If set is called with no arguments, the names and values of all shell variables are printed in sorted order. If some of the scope or export flags have been given, only the variables matching the specified scope are printed.
- `-a` or `--append` causes the values to be appended to the current set of values for the variable. This can be used with `--prepend` to both append and prepend at the same time. This cannot be used when assigning to a variable slice.
- `-p` or `--prepend` causes the values to be prepended to the current set of values for the variable. This can be used with `--append` to both append and prepend at the same time. This cannot be used when assigning to a variable slice.
- `-l` or `--local` forces the specified shell variable to be given a scope that is local to the current block, even if a variable with the given name exists and is non-local
- `-U` or `--universal` causes the specified shell variable to be given a universal scope. If this option is supplied, the variable will be shared between all the current users fish instances on the current computer, and will be preserved across restarts of the shell.
- `-q` or `--query` test if the specified variable names are defined. Does not output anything, but the builtins exit status is the number of variables specified that were not defined.
- `-S` or `--show` Shows information about the given variables. If no variable names are given then all variables are shown in sorted order. No other flags can be used with this option. The information shown includes whether or not it is set in each of the local, global, and universal scopes. If it is set in one of those scopes whether or not it is exported is reported. The individual elements are also shown along with the length of each element.
If a variable is set to more than one value, the variable will be an array with the specified elements. If a variable is set to zero elements, it will become an array with zero elements.
If the variable name is one or more array elements, such as `PATH[1 3 7]`, only those array elements specified will be changed. If you specify a negative index when expanding or assigning to an array variable, the index will be calculated from the end of the array. For example, the index -1 means the last index of an array.
-# If a variable is explicitly set to either universal, global or local, that setting will be honored. If a variable of the same name exists in a different scope, that variable will not be changed.
-# If a variable is not explicitly set to be either universal, global or local and has never before been defined, the variable will be local to the currently executing function. Note that this is different from using the `-l` or `--local` flag. If one of those flags is used, the variable will be local to the most inner currently executing block, while without these the variable will be local to the function. If no function is executing, the variable will be global.
-# If a variable is not explicitly set to be exported or not exported, but has been previously defined, the previous exporting rule for the variable is kept.
In erase mode, if variable indices are specified, only the specified slices of the array variable will be erased.
`set` requires all options to come before any other arguments. For example, `set flags -l` will have the effect of setting the value of the variable `flags` to '-l', not making the variable local.
In assignment mode, `set` does not modify the exit status. This allows simultaneous capture of the output and exit status of a subcommand, e.g. `if set output (command)`. In query mode, the exit status is the number of variables that were not found. In erase mode, `set` exits with a zero exit status in case of success, with a non-zero exit status if the commandline was invalid, if the variable was write-protected or if the variable did not exist.
