How do I escape text in autoconf/m4?

Question

The following code from my configuration.ac file does not work (note the nested square brackets with [default=no]):

AC_ARG_ENABLE(debug,
    [  --enable-debug          build with debugging support [default=no].],
    [DEBUG="$enableval"],
    [DEBUG="no"]
)

How can I escape those brackets?

Autoconf scripts are parsed first by m4 and then by the bourne shell. — user278429, Feb 22 '10 at 04:46

score 24 · Answer 1 · edited Apr 11 '21 at 07:38

24

Found it! From this tutorial:

M4 arguments are quoted with [ and ]. There is NO WAY to escape these, however, you have several options if you wish to insert ['s or ]'s:

Use a `Quadrigraph'. @<:@ gives you [ and @:>@ gives you ].

Balance your quotes. M4 will turn [[]] in to []. Beware of using this in arguments to macros. Sometimes, you need to double quote as well ([[[]]]).

Change the quoting using: changequote(<<,>>) to change the quoting to << and >>. The autoconf documentation (rightly, in my opinion) warns against the (over) use of this, since it can lead to unexpected results.

Avoid [ and ] where ever possible. This is my personal choice.

My new code is therefore:

AC_ARG_ENABLE(debug,
    AS_HELP_STRING(
        [--enable-debug],
        [build with debugging symbols @<:@default=no@:>@]),
    [enable_debug="$enableval"],
    [enable_debug="no"]
)

edited Apr 11 '21 at 07:38

Darren Ng

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answered Feb 22 '10 at 07:21

user278429

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1

You should set your own answer as THE answer then. – Magnus Karlsson Nov 21 '12 at 12:41
Autotools absolutely sucks. – jww Nov 09 '18 at 23:19
The quoted tutorial has a new [home](https://github.com/edrosten/autoconf_tutorial#hello-world). – Per Mildner Mar 16 '20 at 10:17

score 9 · Answer 2 · edited Nov 21 '12 at 12:42

9

Brackets are kind of escape characters, so as you do for '\', you may escape brackets [] with brackets, eg :

AC_ARG_ENABLE(debug, [ --enable-debug build with debugging support [[default=no]].], [DEBUG="$enableval"], [DEBUG="no"] )

Note: [[ ]default=no[ ]] may not work as you expect as m4 should search the end_bracket from the end. It should so be expanded to [ ]default=no[ ].

edited Nov 21 '12 at 12:42

bipen

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answered Nov 21 '12 at 12:22

jbar

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Better to use the 'quadrigraph' escapes, @<:@ and @>:@. – ptomato Nov 22 '12 at 16:16

score -1 · Answer 3 · answered Feb 22 '10 at 04:09

-1

use AC_HELP_STRING

answered Feb 22 '10 at 04:09

Anycorn

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Thanks (that is definitely cleaner) but still the same problem. In <> the "[" and "]" are missing from output. – user278429 Feb 22 '10 at 04:48
2

Why the insistence on square brackets in the output? Use parentheses; it makes your life easier. – Jonathan Leffler Feb 22 '10 at 05:12
For consistency's sake, because other packages I'm using have square brackets in their output :( – user278429 Feb 22 '10 at 07:14
4

`AC_HELP_STRING` been deprecated about half a decade ago. Use `AS_HELP_STRING`. – ndim Apr 10 '10 at 10:49

How do I escape text in autoconf/m4?

3 Answers3