( Testing Values and Files

Info Catalog ( Portable Shell ( Writing Tests ( Multiple Cases
 5.6 Testing Values and Files
 `configure' scripts need to test properties of many files and strings.
 Here are some portability problems to watch out for when doing those
    The `test' program is the way to perform many file and string tests.
 It is often invoked by the alternate name `[', but using that name in
 Autoconf code is asking for trouble since it is an `m4' quote character.
    If you need to make multiple checks using `test', combine them with
 the shell operators `&&' and `||' instead of using the `test' operators
 `-a' and `-o'.  On System V, the precedence of `-a' and `-o' is wrong
 relative to the unary operators; consequently, POSIX does not specify
 them, so using them is nonportable.  If you combine `&&' and `||' in
 the same statement, keep in mind that they have equal precedence.
    To enable `configure' scripts to support cross-compilation, they
 shouldn't do anything that tests features of the host system instead of
 the target system.  But occasionally you may find it necessary to check
 whether some arbitrary file exists.  To do so, use `test -f' or `test
 -r'.  Do not use `test -x', because 4.3BSD does not have it.
    Another nonportable shell programming construction is
    The intent is to set VAR to VALUE only if it is not already set, but
 if VAR has any value, even the empty string, to leave it alone.  Old
 BSD shells, including the Ultrix `sh', don't accept the colon, and
 complain and die.  A portable equivalent is
      : ${VAR=VALUE}
Info Catalog ( Portable Shell ( Writing Tests ( Multiple Cases
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