for guest login, use the following command:

sudo dscl . -merge Users/Guest RecordName visitor