EECS 1012 Lecture Notes - Lecture 29: Operand
13 Jun 2018
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EECS 1012 Lecture 29 Notes
Introduction
Positional operands
• Positional operands require the operand to be located in a particular position within the
line.
• For example, in the Windows command COPY SOURCE-FILE DESTINATION the first
operand, SOURCE-FILE, positionally specifies the path name of the file to be copied.
• The second operand, DESTINATION, which is optional, specifies either a new name for
the file or the path name of a directory to which the file is to be copied.
• If the seond operand is asent, the diretory to whih the user is urrently attahed
is used.
• The importance of the position of these positional operands is obvious: some older
operating systems specified the destination operand first
• Reversing the position could destroy the file to be copied. Keyword operands are
identified by the use of a particular keyword.
• In many systems, the keyword is accompanied by a modifier symbol that identifies the
operand as a keyword as opposed to a file name.
• The keyword identifies the purpose of the operand.
• Keyword operands are frequently used as optional operands, sometimes with a
particular positional value attached.
• In some systems, keyword operands and modifiers can be placed anywhere after the
command without affecting the positions of positional operands.
• In other systems, the keyword operands, if present, must be placed in a particular
position.
• The slash mark (/) in Windows and hyphen (-) in Linux are examples of modifier symbols.
Keyword operands are sometimes known as switches or modifiers.
• The Windows command MODE COM1 BAUD=2400 PARITY=N DATABITS=8 uses the
positional operand COM1 to identify a particular communications port or other device.
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