Portability problems can be difficult to characterize since they span the entire spectrum from a total paradigm shift (such as traditional Mac OS versus System V Unix) to almost trivial bug fixes (such as a fix to a bug in the error exit status of a program). Nevertheless, here are some common portability problems that every makefile must deal with sooner or later:
Program names
It is quite common for various platforms to use different names for the same or similar programs. The most common is the name of the C or C++ compiler (e.g., cc , xlc ). It is also common for GNU versions of programs to be installed on a non-GNU system with the g prefix (e.g., gmake , gawk ).
Paths
The location of programs and files often varies between platforms. For instance, on Solaris systems the X directories are stored under /usr/X while on many other systems the path is /usr/X11R6 . In addition, the distinction between /bin , /usr/bin , /sbin , and /usr/sbin is often rather fuzzy as you move from one system to another.
Options
The command-line options to programs vary, particularly when an alternate implementation is used. Furthermore, if a platform is missing a utility or comes with a broken version, you may need to replace the utility with another that uses different command-line options.
Shell features
By default, make executes command scripts with /bin/sh , but sh implementations vary widely in their features. In particular, pre-POSIX shells are missing many features and will not accept the same syntax as a modern shell.
The Open Group has a very useful white paper on the differences between the System V shell and the POSIX shell. It can be found at http://www.unix-systems.org/whitepapers/shdiffs.html. For those who want more details, the specification of the POSIX shell's command language can be found at http://www.opengroup.org/onlinepubs/007904975/utilities/xcu_chap02.html.
Program behavior
Portable makefile s must contend with programs that simply behave differently. This is very common as different vendors fix or insert bugs and add features. There are also upgrades to utilities that may or may not have made it into a vendor's release. For instance, in 1987 the awk program underwent a major revision. Nearly 20 years later, some systems still do not install this upgraded version as the standard awk .
Operating system
Finally, there are the portability problems associated with a completely different operating system such as Windows versus Unix or Linux versus VMS.
