coreutils: Common options

 
 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.
 
    Most programs that accept long options recognize unambiguous
 abbreviations of those options.  For example, ‘rmdir
 --ignore-fail-on-non-empty’ can be invoked as ‘rmdir --ignore-fail’ or
 even ‘rmdir --i’.  Ambiguous options, such as ‘ls --h’, are identified
 as such.
 
    Some of these programs recognize the ‘--help’ and ‘--version’ options
 only when one of them is the sole command line argument.  For these
 programs, abbreviations of the long options are not always recognized.
 
 ‘--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 a file operand, and some tools treat it as standard
 input, or as standard output if that is clear from the context.  For
 example, ‘sort -’ reads from standard input, and is equivalent to plain
 ‘sort’.  Unless otherwise specified, a ‘-’ can appear as any operand
 that requires a file name.
 

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