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I found this accidentally.

I just typed man fork, and instead of showing the system call documentation, it showed to me an awk extension, however, the section page number was 3am, instead of just 3.

What does 3am means?

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  • 11
    'Read it very early in the morning'.
    – bmargulies
    Commented Mar 25, 2019 at 21:54
  • 3
    My first thought was something like unix.stackexchange.com/questions/405783/…
    – user2752467
    Commented Mar 26, 2019 at 7:18
  • @bmargulies And read CPAN::Queue (3pm) before afternoon tea; sorry, I missed the joke initially.
    – U. Windl
    Commented Apr 5, 2022 at 8:07

2 Answers 2

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18

It appears to be the manual page for a GNU Awk (gawk) extension module. The complete list is:

$ find /usr/share/man/man3 -name '*3am*' | xargs dpkg -S
gawk: /usr/share/man/man3/readfile.3am.gz
gawk: /usr/share/man/man3/inplace.3am.gz
gawk: /usr/share/man/man3/ordchr.3am.gz
gawk: /usr/share/man/man3/revoutput.3am.gz
gawk: /usr/share/man/man3/readdir.3am.gz
gawk: /usr/share/man/man3/filefuncs.3am.gz
gawk: /usr/share/man/man3/revtwoway.3am.gz
gawk: /usr/share/man/man3/time.3am.gz
gawk: /usr/share/man/man3/rwarray.3am.gz
gawk: /usr/share/man/man3/fork.3am.gz
gawk: /usr/share/man/man3/fnmatch.3am.gz

I would guess the am stands for awk module.

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  • 1
    In general, section 3 of the manual contains entries for library calls, which seems appropriate for gawk libraries, whereas fork() is carried out by the kernel and is therefore documented in section 2.
    – Kusalananda ♦
    Commented Mar 25, 2019 at 13:30
  • 2
    Yeah it seems that some libraries or "man page extensions" adds a postfix to the man page section number. In my system I've some prefixes like cpp, ssl or perl.
    – ABu
    Commented Mar 25, 2019 at 15:09
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If you read the middle part of the first line output by man 3am readfile, you'll see:

GNU Awk Extension Modules

Now shouldn't be hard to guess from here, specifically when comparing to other first lines.

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