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Why do programs in Unix-like environments have numbers after their name?
I have seen several programs, such as GREP(3) and PING(8), listed in manpages. What is the significance of the digit in ()s?
If you run man man you will see the following information in the man page:
1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conven‐
tions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]
Some names are associated with multiple entries, eg on my system 'sleep' has an entry in section 1 and an entry in section 3. You can specify the one you want with e.g.
man 3 sleep
Sometimes I just guess with
man -a sleep
which displays each entry associated with sleep in turn. I just go through them until I find the one I want. You can also try
man -k sleep
to get a slightly bigger listing of pages involving the term 'sleep'