builtin
[ -ds
] [ -f
library ] [ name ... ]ksh93 only. This command allows you to load new built-in commands into the shell at runtime from shared library files.
If no arguments are given, builtin
prints all the built-in command names. With arguments, builtin adds each name as a new built-in command (like cd or pwd). If the name contains a slash, the newly-added built-in version is used only if a path search would otherwise have found a command of the same name. (This allows replacement of system commands with faster, built-in versions.) Otherwise, the built-in command is always found.
-d
Delete the built-in command name.
-f
Load new built-in command from library.
-s
Only print "special" built-ins (those designated as special by POSIX).