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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 (see section 6.7 Systemology).
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 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 section `Utilities in Makefiles' in GNU Coding Standards, 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 10.9 Limitations of Usual Tools.
There are other sources of documentation about shells. See for instance the Shell FAQs.
10.1 Shellology A zoology of shells 10.2 Here-Documents Quirks and tricks 10.3 File Descriptors FDs and redirections 10.4 File System Conventions File- and pathnames 10.5 Shell Substitutions Variable and command expansions 10.6 Assignments Varying side effects of assignments 10.7 Special Shell Variables Variables you should not change 10.8 Limitations of Shell Builtins Portable use of not so portable /bin/sh 10.9 Limitations of Usual Tools Portable use of portable tools 10.10 Limitations of Make Portable Makefiles
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