The Get Line from SYS$COMMAND routine gets one record of ASCII
    text from the current controlling input device, specified by the
    logical name SYS$COMMAND.

    Format

      LIB$GET_COMMAND  resultant-string [,prompt-string]

                       [,resultant-length]

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Arguments

 resultant-string

    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor

    String that LIB$GET_COMMAND gets from SYS$COMMAND. The resultant-
    string argument is the address of a descriptor pointing to this
    string.

 prompt-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Prompt message that LIB$GET_COMMAND displays on the controlling
    terminal. The prompt-string argument is the address of a
    descriptor pointing to the prompt. Any string can be a valid
    prompt. By convention however, a prompt string 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.

 resultant-length

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by reference

    Number of bytes written into resultant-string by LIB$GET_
    COMMAND, not counting padding in the case of a fixed string.
    The resultant-length argument is the address of an unsigned word
    containing this length. If the input string is truncated to the
    size specified in the resultant-string descriptor, resultant-
    length is set to this size. Therefore, resultant-length can
    always be used by the calling program to access a valid substring
    of resultant-string.