¿Puedo crear un acceso directo/alias a una carpeta desde el terminal?

Es posible hacerlo en una línea de Terminal. Digamos que quieres poner un alias al archivo "/Users/me/Library/Preferences/org.herf.Flux.plist".

osascript -e 'tell application "Finder"' -e 'make new alias to file (posix file "/Users/me/Library/Preferences/org.herf.Flux.plist") at desktop' -e 'end tell'

Debe reemplazar to file con to folder si tiene una carpeta.

Aquí hay un shell script que permite pasar una ruta de archivo o carpeta para crear el alias:

#!/bin/bash

if [[ -f "$1" ]]; then
  type="file"
else
  if [[ -d "$1" ]]; then 
    type="folder"
  else
    echo "Invalid path or unsupported type"
    exit 1
  fi
fi

osascript <<END_SCRIPT
tell application "Finder"
   make new alias to $type (posix file "$1") at desktop
end tell
END_SCRIPT

Si nombras este script make-alias.sh , chmod u+x make-alias.sh y ponerlo en /usr/local/bin puede ejecutar, por ejemplo make-alias.sh ~/Library/Preferences .

#!/bin/bash

get_abs() {
  # $1 : relative filename
  echo "$(cd "$(dirname "$1")" && pwd)/$(basename "$1")"
}

if [[ $# -ne 2 ]]; then
    echo "mkalias: specify 'from' and 'to' paths" >&2
    exit 1
fi

from=$(eval get_abs $1)  
todir=$(dirname $(eval get_abs $2))
toname=$(basename $(eval get_abs $2))
if [[ -f "$from" ]]; then
    type="file"
elif [[ -d "$from" ]]; then
    type="folder"
else
    echo "mkalias: invalid path or unsupported type: '$from'" >&2
    exit 1
fi

osascript <<EOF
tell application "Finder"
   make new alias to $type (posix file "$from") at (posix file "$todir")
   set name of result to "$toname"
end tell
EOF

En caso de que necesite dirigir el enlace a una carpeta específica (o darle un nombre específico), puede utilizar set name of result to "…" como en

#!/bin/bash

if [[ $# -ne 2 ]]; then
    echo "mkalias: specify 'from' and 'to' paths" >&2
    exit 1
fi

from="$(realpath $1)"
todir="$(dirname $(realpath $2))"
toname="$(basename $(realpath $2))"
if [[ -f "$from" ]]; then
    type="file"
elif [[ -d "$from" ]]; then
    type="folder"
else
    echo "mkalias: invalid path or unsupported type: '$from'" >&2
    exit 1
fi

osascript <<EOF
tell application "Finder"
   make new alias to $type (posix file "$from") at (posix file "$todir")
   set name of result to "$toname"
end tell
EOF

Para la gente que quiera una solución en Python, aquí hay una función que envuelve a applescript y luego llama a subprocess.call:

def applescript_finder_alias(theFrom, theTo):
    """
    (theFrom, theTo)
    create a short/alias
    theFrom, theTo: relative or abs path, both folder or both file
    """
    # https://apple.stackexchange.com/questions/51709
    applescript = '''
    tell application "Finder"
       make new alias to %(theType)s (posix file "%(theFrom)s") at (posix file "%(todir)s")
       set name of result to "%(toname)s"
    end tell
    '''
    def myesp(cmdString):
        import os, inspect, tempfile, subprocess
        caller = inspect.currentframe().f_back
        cmd =  cmdString % caller.f_locals

        fd, path = tempfile.mkstemp(suffix='.applescript')
        try:
            with os.fdopen(fd, 'w') as tmp:
                tmp.write(cmd.replace('"','\"').replace("'","\'")+'\n\n')
            subprocess.call('osascript ' + path, shell=True, executable="/bin/bash")
        finally:
            os.remove(path)
        return None
    import os
    theFrom = os.path.abspath(theFrom)
    theTo = os.path.abspath(theTo)
    if os.path.isfile(theFrom): 
        theType = 'file'
    else:
        theType = 'folder'
    todir = os.path.dirname(theTo)
    toname = os.path.basename(theTo)
    myesp(applescript)