1

With man bc, I have a line starting with bc(1).

bc(1)                                                                    bc(1)

NAME
       bc - An arbitrary precision calculator language

Some of the Unix book also describes Unix commands with (1) attached just like this SO question - https://stackoverflow.com/questions/8402181/how-do-i-get-bc1-to-print-the-leading-zero. What does this mean?

0
3

It's the section number of manual.

From man man:

The table below shows the section numbers of the manual followed by the types of pages they contain.

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 conventions), e.g. man(7), groff(7)
8   System administration commands (usually only for root)
9   Kernel routines [Non standard]

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