22.3 Environment
In addition to the problems with portability in shell implementations
discussed in the previous section, the behaviour of the shell can also
be drastically affected by the contents of certain environment
variables, and the operating environment provided by the host machine.
It is important to be aware of the behavior of some of the operating
systems within which your shell script might run. Although not directly
related to the implementation of the shell interpreter, the
characteristics of some of target architectures do influence what is
considered to be portable. To ensure your script will work on as many
shell implementations as possible, you must observe the following
points.
SCO Unix doesn't like LANG=C and friends, but without
LC_MESSAGES=C, Solaris will translate variable values in
set! Similarly, without LC_CTYPE=C, compiled C code can
behave unexpectedly. The trick is to set the values to `C', except
for if they are not already set at all:
| |
for var in LANG LC_ALL LC_MESSAGES LC_CTYPES LANGUAGES
do
if eval test x"\${$var+set}" = xset; then
eval $var=C; eval export $var
fi
done
|
HP-UX ksh and all POSIX shells print the target
directory to standard output if `CDPATH' is set.
| |
if test x"${CDPATH+set}" = xset; then CDPATH=:; export CDPATH; fi
|
The target architecture file system may impose limits on your scripts.
IF you want your scripts to run on the architectures which impose these
limits, then your script must adhere to these limits:
-
The ISO9660 filesystem, as used on most CD-ROMs, limits nesting of
directories to a maximum depth of twelve levels.
-
Many old Unix filesystems place a 14 character limit on the length of
any filename. If you care about portability to DOS,
that has an 8 character limit with an optional extension of 3 or
fewer characters (known as 8.3 notation).
A useful idiom when you need to determine whether a particular pathname
is relative or absolute, which works for DOS targets to follows:
| |
case "$file" in
[\\/]* | ?:[\\/]*) echo absolute ;;
*) echo default ;;
esac
|
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