Viewing information for Bash built-ins

help <command>

This will display the Bash help (manual) page for the specified built-in.

For example, help unset will show:

unset: unset [-f] [-v] [-n] [name ...]
 Unset values and attributes of shell variables and functions.

 For each NAME, remove the corresponding variable or function.

 Options:
 -f treat each NAME as a shell function
 -v treat each NAME as a shell variable
 -n treat each NAME as a name reference and unset the variable itself
 rather than the variable it references

 Without options, unset first tries to unset a variable, and if that fails,
 
 tries to unset a function.

 Some variables cannot be unset; also see `readonly'.

Exit Status:
Returns success unless an invalid option is given or a NAME is read-only.

To see a list of all built-ins with a short description, use

help -d