Some commands you type in the shell are actually not binaries but shell (bash for example) buitins. For example, “alias” is such an shell builtin.
~# type alias
alias is a shell builtin
~# man alias
No manual entry for alias
In order to obtain more information about the “alias” builtin, you should type “man bash” and search what you are looking for in the hundreds of pages long man.
However, there is a quicker way! “help” helps you:
~# help alias
alias: alias [-p] [name[=value] … ]
Define or display aliases.
Without arguments, `alias’ prints the list of aliases in the reusable
form `alias NAME=VALUE’ on standard output.
Otherwise, an alias is defined for each NAME whose VALUE is given.
A trailing space in VALUE causes the next word to be checked for
alias substitution when the alias is expanded.
-p Print all defined aliases in a reusable format
alias returns true unless a NAME is supplied for which no alias has been