What are .in files?

Question

Sometimes in the sources of projects I see "*.in" files. For example, a bunch of "Makefile.in"s. What are they for and/or what does the ".in" part mean? I assume that this has something to do with autoconf or make or something like those, but I'm not sure.

I've tried searching for ".in file extension", "autoconf .in file extension", "autoconf .in", "autoconf dot in", and other variants, with no luck.

If you want to know how autotools work, I suggest this series of articles: http://www.freesoftwaremagazine.com/articles/gnu_coding_standards_applied_to_autotools. — Boris Burkov, Jul 25 '13 at 10:04
I found this in my google search. Kinda scary. https://fileinfo.com/extension/in — Bozeyman9000, Oct 23 '18 at 20:28

Trevor Hickey · Answer 1 · 2013-07-25T08:29:46.873

37

I believe the automake process involving a Makefile.in is something like this:

  Makefile.am
       |
      \'/
+--------------+
|   automake   |
+--------------+
       |
      \'/
   Makefile.in
       |
      \'/
+--------------+    +--------------+
| ./configure  |<-- |   autoconf   |<-- configure.in
+--------------+    +--------------+
       |
      \'/
    Makefile

Nobody actually writes a Makefile.in. The only programmer-defined file here is the Makefile.am.

edited Jul 25 '13 at 08:29

answered Jul 25 '13 at 08:19

Trevor Hickey

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Well, on occasion I've written a `Makefile.in`, because automake wouldn't do what I want. – Simon Richter Jul 25 '13 at 14:03

score 29 · Accepted Answer · answered Jul 25 '13 at 07:43

29

it's just a convention that signifies the given file is for input; in my experience, these files tend to be a sort of generic template from which a specific output file or script results.

answered Jul 25 '13 at 07:43

Josh McGee

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Out of interest, could you cite some examples where ".in" is used in this way outside of the `autoconf` realm? – spinkus Jul 05 '14 at 12:08
@spinkus Python packaging/dev tools use it now, e.g. `MANIFEST.in` and `requirements.in`. The former name would have been in use back in 2014 when you first asked! – shadowtalker Sep 30 '22 at 20:28

score 9 · Answer 3 · answered Jul 25 '13 at 09:56

9

They are input files for the m4 macro preprocessor. Among other things, these files contain macros marked by @, that get expanded by m4.

answered Jul 25 '13 at 09:56

ninjalj

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Nope. `Makefile.in` is never touched by anything `m4` related. – Simon Richter Jul 25 '13 at 14:02

What are .in files?

3 Answers3

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