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Re: "The `-a', `-o', `(', and `)' operands are not portable": please cla

From: Paolo Bonzini
Subject: Re: "The `-a', `-o', `(', and `)' operands are not portable": please clarify
Date: Wed, 12 Aug 2009 12:12:43 +0200
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On 08/12/2009 02:37 AM, Reuben Thomas wrote:
2009/8/7 Paolo Bonzini<address@hidden>:
AS_INIT ensures that you can define shell functions normally using

  foo () {
    # body

Alternatively, there is AS_REQUIRE_SHELL_FN that provides a way to define
shell functions from within a m4 macro,

So when should one use AS_INIT, and when should one prefer AS_REQUIRE _SHELL_FN?

It's different things.

AS_INIT initializes m4sh, including ensuring that the current shell supports functions. After that you can define shell functions with the normal syntax.

If you write a m4sh script, you can then define shell functions normally using shell syntax. Even if write a library like Autotest, shell functions that are always needed can be defined normally using shell syntax.

AS_REQUIRE_SHELL_FN is a separate thing. It provides a convenience for defining a shell function, and will expand the function definition just once. Also, the function definition will be placed early in the file, just after the initialization code.

AS_REQUIRE_SHELL_FN is useful if you do not know in advance which functions will be needed, or what code they will expand to.

For example, AC_CHECK_FUNC does two things: 1) it uses AS_REQUIRE_SHELL_FN to generate a shell function with the test code, and 2) it produces a call to the function. The call ends up where AC_CHECK_FUNC was in the configure.ac file, while the shell function is placed early in the configure script.

AC_CHECK_FUNC uses AS_REQUIRE_SHELL_FN because Autoconf scripts may not all need the check-function test code, and because the body of the function is not known, say, when AC_INIT is executed (because it depends on the language being tested).


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