X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfunc.pod;h=3fd00325975f956309d5d180684717888baebc6e;hb=cf2649810f00335bd657355d81bcc9384a620135;hp=79ebdf9a0ed16e69ea906a85e389f9b489e5f472;hpb=24436e9a6cbac7c6d5f2e80821bf1e4ed98a4663;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod index 79ebdf9..3fd0032 100644 --- a/pod/perlfunc.pod +++ b/pod/perlfunc.pod @@ -25,7 +25,7 @@ with LIST as an argument. Such a list may consist of any combination of scalar arguments or list values; the list values will be included in the list as if each individual element were interpolated at that point in the list, forming a longer single-dimensional list value. -Elements of the LIST should be separated by commas. +Commas should separate elements of the LIST. Any function in the list below may be used either with or without parentheses around its arguments. (The syntax descriptions omit the @@ -139,7 +139,7 @@ C, C, C, C, C, C, C, C, C, C, C, C, C, C, C -=item Keywords related to the control flow of your perl program +=item Keywords related to the control flow of your Perl program C, C, C, C, C, C, C, C, C, C, C, C, C, C @@ -226,7 +226,7 @@ C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, -C, C, C, C, +C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, @@ -337,7 +337,7 @@ following a minus are interpreted as file tests. The C<-T> and C<-B> switches work as follows. The first block or so of the file is examined for odd characters such as strange control codes or characters with the high bit set. If too many strange characters (>30%) -are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file +are found, it's a C<-B> file; otherwise it's a C<-T> file. Also, any file containing null in the first block is considered a binary file. If C<-T> or C<-B> is used on a filehandle, the current IO buffer is examined rather than the first block. Both C<-T> and C<-B> return true on a null @@ -351,7 +351,7 @@ structure of the previous file test (or stat operator) is used, saving a system call. (This doesn't work with C<-t>, and you need to remember that lstat() and C<-l> will leave values in the stat structure for the symbolic link, not the real file.) (Also, if the stat buffer was filled by -a C call, C<-T> and C<-B> will reset it with the results of C). +an C call, C<-T> and C<-B> will reset it with the results of C). Example: print "Can do.\n" if -r $a || -w _ || -x _; @@ -368,7 +368,7 @@ Example: As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file test operators, in a way that C<-f -w -x $file> is equivalent to -C<-x $file && -w _ && -f _>. (This is only syntax fancy : if you use +C<-x $file && -w _ && -f _>. (This is only syntax fancy: if you use the return value of C<-f $file> as an argument to another filetest operator, no special magic will happen.) @@ -394,7 +394,7 @@ value of $^F. See L. =item alarm Arranges to have a SIGALRM delivered to this process after the -specified number of wallclock seconds have elapsed. If SECONDS is not +specified number of wallclock seconds has elapsed. If SECONDS is not specified, the value stored in C<$_> is used. (On some machines, unfortunately, the elapsed time may be up to one second less or more than you specified because of how seconds are counted, and process @@ -547,13 +547,13 @@ This function tells the thingy referenced by REF that it is now an object in the CLASSNAME package. If CLASSNAME is omitted, the current package is used. Because a C is often the last thing in a constructor, it returns the reference for convenience. Always use the two-argument -version if the function doing the blessing might be inherited by a -derived class. See L and L for more about the blessing -(and blessings) of objects. +version if a derived class might inherit the function doing the blessing. +See L and L for more about the blessing (and blessings) +of objects. Consider always blessing objects in CLASSNAMEs that are mixed case. Namespaces with all lowercase names are considered reserved for -Perl pragmata. Builtin types have all uppercase names, so to prevent +Perl pragmata. Builtin types have all uppercase names. To prevent confusion, you may wish to avoid such package names as well. Make sure that CLASSNAME is a true value. @@ -603,6 +603,12 @@ previous time C was called. =item chdir EXPR +=item chdir FILEHANDLE + +=item chdir DIRHANDLE + +=item chdir + Changes the working directory to EXPR, if possible. If EXPR is omitted, changes to the directory specified by C<$ENV{HOME}>, if set; if not, changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the @@ -610,6 +616,10 @@ variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If neither is set, C does nothing. It returns true upon success, false otherwise. See the example under C. +On systems that support fchdir, you might pass a file handle or +directory handle as argument. On systems that don't support fchdir, +passing handles produces a fatal error at run time. + =item chmod LIST Changes the permissions of a list of files. The first element of the @@ -625,6 +635,14 @@ successfully changed. See also L, if all you have is a string. $mode = '0644'; chmod oct($mode), 'foo'; # this is better $mode = 0644; chmod $mode, 'foo'; # this is best +On systems that support fchmod, you might pass file handles among the +files. On systems that don't support fchmod, passing file handles +produces a fatal error at run time. + + open(my $fh, "<", "foo"); + my $perm = (stat $fh)[2] & 07777; + chmod($perm | 0600, $fh); + You can also import the symbolic C constants from the Fcntl module: @@ -710,6 +728,10 @@ successfully changed. $cnt = chown $uid, $gid, 'foo', 'bar'; chown $uid, $gid, @filenames; +On systems that support fchown, you might pass file handles among the +files. On systems that don't support fchown, passing file handles +produces a fatal error at run time. + Here's an example that looks up nonnumeric uids in the passwd file: print "User: "; @@ -742,6 +764,10 @@ chr(0x263a) is a Unicode smiley face. Note that characters from 128 to 255 (inclusive) are by default not encoded in UTF-8 Unicode for backward compatibility reasons (but see L). +Negative values give the Unicode replacement character (chr(0xfffd)), +except under the L pragma, where low eight bits of the value +(truncated to an integer) are used. + If NUMBER is omitted, uses C<$_>. For the reverse, use L. @@ -782,7 +808,8 @@ program exits with non-zero status. (If the only problem was that the program exited non-zero, C<$!> will be set to C<0>.) Closing a pipe also waits for the process executing on the pipe to complete, in case you want to look at the output of the pipe afterwards, and -implicitly puts the exit status value of that command into C<$?>. +implicitly puts the exit status value of that command into C<$?> and +C<${^CHILD_ERROR_NATIVE}>. Prematurely closing the read end of a pipe (i.e. before the process writing to it at the other end has closed it) will result in a @@ -817,8 +844,8 @@ L. =item continue BLOCK -Actually a flow control statement rather than a function. If there is a -C BLOCK attached to a BLOCK (typically in a C or +C is actually a flow control statement rather than a function. If +there is a C BLOCK attached to a BLOCK (typically in a C or C), it is always executed just before the conditional is about to be evaluated again, just like the third part of a C loop in C. Thus it can be used to increment a loop variable, even when the loop has been @@ -858,31 +885,42 @@ function, or use this relation: =item crypt PLAINTEXT,SALT -Encrypts a string exactly like the crypt(3) function in the C library -(assuming that you actually have a version there that has not been -extirpated as a potential munition). This can prove useful for checking -the password file for lousy passwords, amongst other things. Only the -guys wearing white hats should do this. - -Note that L is intended to be a one-way function, much like -breaking eggs to make an omelette. There is no (known) corresponding -decrypt function (in other words, the crypt() is a one-way hash -function). As a result, this function isn't all that useful for -cryptography. (For that, see your nearby CPAN mirror.) - -When verifying an existing encrypted string you should use the -encrypted text as the salt (like C). This allows your code to work with the standard L -and with more exotic implementations. In other words, do not assume -anything about the returned string itself, or how many bytes in -the encrypted string matter. +Creates a digest string exactly like the crypt(3) function in the C +library (assuming that you actually have a version there that has not +been extirpated as a potential munitions). + +crypt() is a one-way hash function. The PLAINTEXT and SALT is turned +into a short string, called a digest, which is returned. The same +PLAINTEXT and SALT will always return the same string, but there is no +(known) way to get the original PLAINTEXT from the hash. Small +changes in the PLAINTEXT or SALT will result in large changes in the +digest. + +There is no decrypt function. This function isn't all that useful for +cryptography (for that, look for F modules on your nearby CPAN +mirror) and the name "crypt" is a bit of a misnomer. Instead it is +primarily used to check if two pieces of text are the same without +having to transmit or store the text itself. An example is checking +if a correct password is given. The digest of the password is stored, +not the password itself. The user types in a password that is +crypt()'d with the same salt as the stored digest. If the two digests +match the password is correct. + +When verifying an existing digest string you should use the digest as +the salt (like C). The SALT used +to create the digest is visible as part of the digest. This ensures +crypt() will hash the new string with the same salt as the digest. +This allows your code to work with the standard L and +with more exotic implementations. In other words, do not assume +anything about the returned string itself, or how many bytes in the +digest matter. Traditionally the result is a string of 13 bytes: two first bytes of the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only -the first eight bytes of the encrypted string mattered, but -alternative hashing schemes (like MD5), higher level security schemes -(like C2), and implementations on non-UNIX platforms may produce -different strings. +the first eight bytes of the digest string mattered, but alternative +hashing schemes (like MD5), higher level security schemes (like C2), +and implementations on non-UNIX platforms may produce different +strings. When choosing a new salt create a random two character string whose characters come from the set C<[./0-9A-Za-z]> (like C accepts. Here's an example that makes sure that whoever runs this program knows -their own password: +their password: $pwd = (getpwuid($<))[1]; @@ -911,11 +949,9 @@ their own password: Of course, typing in your own password to whoever asks you for it is unwise. -The L function is unsuitable for encrypting large quantities +The L function is unsuitable for hashing large quantities of data, not least of all because you can't get the information -back. Look at the F and F directories -on your favorite CPAN mirror for a slew of potentially useful -modules. +back. Look at the L module for more robust algorithms. If using crypt() on a Unicode string (which I has characters with codepoints above 255), Perl tries to make sense @@ -1025,7 +1061,7 @@ defined values. For example, if you say "ab" =~ /a(.*)b/; The pattern match succeeds, and C<$1> is defined, despite the fact that it -matched "nothing". But it didn't really match nothing--rather, it +matched "nothing". It didn't really fail to match anything. Rather, it matched something that happened to be zero characters long. This is all very above-board and honest. When a function returns an undefined value, it's an admission that it couldn't give you an honest answer. So you @@ -1060,9 +1096,9 @@ from a Cd hash or array may not necessarily return anything. Deleting an array element effectively returns that position of the array to its initial, uninitialized state. Subsequently testing for the same -element with exists() will return false. Note that deleting array -elements in the middle of an array will not shift the index of the ones -after them down--use splice() for that. See L. +element with exists() will return false. Also, deleting array elements +in the middle of an array will not shift the index of the elements +after them down. Use splice() for that. See L. The following (inefficiently) deletes all the values of %HASH and @ARRAY: @@ -1145,7 +1181,7 @@ This is useful for propagating exceptions: If LIST is empty and C<$@> contains an object reference that has a C method, that method will be called with additional file and line number parameters. The return value replaces the value in -C<$@>. ie. as if C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> +C<$@>. i.e. as if C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> were called. If C<$@> is empty then the string C<"Died"> is used. @@ -1157,9 +1193,11 @@ maintain arbitrary state about the nature of the exception. Such a scheme is sometimes preferable to matching particular string values of $@ using regular expressions. Here's an example: + use Scalar::Util 'blessed'; + eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) }; if ($@) { - if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) { + if (blessed($@) && $@->isa("Some::Module::Exception")) { # handle Some::Module::Exception } else { @@ -1176,7 +1214,7 @@ does its deed, by setting the C<$SIG{__DIE__}> hook. The associated handler will be called with the error text and can change the error message, if it sees fit, by calling C again. See L for details on setting C<%SIG> entries, and -L<"eval BLOCK"> for some examples. Although this feature was meant +L<"eval BLOCK"> for some examples. Although this feature was to be run only right before your program was to exit, this is not currently the case--the C<$SIG{__DIE__}> hook is currently called even inside eval()ed blocks/strings! If one wants the hook to do @@ -1201,7 +1239,7 @@ See L for alternative strategies. =item do SUBROUTINE(LIST) -A deprecated form of subroutine call. See L. +This form of subroutine call is deprecated. See L. =item do EXPR @@ -1371,17 +1409,19 @@ there was an error. =item eval BLOCK +=item eval + In the first form, the return value of EXPR is parsed and executed as if it were a little Perl program. The value of the expression (which is itself determined within scalar context) is first parsed, and if there weren't any errors, executed in the lexical context of the current Perl program, so that any variable settings or subroutine and format definitions remain -afterwards. Note that the value is parsed every time the eval executes. +afterwards. Note that the value is parsed every time the C executes. If EXPR is omitted, evaluates C<$_>. This form is typically used to delay parsing and subsequent execution of the text of EXPR until run time. In the second form, the code within the BLOCK is parsed only once--at the -same time the code surrounding the eval itself was parsed--and executed +same time the code surrounding the C itself was parsed--and executed within the context of the current Perl program. This form is typically used to trap exceptions more efficiently than the first (see below), while also providing the benefit of checking the code within BLOCK at compile @@ -1393,8 +1433,9 @@ the BLOCK. In both forms, the value returned is the value of the last expression evaluated inside the mini-program; a return statement may be also used, just as with subroutines. The expression providing the return value is evaluated -in void, scalar, or list context, depending on the context of the eval itself. -See L for more on how the evaluation context can be determined. +in void, scalar, or list context, depending on the context of the C +itself. See L for more on how the evaluation context can be +determined. If there is a syntax error or runtime error, or a C statement is executed, an undefined value is returned by C, and C<$@> is set to the @@ -1427,9 +1468,9 @@ Examples: # a run-time error eval '$answer ='; # sets $@ -Due to the current arguably broken state of C<__DIE__> hooks, when using -the C form as an exception trap in libraries, you may wish not -to trigger any C<__DIE__> hooks that user code may have installed. +Using the C form as an exception trap in libraries does have some +issues. Due to the current arguably broken state of C<__DIE__> hooks, you +may wish not to trigger any C<__DIE__> hooks that user code may have installed. You can use the C construct for this purpose, as shown in this example: @@ -1619,6 +1660,8 @@ to exists() is an error. =item exit EXPR +=item exit + Evaluates EXPR and exits immediately with that value. Example: $ans = ; @@ -1715,8 +1758,8 @@ only entire files, not records. Two potentially non-obvious but traditional C semantics are that it waits indefinitely until the lock is granted, and that its locks B. Such discretionary locks are more flexible, but offer -fewer guarantees. This means that files locked with C may be -modified by programs that do not also use C. See L, +fewer guarantees. This means that programs that do not also use C +may modify files locked with C. See L, your port's specific documentation, or your system-specific local manpages for details. It's best to assume traditional behavior if you're writing portable programs. (But if you're not, you should as always feel perfectly @@ -1833,8 +1876,8 @@ too. It formats (see L) a list of values according to the contents of PICTURE, placing the output into the format output accumulator, C<$^A> (or C<$ACCUMULATOR> in English). Eventually, when a C is done, the contents of -C<$^A> are written to some filehandle, but you could also read C<$^A> -yourself and then set C<$^A> back to C<"">. Note that a format typically +C<$^A> are written to some filehandle. You could also read C<$^A> +and then set C<$^A> back to C<"">. Note that a format typically does one C per line of form, but the C function itself doesn't care how many newlines are embedded in the PICTURE. This means that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. @@ -1883,7 +1926,7 @@ L. =item getlogin -Implements the C library function of the same name, which on most +This implements the C library function of the same name, which on most systems returns the current login from F, if any. If null, use C. @@ -2040,8 +2083,8 @@ C, C, and C. Shadow password files are only supported if your vendor has implemented them in the intuitive fashion that calling the regular C library routines gets the shadow versions if you're running under privilege or if there exists -the shadow(3) functions as found in System V ( this includes Solaris -and Linux.) Those systems which implement a proprietary shadow password +the shadow(3) functions as found in System V (this includes Solaris +and Linux.) Those systems that implement a proprietary shadow password facility are unlikely to be supported. The $members value returned by I is a space separated list of @@ -2109,7 +2152,7 @@ The call returns a packed string representing the requested socket option, or C if there is an error (the error reason will be in $!). What exactly is in the packed string depends in the LEVEL and OPTNAME, consult your system documentation for details. A very common case however is that -the option is an integer, in which case the result will be an packed +the option is an integer, in which case the result will be a packed integer which you can decode using unpack with the C (or C) format. An example testing if Nagle's algorithm is turned on on a socket: @@ -2142,6 +2185,8 @@ C extension. See L for details. =item gmtime EXPR +=item gmtime + Converts a time as returned by the time function to an 8-element list with the time localized for the standard Greenwich time zone. Typically used as follows: @@ -2160,7 +2205,7 @@ is, $year is C<123> in year 2023. $wday is the day of the week, with the year, in the range C<0..364> (or C<0..365> in leap years.) Note that the $year element is I simply the last two digits of -the year. If you assume it is, then you create non-Y2K-compliant +the year. If you assume it is then you create non-Y2K-compliant programs--and you wouldn't want to do that, would you? The proper way to get a complete 4-digit year is simply: @@ -2185,6 +2230,8 @@ This scalar value is B locale dependent (see L), but is instead a Perl builtin. To get somewhat similar but locale dependent date strings, see the example in L. +See L for portability concerns. + =item goto LABEL =item goto EXPR @@ -2223,7 +2270,7 @@ After the C, not even C will be able to tell that this routine was called first. NAME needn't be the name of a subroutine; it can be a scalar variable -containing a code reference, or a block which evaluates to a code +containing a code reference, or a block that evaluates to a code reference. =item grep BLOCK LIST @@ -2254,7 +2301,7 @@ or another C) actually modifies the element in the original list. This is usually something to be avoided when writing clear code. If C<$_> is lexical in the scope where the C appears (because it has -been declared with C) then, in addition the be locally aliased to +been declared with C) then, in addition to being locally aliased to the list elements, C<$_> keeps being lexical inside the block; i.e. it can't be seen from the outside, avoiding any potential side-effects. @@ -2276,7 +2323,7 @@ integer overflow trigger a warning. Leading whitespace is not stripped, unlike oct(). To present something as hex, look into L, L, or L. -=item import +=item import LIST There is no builtin C function. It is just an ordinary method (subroutine) defined (or inherited) by modules that wish to export @@ -2293,7 +2340,7 @@ It returns the position of the first occurrence of SUBSTR in STR at or after POSITION. If POSITION is omitted, starts searching from the beginning of the string. The return value is based at C<0> (or whatever you've set the C<$[> variable to--but don't do that). If the substring -is not found, returns one less than the base, ordinarily C<-1>. +is not found, C returns one less than the base, ordinarily C<-1>. =item int EXPR @@ -2312,9 +2359,9 @@ functions will serve you better than will int(). Implements the ioctl(2) function. You'll probably first have to say - require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph + require "sys/ioctl.ph"; # probably in $Config{archlib}/ioctl.ph -to get the correct function definitions. If F doesn't +to get the correct function definitions. If F doesn't exist or doesn't have the correct definitions you'll have to roll your own, based on your C header files such as F<< >>. (There is a Perl script called B that comes with the Perl kit that @@ -2367,9 +2414,9 @@ Perl 5.8.1 the ordering is different even between different runs of Perl for security reasons (see L). -As a side effect, calling keys() resets the HASH's internal iterator, -see L. (In particular, calling keys() in void context resets -the iterator with no other overhead.) +As a side effect, calling keys() resets the HASH's internal iterator +(see L). In particular, calling keys() in void context resets +the iterator with no other overhead. Here is yet another way to print your environment: @@ -2582,6 +2629,8 @@ try for example: Note that the C<%a> and C<%b>, the short forms of the day of the week and the month of the year, may not necessarily be three characters wide. +See L for portability concerns. + =item lock THING This function places an advisory lock on a shared variable, or referenced @@ -2656,7 +2705,7 @@ most cases. See also L for an array composed of those items of the original list for which the BLOCK or EXPR evaluates to true. If C<$_> is lexical in the scope where the C appears (because it has -been declared with C) then, in addition the be locally aliased to +been declared with C) then, in addition to being locally aliased to the list elements, C<$_> keeps being lexical inside the block; i.e. it can't be seen from the outside, avoiding any potential side-effects. @@ -2687,10 +2736,13 @@ and you get list of anonymous hashes each with only 1 entry. =item mkdir FILENAME +=item mkdir + Creates the directory specified by FILENAME, with permissions specified by MASK (as modified by C). If it succeeds it returns true, otherwise it returns false and sets C<$!> (errno). -If omitted, MASK defaults to 0777. +If omitted, MASK defaults to 0777. If omitted, FILENAME defaults +to C<$_>. In general, it is better to create directories with permissive MASK, and let the user modify that with their C, than it is to supply @@ -2711,7 +2763,7 @@ Calls the System V IPC function msgctl(2). You'll probably have to say use IPC::SysV; first to get the correct constant definitions. If CMD is C, -then ARG must be a variable which will hold the returned C +then ARG must be a variable that will hold the returned C structure. Returns like C: the undefined value for error, C<"0 but true"> for zero, or the actual return value otherwise. See also L, C, and C documentation. @@ -2933,7 +2985,7 @@ modules that can help with that problem)) you should always check the return value from opening a file. The infrequent exception is when working with an unopened filehandle is actually what you want to do. -As a special case the 3 arg form with a read/write mode and the third +As a special case the 3-arg form with a read/write mode and the third argument being C: open(TMP, "+>", undef) or die ... @@ -2944,7 +2996,7 @@ to the temporary file first. You will need to seek() to do the reading. Since v5.8.0, perl has built using PerlIO by default. Unless you've -changed this (ie Configure -Uuseperlio), you can open file handles to +changed this (i.e. Configure -Uuseperlio), you can open file handles to "in memory" files held in Perl scalars via: open($fh, '>', \$variable) || .. @@ -3017,7 +3069,7 @@ duped (as L) and opened. You may use C<&> after C<< > >>, C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. The mode you specify should match the mode of the original filehandle. (Duping a filehandle does not take into account any existing contents -of IO buffers.) If you use the 3 arg form then you can pass either a +of IO buffers.) If you use the 3-arg form then you can pass either a number, the name of a filehandle or the normal "reference to a glob". Here is a script that saves, redirects, and restores C and @@ -3123,7 +3175,8 @@ be set for the newly opened file descriptor as determined by the value of $^F. See L. Closing any piped filehandle causes the parent process to wait for the -child to finish, and returns the status value in C<$?>. +child to finish, and returns the status value in C<$?> and +C<${^CHILD_ERROR_NATIVE}>. The filename passed to 2-argument (or 1-argument) form of open() will have leading and trailing whitespace deleted, and the normal @@ -3219,15 +3272,24 @@ See L and L for more about Unicode. =item our TYPE EXPR : ATTRS -An C declares the listed variables to be valid globals within -the enclosing block, file, or C. That is, it has the same -scoping rules as a "my" declaration, but does not create a local -variable. If more than one value is listed, the list must be placed -in parentheses. The C declaration has no semantic effect unless -"use strict vars" is in effect, in which case it lets you use the -declared global variable without qualifying it with a package name. -(But only within the lexical scope of the C declaration. In this -it differs from "use vars", which is package scoped.) +C associates a simple name with a package variable in the current +package for use within the current scope. When C is in +effect, C lets you use declared global variables without qualifying +them with package names, within the lexical scope of the C declaration. +In this way C differs from C, which is package scoped. + +Unlike C, which both allocates storage for a variable and associates +a simple name with that storage for use within the current scope, C +associates a simple name with a package variable in the current package, +for use within the current scope. In other words, C has the same +scoping rules as C, but does not necessarily create a +variable. + +If more than one value is listed, the list must be placed +in parentheses. + + our $foo; + our($bar, $baz); An C declaration declares a global variable that will be visible across its entire lexical scope, even across package boundaries. The @@ -3240,11 +3302,15 @@ behavior holds: $bar = 20; package Bar; - print $bar; # prints 20 + print $bar; # prints 20, as it refers to $Foo::bar -Multiple C declarations in the same lexical scope are allowed -if they are in different packages. If they happened to be in the same -package, Perl will emit warnings if you have asked for them. +Multiple C declarations with the same name in the same lexical +scope are allowed if they are in different packages. If they happen +to be in the same package, Perl will emit warnings if you have asked +for them, just like multiple C declarations. Unlike a second +C declaration, which will bind the name to a fresh variable, a +second C declaration in the same package, in the same scope, is +merely redundant. use warnings; package Foo; @@ -3255,7 +3321,8 @@ package, Perl will emit warnings if you have asked for them. our $bar = 30; # declares $Bar::bar for rest of lexical scope print $bar; # prints 30 - our $bar; # emits warning + our $bar; # emits warning but has no other effect + print $bar; # still prints 30 An C declaration may also have a list of attributes associated with it. @@ -3297,7 +3364,7 @@ Takes a LIST of values and converts it into a string using the rules given by the TEMPLATE. The resulting string is the concatenation of the converted values. Typically, each converted value looks like its machine-level representation. For example, on 32-bit machines -an integer may be represented by a sequence of 4 bytes which will be +an integer may be represented by a sequence of 4 bytes that will be converted to a sequence of 4 characters. The TEMPLATE is a sequence of characters that give the order and type @@ -3370,9 +3437,9 @@ of values, as follows: . Null fill or truncate to absolute position specified by value. ( Start of a ()-group. -Some letters in the TEMPLATE may optionally be followed by one or -more of these modifiers (the second column lists the letters for -which the modifier is valid): +One or more of the modifiers below may optionally follow some letters in the +TEMPLATE (the second column lists the letters for which the modifier is +valid): ! sSlLiI Forces native (short, long, int) sizes instead of fixed (16-/32-bit) sizes. @@ -3650,7 +3717,7 @@ binary representation (e.g. IEEE floating point format). Even if all platforms are using IEEE, there may be subtle differences. Being able to use C> or C> on floating point values can be very useful, but also very dangerous if you don't know exactly what you're doing. -It is definetely not a general way to portably store floating point +It is definitely not a general way to portably store floating point values. When using C> or C> on an C<()>-group, this will affect @@ -3735,7 +3802,7 @@ modifiers and a repeat count must follow immediately. =item * If TEMPLATE requires more arguments to pack() than actually given, pack() -assumes additional C<""> arguments. If TEMPLATE requires less arguments +assumes additional C<""> arguments. If TEMPLATE requires fewer arguments to pack() than actually given, extra arguments are ignored. =back @@ -3874,7 +3941,7 @@ array in subroutines, just like C. Returns the offset of where the last C search left off for the variable in question (C<$_> is used when the variable is not specified). Note that -0 is a valid match offset, while C indicates that the search position +0 is a valid match offset. C indicates that the search position is reset (usually due to match failure, but can also be because no match has yet been performed on the scalar). C directly accesses the location used by the regexp engine to store the offset, so assigning to C will change @@ -3910,8 +3977,9 @@ the corresponding right parenthesis to terminate the arguments to the print--interpose a C<+> or put parentheses around all the arguments. -Note that if you're storing FILEHANDLES in an array or other expression, -you will have to use a block returning its value instead: +Note that if you're storing FILEHANDLEs in an array, or if you're using +any other expression more complex than a scalar variable to retrieve it, +you will have to use a block returning the filehandle value instead: print { $files[$i] } "stuff\n"; print { $OK ? STDOUT : STDERR } "stuff\n"; @@ -4128,8 +4196,8 @@ in that case pretty much any characters can be read. The C command restarts the loop block without evaluating the conditional again. The C block, if any, is not executed. If the LABEL is omitted, the command refers to the innermost enclosing -loop. This command is normally used by programs that want to lie to -themselves about what was just input: +loop. Programs that want to lie to themselves about what was just input +normally use this command: # a simpleminded Pascal comment stripper # (warning: assumes no { or } in strings) @@ -4186,9 +4254,6 @@ name is returned instead. You can think of C as a C operator. unless (ref($r)) { print "r is not a reference at all.\n"; } - if (UNIVERSAL::isa($r, "HASH")) { # for subclassing - print "r is a reference to something that isa hash.\n"; - } See also L. @@ -4221,14 +4286,14 @@ Compare with L, which can do a similar check at compile time. Specifying VERSION as a literal of the form v5.6.1 should generally be avoided, because it leads to misleading error messages under earlier -versions of Perl which do not support this syntax. The equivalent numeric +versions of Perl that do not support this syntax. The equivalent numeric version should be used instead. require v5.6.1; # run time version check require 5.6.1; # ditto require 5.006_001; # ditto; preferred for backwards compatibility -Otherwise, demands that a library file be included if it hasn't already +Otherwise, C demands that a library file be included if it hasn't already been included. The file is included via the do-FILE mechanism, which is essentially just a variety of C. Has semantics similar to the following subroutine: @@ -4339,7 +4404,7 @@ or: ... } -If the hook is an object, it must provide an INC method, that will be +If the hook is an object, it must provide an INC method that will be called as above, the first parameter being the object itself. (Note that you must fully qualify the sub's name, as it is always forced into package C
.) Here is a typical code layout: @@ -4523,8 +4588,8 @@ cantankerous), then you may need something more like this: =item seekdir DIRHANDLE,POS Sets the current position for the C routine on DIRHANDLE. POS -must be a value returned by C. Has the same caveats about -possible directory compaction as the corresponding system library +must be a value returned by C. C also has the same caveats +about possible directory compaction as the corresponding system library routine. =item select FILEHANDLE @@ -4622,7 +4687,7 @@ Calls the System V IPC function C. You'll probably have to say use IPC::SysV; first to get the correct constant definitions. If CMD is IPC_STAT or -GETALL, then ARG must be a variable which will hold the returned +GETALL, then ARG must be a variable that will hold the returned semid_ds structure or semaphore value array. Returns like C: the undefined value for error, "C<0 but true>" for zero, or the actual return value otherwise. The ARG must consist of a vector of native @@ -4642,8 +4707,8 @@ documentation. Calls the System V IPC function semop to perform semaphore operations such as signalling and waiting. OPSTRING must be a packed array of semop structures. Each semop structure can be generated with -C. The number of semaphore -operations is implied by the length of OPSTRING. Returns true if +C. The length of OPSTRING +implies the number of semaphore operations. Returns true if successful, or false if there is an error. As an example, the following code waits on semaphore $semnum of semaphore id $semid: @@ -4703,9 +4768,9 @@ Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down. If there are no elements in the array, returns the undefined value. If ARRAY is omitted, shifts the C<@_> array within the lexical scope of subroutines and formats, and the -C<@ARGV> array at file scopes or within the lexical scopes established by -the C, C, C, C, and C -constructs. +C<@ARGV> array outside of a subroutine and also within the lexical scopes +established by the C, C, C, C +and C constructs. See also C, C, and C. C and C do the same thing to the left end of an array that C and C do to the @@ -4718,7 +4783,7 @@ Calls the System V IPC function shmctl. You'll probably have to say use IPC::SysV; first to get the correct constant definitions. If CMD is C, -then ARG must be a variable which will hold the returned C +then ARG must be a variable that will hold the returned C structure. Returns like ioctl: the undefined value for error, "C<0> but true" for zero, or the actual return value otherwise. See also L and C documentation. @@ -4856,7 +4921,7 @@ in the latter case, it is usually counter-productive to declare $a and $b as lexicals. In either case, the subroutine may not be recursive. The values to be -compared are always passed by reference, so don't modify them. +compared are always passed by reference and should not be modified. You also cannot exit out of the sort block or subroutine using any of the loop control operators described in L or with C. @@ -4870,11 +4935,11 @@ preserves the input order of elements that compare equal. Although quicksort's run time is O(NlogN) when averaged over all arrays of length N, the time can be O(N**2), I behavior, for some inputs.) In 5.7, the quicksort implementation was replaced with -a stable mergesort algorithm whose worst case behavior is O(NlogN). +a stable mergesort algorithm whose worst-case behavior is O(NlogN). But benchmarks indicated that for some inputs, on some platforms, the original quicksort was faster. 5.8 has a sort pragma for limited control of the sort. Its rather blunt control of the -underlying algorithm may not persist into future perls, but the +underlying algorithm may not persist into future Perls, but the ability to characterize the input or output in implementation independent ways quite probably will. See L. @@ -5074,14 +5139,19 @@ characters at each point it matches that way. For example: produces the output 'h:i:t:h:e:r:e'. -Using the empty pattern C specifically matches the null string, and is -not be confused with the use of C to mean "the last successful pattern -match". +As a special case for C, using the empty pattern C specifically +matches only the null string, and is not be confused with the regular use +of C to mean "the last successful pattern match". So, for C, +the following: -Empty leading (or trailing) fields are produced when there are positive width -matches at the beginning (or end) of the string; a zero-width match at the -beginning (or end) of the string does not produce an empty field. For -example: + print join(':', split(//, 'hi there')); + +produces the output 'h:i: :t:h:e:r:e'. + +Empty leading (or trailing) fields are produced when there are positive +width matches at the beginning (or end) of the string; a zero-width match +at the beginning (or end) of the string does not produce an empty field. +For example: print join(':', split(/(?=\w)/, 'hi there!')); @@ -5218,7 +5288,7 @@ In order, these are: An explicit format parameter index, such as C<2$>. By default sprintf will format the next unused argument in the list, but this allows you -to take the arguments out of order. Eg: +to take the arguments out of order, e.g.: printf '%2$d %1$d', 12, 34; # prints "34 12" printf '%3$d %d %1$d', 1, 2, 3; # prints "3 1 1" @@ -5259,7 +5329,7 @@ use to separate the numbers: printf "bits are %0*v8b\n", " ", $bits; # random bitstring You can also explicitly specify the argument number to use for -the join string using eg C<*2$v>: +the join string using e.g. C<*2$v>: printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":"; # 3 IPv6 addresses @@ -5268,7 +5338,7 @@ the join string using eg C<*2$v>: Arguments are usually formatted to be only as wide as required to display the given value. You can override the width by putting a number here, or get the width from the next argument (with C<*>) -or from a specified argument (with eg C<*2$>): +or from a specified argument (with e.g. C<*2$>): printf '<%s>', "a"; # prints "" printf '<%6s>', "a"; # prints "< a>" @@ -5284,7 +5354,7 @@ effect as the C<-> flag: left-justification. You can specify a precision (for numeric conversions) or a maximum width (for string conversions) by specifying a C<.> followed by a number. For floating point formats, with the exception of 'g' and 'G', this specifies -the number of decimal places to show (the default being 6), eg: +the number of decimal places to show (the default being 6), e.g.: # these examples are subject to system-specific variation printf '<%f>', 1; # prints "<1.000000>" @@ -5294,7 +5364,7 @@ the number of decimal places to show (the default being 6), eg: printf '<%.1e>', 10; # prints "<1.0e+01>" For 'g' and 'G', this specifies the maximum number of digits to show, -including prior to the decimal point as well as after it, eg: +including prior to the decimal point as well as after it, e.g.: # these examples are subject to system-specific variation printf '<%g>', 1; # prints "<1>" @@ -5325,7 +5395,7 @@ You can also get the precision from the next argument using C<.*>: You cannot currently get the precision from a specified number, but it is intended that this will be possible in the future using -eg C<.*2$>: +e.g. C<.*2$>: printf '<%.*2$x>', 1, 6; # INVALID, but in future will print "<000001>" @@ -5468,8 +5538,8 @@ current C