=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.27 $, $Date: 1998/07/05 15:07:20 $)
+perlfaq3 - Programming Tools ($Revision: 1.28 $, $Date: 1998/07/16 22:08:49 $)
=head1 DESCRIPTION
=head2 How can I use Perl interactively?
The typical approach uses the Perl debugger, described in the
-perldebug(1) man page, on an "empty" program, like this:
+perldebug(1) man page, on an ``empty'' program, like this:
perl -de 42
Now just type in any legal Perl code, and it will be immediately
evaluated. You can also examine the symbol table, get stack
backtraces, check variable values, set breakpoints, and other
-operations typically found in symbolic debuggers
+operations typically found in symbolic debuggers.
=head2 Is there a Perl shell?
=head2 How do I debug my Perl programs?
-Have you used C<-w>?
+Have you used C<-w>? It enables warnings for dubious practices.
-Have you tried C<use strict>?
+Have you tried C<use strict>? It prevents you from using symbolic
+references, makes you predeclare any subroutines that you call as bare
+words, and (probably most importantly) forces you to predeclare your
+variables with C<my> or C<use vars>.
-Did you check the returns of each and every system call?
+Did you check the returns of each and every system call? The operating
+system (and thus Perl) tells you whether they worked or not, and if not
+why.
-Did you read L<perltrap>?
+ open(FH, "> /etc/cantwrite")
+ or die "Couldn't write to /etc/cantwrite: $!\n";
-Have you tried the Perl debugger, described in L<perldebug>?
+Did you read L<perltrap>? It's full of gotchas for old and new Perl
+programmers, and even has sections for those of you who are upgrading
+from languages like I<awk> and I<C>.
+
+Have you tried the Perl debugger, described in L<perldebug>? You can
+step through your program and see what it's doing and thus work out
+why what it's doing isn't what it should be doing.
=head2 How do I profile my Perl programs?
specific portions of your code, while Devel::DProf gives detailed
breakdowns of where your code spends its time.
+Here's a sample use of Benchmark:
+
+ use Benchmark;
+
+ @junk = `cat /etc/motd`;
+ $count = 10_000;
+
+ timethese($count, {
+ 'map' => sub { my @a = @junk;
+ map { s/a/b/ } @a;
+ return @a
+ },
+ 'for' => sub { my @a = @junk;
+ local $_;
+ for (@a) { s/a/b/ };
+ return @a },
+ });
+
+This is what it prints (on one machine--your results will be dependent
+on your hardware, operating system, and the load on your machine):
+
+ Benchmark: timing 10000 iterations of for, map...
+ for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
+ map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
+
=head2 How do I cross-reference my Perl programs?
The B::Xref module, shipped with the new, alpha-release Perl compiler
=head2 Is there a pretty-printer (formatter) for Perl?
-There is no program that will reformat Perl as much as indent(1) will
-do for C. The complex feedback between the scanner and the parser
-(this feedback is what confuses the vgrind and emacs programs) makes it
+There is no program that will reformat Perl as much as indent(1) does
+for C. The complex feedback between the scanner and the parser (this
+feedback is what confuses the vgrind and emacs programs) makes it
challenging at best to write a stand-alone Perl parser.
Of course, if you simply follow the guidelines in L<perlstyle>, you
-shouldn't need to reformat.
-
-Your editor can and should help you with source formatting. The
-perl-mode for emacs can provide a remarkable amount of help with most
-(but not all) code, and even less programmable editors can provide
-significant assistance.
-
-If you are used to using vgrind program for printing out nice code to
-a laser printer, you can take a stab at this using
+shouldn't need to reformat. The habit of formatting your code as you
+write it will help prevent bugs. Your editor can and should help you
+with this. The perl-mode for emacs can provide a remarkable amount of
+help with most (but not all) code, and even less programmable editors
+can provide significant assistance.
+
+If you are used to using I<vgrind> program for printing out nice code
+to a laser printer, you can take a stab at this using
http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
results are not particularly satisfying for sophisticated code.
which contains a cperl-mode that color-codes keywords, provides
context-sensitive help, and other nifty things.
-Note that the perl-mode of emacs will have fits with "main'foo"
+Note that the perl-mode of emacs will have fits with C<"main'foo">
(single quote), and mess up the indentation and hilighting. You
-should be using "main::foo", anyway.
+should be using C<"main::foo"> in new Perl code anyway, so this
+shouldn't be an issue.
=head2 How can I use curses with Perl?
to the Athena Widget set. Both are available from CPAN. See the
directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
+Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at
+http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference
+Guide available at
+http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
+online manpages at
+http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html .
+
=head2 How can I generate simple menus without using CGI or Tk?
The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
=head2 How can I make my Perl program run faster?
-The best way to do this is to come up with a better algorithm.
-This can often make a dramatic difference. Chapter 8 in the Camel
-has some efficiency tips in it you might want to look at.
+The best way to do this is to come up with a better algorithm. This
+can often make a dramatic difference. Chapter 8 in the Camel has some
+efficiency tips in it you might want to look at. Jon Bentley's book
+``Programming Pearls'' (that's not a misspelling!) has some good tips
+on optimization, too. Advice on benchmarking boils down to: benchmark
+and profile to make sure you're optimizing the right part, look for
+better algorithms instead of microtuning your code, and when all else
+fails consider just buying faster hardware.
-Other approaches include autoloading seldom-used Perl code. See the
+A different approach is to autoload seldom-used Perl code. See the
AutoSplit and AutoLoader modules in the standard distribution for
that. Or you could locate the bottleneck and think about writing just
that part in C, the way we used to take bottlenecks in C code and
produce byte code (saving compilation time) or compile into C, which
will certainly save compilation time and sometimes a small amount (but
not much) execution time. See the question about compiling your Perl
-programs.
+programs for more on the compiler--the wins aren't as obvious as you'd
+hope.
-If you're currently linking your perl executable to a shared libc.so,
+If you're currently linking your perl executable to a shared I<libc.so>,
you can often gain a 10-25% performance benefit by rebuilding it to
link with a static libc.a instead. This will make a bigger perl
executable, but your Perl programs (and programmers) may thank you for
Unsubstantiated reports allege that Perl interpreters that use sfio
outperform those that don't (for IO intensive applications). To try
this, see the F<INSTALL> file in the source distribution, especially
-the "Selecting File IO mechanisms" section.
+the ``Selecting File IO mechanisms'' section.
The undump program was an old attempt to speed up your Perl program
by storing the already-compiled form to disk. This is no longer
However, judicious use of my() on your variables will help make sure
that they go out of scope so that Perl can free up their storage for
-use in other parts of your program. (NB: my() variables also execute
-about 10% faster than globals.) A global variable, of course, never
+use in other parts of your program. A global variable, of course, never
goes out of scope, so you can't get its space automatically reclaimed,
although undef()ing and/or delete()ing it will achieve the same effect.
In general, memory allocation and de-allocation isn't something you can
memory, this can be a killer. Compiling into C B<isn't going to help
you> because the process start-up overhead is where the bottleneck is.
-There are at least two popular ways to avoid this overhead. One
-solution involves running the Apache HTTP server (available from
+There are two popular ways to avoid this overhead. One solution
+involves running the Apache HTTP server (available from
http://www.apache.org/) with either of the mod_perl or mod_fastcgi
-plugin modules. With mod_perl and the Apache::* modules (from CPAN),
-httpd will run with an embedded Perl interpreter which pre-compiles
-your script and then executes it within the same address space without
-forking. The Apache extension also gives Perl access to the internal
-server API, so modules written in Perl can do just about anything a
-module written in C can. With the FCGI module (from CPAN), a Perl
-executable compiled with sfio (see the F<INSTALL> file in the
-distribution) and the mod_fastcgi module (available from
-http://www.fastcgi.com/) each of your perl scripts becomes a permanent
-CGI daemon process.
+plugin modules.
+
+With mod_perl and the Apache::Registry module (distributed with
+mod_perl), httpd will run with an embedded Perl interpreter which
+pre-compiles your script and then executes it within the same address
+space without forking. The Apache extension also gives Perl access to
+the internal server API, so modules written in Perl can do just about
+anything a module written in C can. For more on mod_perl, see
+http://perl.apache.org/
+
+With the FCGI module (from CPAN), a Perl executable compiled with sfio
+(see the F<INSTALL> file in the distribution) and the mod_fastcgi
+module (available from http://www.fastcgi.com/) each of your perl
+scripts becomes a permanent CGI daemon process.
Both of these solutions can have far-reaching effects on your system
and on the way you write your CGI scripts, so investigate them with
care.
-See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/.
+See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
-A non-free, commerical product, 'The Velocity Engine for Perl',
+A non-free, commerical product, ``The Velocity Engine for Perl'',
(http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might
also be worth looking at. It will allow you to increase the performance
-of your perl scripts, upto 25 times faster than normal cgi perl by
+of your perl scripts, upto 25 times faster than normal CGI perl by
running in persistent perl mode, or 4 to 5 times faster without any
-modification to your existing cgi scripts. Fully functional evaluation
+modification to your existing CGI scripts. Fully functional evaluation
copies are available from the web site.
=head2 How can I hide the source for my Perl program?
Delete it. :-) Seriously, there are a number of (mostly
-unsatisfactory) solutions with varying levels of "security".
+unsatisfactory) solutions with varying levels of ``security''.
First of all, however, you I<can't> take away read permission, because
the source code has to be readable in order to be compiled and
interpreted. (That doesn't mean that a CGI script's source is
-readable by people on the web, though.) So you have to leave the
-permissions at the socially friendly 0755 level.
+readable by people on the web, though, only by people with access to
+the filesystem) So you have to leave the permissions at the socially
+friendly 0755 level.
Some people regard this as a security problem. If your program does
insecure things, and relies on people not knowing how to exploit those
source. Security through obscurity, the name for hiding your bugs
instead of fixing them, is little security indeed.
-You can try using encryption via source filters (Filter::* from CPAN).
-But crackers might be able to decrypt it. You can try using the byte
+You can try using encryption via source filters (Filter::* from CPAN),
+but crackers might be able to decrypt it. You can try using the byte
code compiler and interpreter described below, but crackers might be
able to de-compile it. You can try using the native-code compiler
described below, but crackers might be able to disassemble it. These
If you're concerned about people profiting from your code, then the
bottom line is that nothing but a restrictive licence will give you
legal security. License your software and pepper it with threatening
-statements like "This is unpublished proprietary software of XYZ Corp.
+statements like ``This is unpublished proprietary software of XYZ Corp.
Your access to it does not give you permission to use it blah blah
-blah." We are not lawyers, of course, so you should see a lawyer if
+blah.'' We are not lawyers, of course, so you should see a lawyer if
you want to be sure your licence's wording will stand up in court.
=head2 How can I compile my Perl program into byte code or C?
Malcolm Beattie has written a multifunction backend compiler,
available from CPAN, that can do both these things. It is as of
-Feb-1997 in late alpha release, which means it's fun to play with if
+Jul-1998 in late alpha release, which means it's fun to play with if
you're a programmer but not really for people looking for turn-key
solutions.
-I<Please> understand that merely compiling into C does not in and of
-itself guarantee that your code will run very much faster. That's
-because except for lucky cases where a lot of native type inferencing
-is possible, the normal Perl run time system is still present and thus
-will still take just as long to run and be just as big. Most programs
-save little more than compilation time, leaving execution no more than
-10-30% faster. A few rare programs actually benefit significantly
-(like several times faster), but this takes some tweaking of your
-code.
+Merely compiling into C does not in and of itself guarantee that your
+code will run very much faster. That's because except for lucky cases
+where a lot of native type inferencing is possible, the normal Perl
+run time system is still present and so your program will take just as
+long to run and be just as big. Most programs save little more than
+compilation time, leaving execution no more than 10-30% faster. A few
+rare programs actually benefit significantly (like several times
+faster), but this takes some tweaking of your code.
The 5.005 release of Perl itself, whose main goal is merging the various
non-Unix ports back into the one Perl source, will also have preliminary
(strictly beta) support for Malcolm's compiler and his light-weight
-processes (sometimes called "threads").
+processes (sometimes called ``threads'').
You'll probably be astonished to learn that the current version of the
compiler generates a compiled form of your script whose executable is
just as big as the original perl executable, and then some. That's
because as currently written, all programs are prepared for a full
eval() statement. You can tremendously reduce this cost by building a
-shared libperl.so library and linking against that. See the
+shared I<libperl.so> library and linking against that. See the
F<INSTALL> podfile in the perl source distribution for details. If
you link your main perl binary with this, it will make it miniscule.
-For example, on one author's system, /usr/bin/perl is only 11k in
+For example, on one author's system, F</usr/bin/perl> is only 11k in
size!
In general, the compiler will do nothing to make a Perl program smaller,
you use a shared I<libperl.so>), you'll probably want a complete
Perl install anywayt.
-=head2 How can I get '#!perl' to work on [MS-DOS,NT,...]?
+=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
For OS/2 just use
batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the
F<INSTALL> file in the source distribution for more information).
-The Win95/NT installation, when using the Activeware port of Perl,
-will modify the Registry to associate the .pl extension with the perl
-interpreter. If you install another port, or (eventually) build your
-own Win95/NT Perl using WinGCC, then you'll have to modify the
-Registry yourself.
+The Win95/NT installation, when using the ActiveState port of Perl,
+will modify the Registry to associate the C<.pl> extension with the
+perl interpreter. If you install another port (Gurusaramy Sarathy's
+is the recommended Win95/NT port), or (eventually) build your own
+Win95/NT Perl using WinGCC, then you'll have to modify the Registry
+yourself.
Macintosh perl scripts will have the the appropriate Creator and
Type, so that double-clicking them will invoke the perl application.
# VMS
perl -e "print ""Hello world\n"""
-The problem is that none of this is reliable: it depends on the command
-interpreter. Under Unix, the first two often work. Under DOS, it's
-entirely possible neither works. If 4DOS was the command shell, I'd
-probably have better luck like this:
+The problem is that none of this is reliable: it depends on the
+command interpreter. Under Unix, the first two often work. Under DOS,
+it's entirely possible neither works. If 4DOS was the command shell,
+you'd probably have better luck like this:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
quoting variants, except that it makes free use of the Mac's non-ASCII
characters as control characters.
-I'm afraid that there is no general solution to all of this. It is a
-mess, pure and simple.
+There is no general solution to all of this. It is a mess, pure and
+simple. Sucks to be away from Unix, huh? :-)
[Some of this answer was contributed by Kenneth Albanowski.]
For modules, get the CGI or LWP modules from CPAN. For textbooks,
see the two especially dedicated to web stuff in the question on
-books. For problems and questions related to the web, like "Why
-do I get 500 Errors" or "Why doesn't it run from the browser right
-when it runs fine on the command line", see these sources:
+books. For problems and questions related to the web, like ``Why
+do I get 500 Errors'' or ``Why doesn't it run from the browser right
+when it runs fine on the command line'', see these sources:
WWW Security FAQ
http://www.w3.org/Security/Faq/
=head1 NAME
-perlfaq4 - Data Manipulation ($Revision: 1.24 $, $Date: 1998/07/05 15:07:20 $)
+perlfaq4 - Data Manipulation ($Revision: 1.25 $, $Date: 1998/07/16 22:49:55 $)
=head1 DESCRIPTION
number of bits to store an infinite number of, um, numbers.
Internally, your computer represents floating-point numbers in binary.
-Floating-point numbers read in from a file, or appearing as literals
-in your program, are converted from their decimal floating-point
+Floating-point numbers read in from a file or appearing as literals
+in your program are converted from their decimal floating-point
representation (eg, 19.95) to the internal binary representation.
However, 19.95 can't be precisely represented as a binary
=head2 Does perl have a round function? What about ceil() and floor()? Trig functions?
-Remember that int() merely truncates toward 0. For rounding to a certain
-number of digits, sprintf() or printf() is usually the easiest route.
+Remember that int() merely truncates toward 0. For rounding to a
+certain number of digits, sprintf() or printf() is usually the easiest
+route.
+
+ printf("%.3f", 3.1415926535); # prints 3.142
The POSIX module (part of the standard perl distribution) implements
ceil(), floor(), and a number of other mathematical and trigonometric
functions.
+ use POSIX;
+ $ceil = ceil(3.5); # 4
+ $floor = floor(3.5); # 3
+
In 5.000 to 5.003 Perls, trigonometry was done in the Math::Complex
module. With 5.004, the Math::Trig module (part of the standard perl
distribution) implements the trigonometric functions. Internally it
=head2 How do I convert bits into ints?
-To turn a string of 1s and 0s like '10110110' into a scalar containing
+To turn a string of 1s and 0s like C<10110110> into a scalar containing
its binary value, use the pack() function (documented in
L<perlfunc/"pack">):
=head2 Why aren't my random numbers random?
-John von Neumann said, ``Anyone who attempts to generate random numbers by
-deterministic means is, of course, living in a state of sin.''
-
The short explanation is that you're getting pseudorandom numbers, not
-random ones, because that's how these things work. A longer explanation
-is available on http://www.perl.com/CPAN/doc/FMTEYEWTK/random, courtesy
-of Tom Phoenix.
-
-You should also check out the Math::TrulyRandom module from CPAN.
+random ones, because computers are good at being predictable and bad
+at being random (despite appearances caused by bugs in your programs
+:-). A longer explanation is available on
+http://www.perl.com/CPAN/doc/FMTEYEWTK/random, courtesy of Tom
+Phoenix. John von Neumann said, ``Anyone who attempts to generate
+random numbers by deterministic means is, of course, living in a state
+of sin.''
+
+You should also check out the Math::TrulyRandom module from CPAN. It
+uses the imperfections in your system's timer to generate random
+numbers, but this takes quite a while. If you want a better
+pseudorandom generator than comes with your operating system, look at
+``Numerical Recipes in C'' at http://nr.harvard.edu/nr/bookc.html .
=head1 Data: Dates
$week_of_year = int($day_of_year / 7);
-Of course, this believes that weeks start at zero.
+Of course, this believes that weeks start at zero. The Date::Calc
+module from CPAN has a lot of date calculation functions, including
+day of the year, week of the year, and so on.
-=head2 How can I compare two date strings?
+=head2 How can I compare two dates and find the difference?
-Use the Date::Manip or Date::DateCalc modules from CPAN.
+If you're storing your dates as epoch seconds then simply subtract one
+from the other. If you've got a structured date (distinct year, day,
+month, hour, minute, seconds values) then use one of the Date::Manip
+and Date::Calc modules from CPAN.
=head2 How can I take a string and turn it into epoch seconds?
If it's a regular enough string that it always has the same format,
-you can split it up and pass the parts to timelocal in the standard
-Time::Local module. Otherwise, you should look into one of the
-Date modules from CPAN.
+you can split it up and pass the parts to C<timelocal> in the standard
+Time::Local module. Otherwise, you should look into the Date::Calc
+and Date::Manip modules from CPAN.
=head2 How can I find the Julian Day?
-Neither Date::Manip nor Date::DateCalc deal with Julian days.
-Instead, there is an example of Julian date calculation in
-http://www.perl.com/CPAN/authors/David_Muir_Sharnoff/modules/Time/JulianDay.pm.gz,
-which should help.
+Neither Date::Manip nor Date::Calc deal with Julian days. Instead,
+there is an example of Julian date calculation that should help you in
+http://www.perl.com/CPAN/authors/David_Muir_Sharnoff/modules/Time/JulianDay.pm.gz
+.
=head2 Does Perl have a year 2000 problem? Is Perl Y2K compliant?
-Perl is just as Y2K compliant as your pencil--no more, and no less.
-The date and time functions supplied with perl (gmtime and localtime)
-supply adequate information to determine the year well beyond 2000
-(2038 is when trouble strikes for 32-bit machines). The year returned
-by these functions when used in an array context is the year minus 1900.
-For years between 1910 and 1999 this I<happens> to be a 2-digit decimal
-number. To avoid the year 2000 problem simply do not treat the year as
-a 2-digit number. It isn't.
+Short answer: No, Perl does not have a Year 2000 problem. Yes, Perl
+is Y2K compliant.
+
+Long answer: Perl is just as Y2K compliant as your pencil--no more,
+and no less. The date and time functions supplied with perl (gmtime
+and localtime) supply adequate information to determine the year well
+beyond 2000 (2038 is when trouble strikes for 32-bit machines). The
+year returned by these functions when used in an array context is the
+year minus 1900. For years between 1910 and 1999 this I<happens> to
+be a 2-digit decimal number. To avoid the year 2000 problem simply do
+not treat the year as a 2-digit number. It isn't.
When gmtime() and localtime() are used in scalar context they return
a timestamp string that contains a fully-expanded year. For example,
=head2 How do I unescape a string?
-It depends just what you mean by "escape". URL escapes are dealt with
-in L<perlfaq9>. Shell escapes with the backslash (\)
+It depends just what you mean by ``escape''. URL escapes are dealt
+with in L<perlfaq9>. Shell escapes with the backslash (C<\>)
character are removed with:
s/\\(.)/$1/g;
-Note that this won't expand \n or \t or any other special escapes.
+This won't expand C<"\n"> or C<"\t"> or any other special escapes.
=head2 How do I remove consecutive pairs of characters?
-To turn "abbcccd" into "abccd":
+To turn C<"abbcccd"> into C<"abccd">:
s/(.)\1/$1/g;
print "That yields ${\($n + 5)} widgets\n";
-See also "How can I expand variables in text strings?" in this section
-of the FAQ.
+Version 5.004 of Perl had a bug that gave list context to the
+expression in C<${...}>, but this is fixed in version 5.005.
+
+See also ``How can I expand variables in text strings?'' in this
+section of the FAQ.
=head2 How do I find matching/nesting anything?
-This isn't something that can be tackled in one regular expression, no
-matter how complicated. To find something between two single characters,
-a pattern like C</x([^x]*)x/> will get the intervening bits in $1. For
-multiple ones, then something more like C</alpha(.*?)omega/> would
-be needed. But none of these deals with nested patterns, nor can they.
-For that you'll have to write a parser.
+This isn't something that can be done in one regular expression, no
+matter how complicated. To find something between two single
+characters, a pattern like C</x([^x]*)x/> will get the intervening
+bits in $1. For multiple ones, then something more like
+C</alpha(.*?)omega/> would be needed. But none of these deals with
+nested patterns, nor can they. For that you'll have to write a
+parser.
+
+If you are serious about writing a parser, there are a number of
+modules or oddities that will make your life a lot easier. There is
+the CPAN module Parse::RecDescent, the standard module Text::Balanced,
+the byacc program, and Mark-Jason Dominus's excellent I<py> tool at
+http://www.plover.com/~mjd/perl/py/ .
-One destructive, inside-out approach that you might try is to pull
-out the smallest nesting parts one at a time:
+One simple destructive, inside-out approach that you might try is to
+pull out the smallest nesting parts one at a time:
while (s//BEGIN((?:(?!BEGIN)(?!END).)*)END/gs) {
# do something with $1
use Text::Wrap;
print wrap("\t", ' ', @paragraphs);
-The paragraphs you give to Text::Wrap may not contain embedded
+The paragraphs you give to Text::Wrap should not contain embedded
newlines. Text::Wrap doesn't justify the lines (flush-right).
=head2 How can I access/change the first N letters of a string?
There are many ways. If you just want to grab a copy, use
-substr:
+substr():
$first_byte = substr($a, 0, 1);
substr($a, 0, 3) = "Tom";
-Although those with a regexp kind of thought process will likely prefer
+Although those with a pattern matching kind of thought process will
+likely prefer:
$a =~ s/^.../Tom/;
=head2 How do I change the Nth occurrence of something?
-You have to keep track. For example, let's say you want
-to change the fifth occurrence of "whoever" or "whomever"
-into "whosoever" or "whomsoever", case insensitively.
+You have to keep track of N yourself. For example, let's say you want
+to change the fifth occurrence of C<"whoever"> or C<"whomever"> into
+C<"whosoever"> or C<"whomsoever">, case insensitively.
$count = 0;
s{((whom?)ever)}{
}
}
-That prints out: "The third fish is a red one." You can also use a
+That prints out: C<"The third fish is a red one."> You can also use a
repetition count and repeated pattern like this:
/(?:\w+\s+fish\s+){2}(\w+)\s+fish/i;
This has the strange effect of turning "C<don't do it>" into "C<Don'T
Do It>". Sometimes you might want this, instead (Suggested by Brian
-Foy E<lt>comdog@computerdog.comE<gt>):
+Foy):
$string =~ s/ (
(^\w) #at the beginning of the line
You can (and probably should) enable locale awareness of those
characters by placing a C<use locale> pragma in your program.
-See L<perllocale> for endless details.
+See L<perllocale> for endless details on locales.
=head2 How can I split a [character] delimited string except when inside
[character]? (Comma-separated files)
s/\s+$//;
}
-This idiom takes advantage of the for(each) loop's aliasing
+This idiom takes advantage of the C<for(each)> loop's aliasing
behavior to factor out common code. You can do this
on several strings at once, or arrays, or even the
values of a hash if you use a slide:
);
$text =~ s/\$(\w+)/$user_defs{$1}/g;
-See also "How do I expand function calls in a string?" in this section
+See also ``How do I expand function calls in a string?'' in this section
of the FAQ.
=head2 What's wrong with always quoting "$vars"?
projects / p5sagit/p5-mst-13.2.git / commitdiff