tar: Long Options

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1 3.3.1 Long Option Style
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1 Each option has at least one "long" (or "mnemonic") name starting with
1 two dashes in a row, e.g., '--list'.  The long names are more clear than
1 their corresponding short or old names.  It sometimes happens that a
1 single long option has many different names which are synonymous, such
1 as '--compare' and '--diff'.  In addition, long option names can be
1 given unique abbreviations.  For example, '--cre' can be used in place
1 of '--create' because there is no other long option which begins with
1 'cre'.  (One way to find this out is by trying it and seeing what
1 happens; if a particular abbreviation could represent more than one
1 option, 'tar' will tell you that that abbreviation is ambiguous and
1 you'll know that that abbreviation won't work.  You may also choose to
1 run 'tar --help' to see a list of options.  Be aware that if you run
1 'tar' with a unique abbreviation for the long name of an option you
1 didn't want to use, you are stuck; 'tar' will perform the command as
1 ordered.)
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1    Long options are meant to be obvious and easy to remember, and their
1 meanings are generally easier to discern than those of their
1 corresponding short options (see below).  For example:
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1      $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0
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1 gives a fairly good set of hints about what the command does, even for
1 those not fully acquainted with 'tar'.
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1    Long options which require arguments take those arguments immediately
1 following the option name.  There are two ways of specifying a mandatory
1 argument.  It can be separated from the option name either by an equal
1 sign, or by any amount of white space characters.  For example, the
1 '--file' option (which tells the name of the 'tar' archive) is given a
1 file such as 'archive.tar' as argument by using any of the following
1 notations: '--file=archive.tar' or '--file archive.tar'.
1 
1    In contrast, optional arguments must always be introduced using an
1 equal sign.  For example, the '--backup' option takes an optional
1 argument specifying backup type.  It must be used as
1 '--backup=BACKUP-TYPE'.
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