Gets one record of ASCII text from the current controlling input
    device specified by SYS$INPUT.

    Format

      SCA$GET_INPUT  get_string,

                     [,prompt_string]

                     [,output_length]

                     [,user_argument]

1  –  Arguments

 get_string
    type:       character string
    access:     write only
    mechanism:  by descriptor

    Buffer to receive the line read from SYS$INPUT. The string is
    returned by a call to STR$COPY_DX.

 prompt_string
    type:       character string
    access:     read only
    mechanism:  by descriptor

    Prompt message that is displayed on the controlling terminal. A
    valid prompt consists of text followed by a colon (:), a space,
    and no carriage-return/line-feed combination. The maximum size
    of the prompt message is 255 characters. If the controlling input
    device is not a terminal, this argument is ignored.

 output_length
    type:       word
    access:     write only
    mechanism:  by reference

    Word to receive the actual length of the GET-STRING line, not
    counting any padding in the case of a fixed string. If the input
    line was truncated, this length reflects the truncated string.

 user_argument
    type:       _UNSPECIFIED
    access:     read only
    mechanism:  by reference

    User-specified value that was passed to the routine that called
    this action routine.

2  –  Condition Values Returned

    SCA$_NORMAL           An input line was returned.

    Failure completion
    code from LIB$GET_
    INPUT.

3  –  Description

    The SCA$GET_INPUT routine gets one record of ASCII text from the
    current controlling input device specified by SYS$INPUT.