Node:Portable Shell, Next:Manual Configuration, Previous:Writing Autoconf Macros, Up:Top
When writing your own checks, there are some shell-script programming
techniques you should avoid in order to make your code portable. The
Bourne shell and upward-compatible shells like the Korn shell and Bash
have evolved over the years, but to prevent trouble, do not take
advantage of features that were added after UNIX version 7, circa
1977. You should not use shell functions, aliases, negated character
classes, or other features that are not found in all Bourne-compatible
shells; restrict yourself to the lowest common denominator. Even
unset is not supported by all shells! Also, include a space
after the exclamation point in interpreter specifications, like this:
#! /usr/bin/perl
If you omit the space before the path, then 4.2BSD based systems
(such as Sequent DYNIX) will ignore the line, because they interpret
#! / as a 4-byte magic number. Some old systems have quite
small limits on the length of the #! line too, for instance 32
bytes (not including the newline) on SunOS 4.
The set of external programs you should run in a configure script
is fairly small. See Utilities in Makefiles, for the list. This
restriction allows users to start out with a fairly small set of
programs and build the rest, avoiding too many interdependencies between
packages.
Some of these external utilities have a portable subset of features; see Limitations of Usual Tools.