I know the difference between legato and shift slide.
but i don't know if:
Is there any difference between glissando and shift/legato slide in guitar?
There isn't really much of a difference. When you shift slide on the guitar, you are trying to get the note as fast as you can while still making it noticeable that you shifted your hand by hitting the notes in between. Shift slides are generally rather fast while a glissando can be drawn out.
Glissandos on guitar (and other instruments too such as piano and banjo) are a little different than how they are on a orchestral string instrument because orchestral string instruments do not have frets so you truly get a pitch bend as you slide up (or down) the fingerboard. As you slide up (or down) a guitar's fretboard, you can't truly get all of the in between notes because the placement of the fret defines the pitch of the note, not your finger. That means it is harder to draw out a glissando on a guitar.
It matters a lot on the piece that you are trying to play as to how you perform a glissando.