To return a string of m characters from x$ beginning with the nth character.
n must be within the range of 1 to 255.
m must be within the range of 0 to 255.
If m is omitted, or if there are fewer than m characters to the right of n, all rightmost characters beginning with n are returned.
If n > LEN(x$), MID$ function returns a null string.
If m equals 0, the MID$ function returns a null string.
If either n or m is out of range, an "Illegal function call error" is returned.
For more information and examples, see the LEFT$ and RIGHT$ functions.
10 A$="GOOD" 20 B$="MORNING EVENING AFTERNOON" 30 PRINT A$; MID$(B$, 8, 8) RUN GOOD EVENING
Line 30 concatenates (joins) the A$ string to another string with a length of eight characters, beginning at position 8 within the B$ string.