X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlvar.pod;h=292f444dfe1291b4f57ae3370ef10f32db8d79ae;hb=53273a086103cdbbf7ebdd5f1a18b2c0777cbc1b;hp=7667f1d75d06eacd371028804fe3b22c9362595b;hpb=54bfe034ba642318cf2c7d0b37579f30adef144a;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlvar.pod b/pod/perlvar.pod index 7667f1d..292f444 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -177,6 +177,11 @@ test. Outside a C test, this will not happen. =back +As C<$_> is a global variable, this may lead in some cases to unwanted +side-effects. As of perl 5.9.1, you can now use a lexical version of +C<$_> by declaring it in a file or in a block with C. Moreover, +declaring C restores the global C<$_> in the current scope. + (Mnemonic: underline is understood in certain operations.) =back @@ -189,10 +194,9 @@ test. Outside a C test, this will not happen. Special package variables when using sort(), see L. Because of this specialness $a and $b don't need to be declared -(using local(), use vars, or our()) even when using the strict -vars pragma. Don't lexicalize them with C or C -if you want to be able to use them in the sort() comparison block -or function. +(using use vars, or our()) even when using the C pragma. +Don't lexicalize them with C or C if you want to be +able to use them in the sort() comparison block or function. =back @@ -471,8 +475,6 @@ taken for something more important.) Consider using "real" multidimensional arrays as described in L. -=item $OFMT - =item $# The output format for printed numbers. This variable is a half-hearted @@ -675,7 +677,7 @@ In the above I stands for anything: zero, non-zero, C. A successful system or library call does B set the variable to zero. -If used an a string, yields the corresponding system error string. +If used as a string, yields the corresponding system error string. You can assign a number to C<$!> to set I if, for instance, you want C<"$!"> to return the string for error I, or you want to set the exit value for the die() operator. (Mnemonic: What just @@ -763,7 +765,9 @@ you may use the CPAN module C. The real uid of this process. (Mnemonic: it's the uid you came I, if you're running setuid.) You can change both the real uid and -the effective uid at the same time by using POSIX::setuid(). +the effective uid at the same time by using POSIX::setuid(). Since +changes to $< require a system call, check $! after a change attempt to +detect any possible errors. =item $EFFECTIVE_USER_ID @@ -777,7 +781,8 @@ The effective uid of this process. Example: ($<,$>) = ($>,$<); # swap real and effective uid You can change both the effective uid and the real uid at the same -time by using POSIX::setuid(). +time by using POSIX::setuid(). Changes to $> require a check to $! +to detect any possible errors after an attempted change. (Mnemonic: it's the uid you went I, if you're running setuid.) C<< $< >> and C<< $> >> can be swapped only on machines @@ -800,7 +805,8 @@ set the real gid. So the value given by C<$(> should I be assigned back to C<$(> without being forced numeric, such as by adding zero. You can change both the real gid and the effective gid at the same -time by using POSIX::setgid(). +time by using POSIX::setgid(). Changes to $( require a check to $! +to detect any possible errors after an attempted change. (Mnemonic: parentheses are used to I things. The real gid is the group you I, if you're running setgid.) @@ -826,6 +832,8 @@ list, say C< $) = "5 5" >. You can change both the effective gid and the real gid at the same time by using POSIX::setgid() (use only a single numeric argument). +Changes to $) require a check to $! to detect any possible errors +after an attempted change. (Mnemonic: parentheses are used to I things. The effective gid is the group that's I for you, if you're running setgid.) @@ -838,21 +846,36 @@ and C<$)> can be swapped only on machines supporting setregid(). =item $0 -Contains the name of the program being executed. On some (read: not -all) operating systems assigning to C<$0> modifies the argument area -that the B program sees. Also note that depending on the platform, -the maximum length of C<$0> may be limited to the space occupied by -the original C<$0>. This is more useful as a way of indicating the +Contains the name of the program being executed. + +On some (read: not all) operating systems assigning to C<$0> modifies +the argument area that the C program sees. On some platforms you +may have to use special C options or a different C to see the +changes. Modifying the $0 is more useful as a way of indicating the current program state than it is for hiding the program you're running. (Mnemonic: same as B and B.) +Note that there are platform specific limitations on the the maximum +length of C<$0>. In the most extreme case it may be limited to the +space occupied by the original C<$0>. + +In some platforms there may be arbitrary amount of padding, for +example space characters, after the modified name as shown by C. +In some platforms this padding may extend all the way to the original +length of the argument area, no matter what you do (this is the case +for example with Linux 2.2). + Note for BSD users: setting C<$0> does not completely remove "perl" -from the ps(1) output. For example, setting C<$0> to C<"foobar"> will -result in C<"perl: foobar (perl)">. This is an operating system feature. +from the ps(1) output. For example, setting C<$0> to C<"foobar"> may +result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix +and the " (perl)" suffix are shown depends on your exact BSD variant +and version). This is an operating system feature, Perl cannot help it. In multithreaded scripts Perl coordinates the threads so that any thread may modify its copy of the C<$0> and the change becomes visible -to ps(1) (assuming the operating system plays along). +to ps(1) (assuming the operating system plays along). Note that the +the view of C<$0> the other threads have will not change since they +have their own copies of it. =item $[ @@ -1063,6 +1086,10 @@ Provide informative "file" names for evals based on the place they were compiled Provide informative names to anonymous subroutines based on the place they were compiled. +=item 0x400 + +Debug assertion subroutines enter/exit. + =back Some bits may be relevant at compile-time only, some at @@ -1317,24 +1344,11 @@ Be sure not to use a bareword as the name of a signal handler, lest you inadvertently call it. If your system has the sigaction() function then signal handlers are -installed using it. This means you get reliable signal handling. If -your system has the SA_RESTART flag it is used when signals handlers are -installed. This means that system calls for which restarting is supported -continue rather than returning when a signal arrives. If you want your -system calls to be interrupted by signal delivery then do something like -this: - - use POSIX ':signal_h'; - - my $alarm = 0; - sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 } - or die "Error setting SIGALRM handler: $!\n"; - -See L. +installed using it. This means you get reliable signal handling. -The delivery policy of signals changed in Perl 5.8.0 from immediate -(also known as "unsafe") to deferred, also known as "safe signals". -See L for more information. +The default delivery policy of signals changed in Perl 5.8.0 from +immediate (also known as "unsafe") to deferred, also known as +"safe signals". See L for more information. Certain internal hooks can be also set using the %SIG hash. The routine indicated by C<$SIG{__WARN__}> is called when a warning message is