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COMMAND is the name of the command for which to add a completion

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SHORT_OPTION is a one character option for the command

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LONG_OPTION is a multi character option for the command

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OPTION_ARGUMENTS is parameter containing a space-separated list of possible option-arguments, which may contain subshells

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DESCRIPTION is a description of what the option and/or option arguments do

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-C STRING or --do-complete=STRING makes complete try to find all possible completions for the specified string

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-e or --erase implies that the specified completion should be deleted

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-f or --no-files specifies that the option specified by this completion may not be followed by a filename

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-n or --condition specifies a shell command that must return 0 if the completion is to be used. This makes it possible to specify completions that should only be used in some cases.

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-o or --old-option implies that the command uses old long style options with only one dash

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-p or --path implies that the string COMMAND is the full path of the command

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-r or --require-parameter specifies that the option specified by this completion always must have an option argument, i.e. may not be followed by another option

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-u or --unauthorative implies that there may be more options than the ones specified, and that fish should not assume that options not listed are spelling errors

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-A or --authorative implies that there may be no more options than the ones specified, and that fish should assume that options not listed are spelling errors

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-x or --exclusive implies both -r and -f

Command specific tab-completions in fish are based on the notion of options and arguments. An option is a parameter which begins with a hyphen, such as '-h', '-help' or '--help'. Arguments are parameters that do not begin with a hyphen. Fish recognizes three styles of options, the same styles as the GNU version of the getopt library. These styles are:

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Short options, like '-a'. Short options are a single character long, are preceded by a single hyphen and may be grouped together (like '-la', which is equivalent to '-l -a'). Option arguments may be specified in the following parameter ('-w 32') or by appending the option with the value ('-w32').

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Old style long options, like '-Wall'. Old style long options can be more than one character long, are preceded by a single hyphen and may not be grouped together. Option arguments are specified in the following parameter ('-ao null').

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GNU style long options, like '--colors'. GNU style long options can be more than one character long, are preceded by two hyphens, and may not be grouped together. Option arguments may be specified in the following parameter ('--quoting-style shell') or by appending the option with a '=' and the value ('--quoting-style=shell'). GNU style long options may be abbreviated so long as the abbreviation is unique ('--h' is equivalent to '--help' if help is the only long option beginning with an 'h').

The options for specifying command name, command path, or command switches may all be used multiple times to specify multiple commands which have the same completion or multiple switches accepted by a command.

When erasing completions, it is possible to either erase all completions for a specific command by specifying complete -e -c COMMAND, or by specifying a specific completion option to delete by specifying either a long, short or old style option.

The short style option -d for the grep command requires that one of the strings 'read', 'skip' or 'recurse' is used. This can be specified writing complete -c grep -s d -x -a 'read skip recurse'.

The su command takes any username as an argument. Usernames are given as the first colon-separated field in the file /etc/passwd. This can be specified as: complete -x -c su -d 'Username' -a '(cat /etc/passwd|cut -d : -f 1)' .

The rpm command has several different modes. If the -e or --erase flag has been specified, rpm should delete one or more packages, in which case several switches related to deleting packages are valid, like the nodeps switch.

This can be written as:

complete -c rpm -n '__fish_contains_opt -s e erase' -l nodeps -d 'Don't check dependencies'

where __fish_contains_opt is a function that checks the commandline buffer for the presence of a specified set of options.