The man of Linux can help us to find some helpful information of functions.
This manual is splitted into eight parts.
For example, to see the man of the open() function, you can use the:
$ man 2 open
$ man 3 open
The first will display the man of the Linux Programmer’s Manual.
The second will display the Perl Programmers Reference Guide.
If you want to see all listed mans, use the -k flag.
$ man -k *