`ulimit` builtin sets or outputs the resource usage limits of the shell and any processes spawned by it. If a new limit value is omitted, the current value of the limit of the resource is printed; otherwise, the specified limit is set to the new value.
The value of limit can be a number in the unit specified for the resource or one of the special values `hard`, `soft`, or `unlimited`, which stand for the current hard limit, the current soft limit, and no limit, respectively.
If limit is given, it is the new value of the specified resource. If no option is given, then `-f` is assumed. Values are in kilobytes, except for `-t`, which is in seconds and `-n` and `-u`, which are unscaled values. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit.
A hard limit can only be decreased. Once it is set it cannot be increased; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are updated when assigning a new limit value, and the soft limit is used when reporting the current value.
- Fish `ulimit` does not support the `-p` option for getting the pipe size. The bash implementation consists of a compile-time check that empirically guesses this number by writing to a pipe and waiting for SIGPIPE. Fish does not do this because it this method of determining pipe size is unreliable. Depending on bash version, there may also be further additional limits to set in bash that do not exist in fish.
