input -- read input from the user (or from a file) and assign it to a variable
input "Hello" a
input #1 a$
input reads the new contents of one or many (numeric- or string-) variables, either from the keyboard (i.e. from you) or from a file. An optional first string-argument specifies a prompt, which will be issued before reading any contents.
If you want to read from an open file, you need to specify a hash ('#'), followed by the number, under which the file has been opened.
Note, that the input is split at spaces, i.e. if you enter a whole line consisting of many space-seperated word, the first input-statement will only return the first word; the other words will only be returned on subsequent calls to input; the same applies, if a single input reads multiple variables: The first variable gets only the first word, the second one the second word, and so on. If you don't like this behaviour, you may use line input, which returns a whole line (including embedded spaces) at once.
input "Please enter the name of a file to read: " a$
input #1 b$
If this program is stored within a file test.yab and you enter this name when prompted for a file to read, you will see this output:
Please enter the name of a file to read: test.yab