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2. Common options

Certain options are available in all of these programs. Rather than writing identical descriptions for each of the programs, they are described here. (In fact, every GNU program accepts (or should accept) these options.)

Normally options and operands can appear in any order, and programs act as if all the options appear before any operands. For example, ‘sort -r passwd -t :’ acts like ‘sort -r -t : passwd’, since ‘:’ is an option-argument of ‘-t’. However, if the POSIXLY_CORRECT environment variable is set, options must appear before operands, unless otherwise specified for a particular command.

A few programs can usefully have trailing operands with leading ‘-’. With such a program, options must precede operands even if POSIXLY_CORRECT is not set, and this fact is noted in the program description. For example, the env command's options must appear before its operands, since in some cases the operands specify a command that itself contains options.

Some of these programs recognize the ‘--help’ and ‘--version’ options only when one of them is the sole command line argument.

--help

Print a usage message listing all available options, then exit successfully.

--version

Print the version number, then exit successfully.

--

Delimit the option list. Later arguments, if any, are treated as operands even if they begin with ‘-’. For example, ‘sort -- -r’ reads from the file named ‘-r’.

A single ‘-’ operand is not really an option, though it looks like one. It stands for standard input, or for standard output if that is clear from the context. For example, ‘sort -’ reads from standard input, and is equivalent to plain ‘sort’, and ‘tee -’ writes an extra copy of its input to standard output. Unless otherwise specified, ‘-’ can appear as any operand that requires a file name.


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