What does the number in parentheses shown after Unix command names in manpages mean?
It's the section that the man page for the command is assigned to.
These are split as
- General commands
- System calls
- C library functions
- Special files (usually devices, those found in /dev) and drivers
- File formats and conventions
- Games and screensavers
- Miscellanea
- System administration commands and daemons
Original descriptions of each section can be seen in the Unix Programmer's Manual (page ii).
The section the command is documented in the manual. The list of sections is documented on man's manual. For example:
man 1 man
man 3 find
This is useful for when similar or exactly equal commands exist on different sections
The reason why the section numbers are significant is that many years ago when disk space was more of an issue than it is now the sections could be installed individually.
Many systems only had 1 and 8 installed for instance. These days people tend to look the commands up on google instead.