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I often see command descriptions like this:
Like which(1) Unix command. Find the first instance of an Executable in the PATH. [Source]
Or this:
A cat(1) clone with Wings. [Source]
What are these numbers in parentheses that usually come after the name of some Unix command? It has something to do with the version of the commands?
7
The number in parentheses refers to section of the searched keyword/command.
As the manual is divided into several parts (user commands, system calls, C library functions, devices, file formats and various other topics), there is a need for a disambiguation mechanism.
By default, when you do not specify the section, it refers to section 1 (save some system configuration by determining another _default).
This is found in the "manual of the manual", and it being installed, can be accessed with:
man man
If we were to specify the section (we don’t need it, because command is default option) it would be:
man 1 man
The relevant part of the manual is this:
MANUAL SECTIONS The standard sections of the manual include: 1 User Commands 2 System Calls 3 C Library Functions 4 Devices and Special Files 5 File Formats and Conventions 6 Games et. al. 7 Miscellanea 8 System Administration tools and Daemons
Note that this list can be extended by the authors of each distribution.
If you prefer, you can check this version online:
Note that even in the online version, there is the section number before the topic.
Example of disambiguation:
That in command line would be:
man 1 printf
man 3 printf
In this case note that the first is the command of shell, and the second is from the library’s function C.
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It is the "section" of the command.
– Bacco
No time to write an answer now, but basically: https://superuser.com/q/297702 and https://unix.stackexchange.com/q/3586
– hkotsubo