[This function has been superseded by the tie() function.]
-This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to a
+This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a
hash. HASH is the name of the hash. (Unlike normal open, the first
argument is I<NOT> a filehandle, even though it looks like one). DBNAME
is the name of the database (without the F<.dir> or F<.pag> extension if
returns FALSE only if the command does not exist I<and> it is executed
directly instead of via your system's command shell (see below).
+Since it's a common mistake to use system() instead of exec(), Perl
+warns you if there is a following statement which isn't die(), warn()
+or exit() (if C<-w> is set - but you always do that). If you
+I<really> want to follow an exec() with some other statement, you
+can use one of these styles to avoid the warning:
+
+ exec ('foo') or print STDERR "couldn't exec foo";
+ { exec ('foo') }; print STDERR "couldn't exec foo";
+
If there is more than one argument in LIST, or if LIST is an array with
more than one value, calls execvp(3) with the arguments in LIST. If
there is only one scalar argument, the argument is checked for shell
=item format
-Declare a picture format with use by the write() function. For
+Declare a picture format for use by the write() function. For
example:
format Something =
to modify the elements of the array. While this is useful and
supported, it can cause bizarre results if the LIST is not a named
array. Similarly, grep returns aliases into the original list,
-much like the way that L<Foreach Loops>'s index variable aliases the list
+much like the way that a for loops's index variable aliases the list
elements. That is, modifying an element of a list returned by grep
(for example, in a C<foreach>, C<map> or another C<grep>)
actually modifies the element in the original list.
list must be placed in parentheses. See L<perlsub/"Temporary Values via
local()"> for details, including issues with tied arrays and hashes.
-But you really probably want to be using my() instead, because local() isn't
-what most people think of as "local"). See L<perlsub/"Private Variables
+You really probably want to be using my() instead, because local() isn't
+what most people think of as "local". See L<perlsub/"Private Variables
via my()"> for details.
=item localtime EXPR
to make it easy to load standard modules. This form of loading of
modules does not risk altering your namespace.
-For a yet-more-powerful import facility, see L</use> and
-L<perlmod>.
+In other words, if you try this:
+
+ require Foo::Bar ; # a splendid bareword
+
+The require function will actually look for the "Foo/Bar.pm" file in the
+directories specified in the @INC array.
+
+But if you try this :
+
+ $class = 'Foo::Bar';
+ require $class ; # $class is not a bareword
+or
+ require "Foo::Bar" ; # not a bareword because of the ""
+
+The require function will look for the "Foo::Bar" file in the @INC array and
+will complain about not finding "Foo::Bar" there. In this case you can do :
+
+ eval "require $class";
+
+For a yet-more-powerful import facility, see L</use> and L<perlmod>.
=item reset EXPR
For delays of finer granularity than one second, you may use Perl's
syscall() interface to access setitimer(2) if your system supports it,
-or else see L</select()> below.
+or else see L</select()> above.
See also the POSIX module's sigpause() function.
matching PATTERN is taken to be a delimiter separating the fields. (Note
that the delimiter may be longer than one character.)
-If LIMIT is specified and is not negative, splits into no more than
-that many fields (though it may split into fewer). If LIMIT is
-unspecified, trailing null fields are stripped (which potential users
+If LIMIT is specified and is positive, splits into no more than that
+many fields (though it may split into fewer). If LIMIT is unspecified
+or zero, trailing null fields are stripped (which potential users
of pop() would do well to remember). If LIMIT is negative, it is
treated as if an arbitrarily large LIMIT had been specified.
ID, among other things. In versions of Perl prior to 5.004 the default
seed was just the current time(). This isn't a particularly good seed,
so many old programs supply their own seed value (often C<time ^ $$> or
-C<time ^ ($$ + ($$ << 15))>), but that isn't necessary any more.
+C<time ^ ($$ + ($$ E<lt>E<lt> 15))>), but that isn't necessary any more.
In fact, it's usually not necessary to call srand() at all, because if
it is not called explicitly, it is called implicitly at the first use of
value: the CODE ref of the closure you just created. See L<perlsub> and
L<perlref> for details.
+=item substr EXPR,OFFSET,LEN,REPLACEMENT
+
=item substr EXPR,OFFSET,LEN
=item substr EXPR,OFFSET
keep the string the same length you may need to pad or chop your value
using sprintf().
+An alternative to using substr() as an lvalue is to specify the
+replacement string as the 4th argument. This allows you to replace
+parts of the EXPR and return what was there before in one operation.
+In this case LEN can be C<undef> if you want to affect everything to
+the end of the string.
+
=item symlink OLDFILE,NEWFILE
Creates a new filename symbolically linked to the old filename.
If the system call fails, syscall returns -1 and sets C<$!> (errno).
Note that some system calls can legitimately return -1. The proper
way to handle such calls is to assign C<$!=0;> before the call and
-check the value of <$!> if syscall returns -1.
+check the value of C<$!> if syscall returns -1.
There's a problem with C<syscall(&SYS_pipe)>: it returns the file
number of the read end of the pipe it creates. There is no way
system() on a Unix system to check for all possibilities, including for
signals and core dumps.
- $rc = 0xffff & system @args;
+ $! = 0;
+ $rc = system @args;
printf "system(%s) returned %#04x: ", "@args", $rc;
if ($rc == 0) {
print "ran with normal exit\n";
}
elsif ($rc == 0xff00) {
- print "command failed: $!\n";
+ # Note that $! can be an empty string if the command that
+ # system() tried to execute was not found, not executable, etc.
+ # These errors occur in the child process after system() has
+ # forked, so the errno value is not visible in the parent.
+ printf "command failed: %s\n", ($! || "Unknown system() error");
}
- elsif ($rc > 0x80) {
+ elsif (($rc & 0xff) == 0) {
$rc >>= 8;
print "ran with non-zero exit status $rc\n";
}
=item umask
Sets the umask for the process to EXPR and returns the previous value.
-If EXPR is omitted, merely returns the current umask. Remember that a
+If EXPR is omitted, merely returns the current umask. If umask(2) is
+not implemented on your system, returns C<undef>. Remember that a
umask is a number, usually given in octal; it is I<not> a string of octal
digits. See also L</oct>, if all you have is a string.
projects / p5sagit/p5-mst-13.2.git / blobdiff