X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlsyn.pod;h=257938ce5310434b5062b93cdbf2fd2e6d0ba6a3;hb=b30f304ae36b3931349d7d5816f5a5646afe5397;hp=d5fe7fbb5a16f03ec1ea0b2a05d7d20d555f195f;hpb=6ec4bd10d4541458cd84a1df72dd948b519e53e9;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod index d5fe7fb..257938c 100644 --- a/pod/perlsyn.pod +++ b/pod/perlsyn.pod @@ -4,23 +4,27 @@ perlsyn - Perl syntax =head1 DESCRIPTION -A Perl script consists of a sequence of declarations and statements. -The sequence of statements is executed just once, unlike in B -and B scripts, where the sequence of statements is executed -for each input line. While this means that you must explicitly -loop over the lines of your input file (or files), it also means -you have much more control over which files and which lines you look at. -(Actually, I'm lying--it is possible to do an implicit loop with -either the B<-n> or B<-p> switch. It's just not the mandatory -default like it is in B and B.) - -Perl is, for the most part, a free-form language. (The only exception -to this is format declarations, for obvious reasons.) Text from a -C<"#"> character until the end of the line is a comment, and is -ignored. If you attempt to use C C-style comments, it will be -interpreted either as division or pattern matching, depending on the -context, and C++ C comments just look like a null regular -expression or defined-or operator, so don't do that. +A Perl program consists of a sequence of declarations and statements +which run from the top to the bottom. Loops, subroutines and other +control structures allow you to jump around within the code. + +Perl is a B language, you can format and indent it however +you like. Whitespace mostly serves to separate tokens, unlike +languages like Python where it is an important part of the syntax. + +Many of Perl's syntactic elements are B. Rather than +requiring you to put parentheses around every function call and +declare every variable, you can often leave such explicit elements off +and Perl will figure out what you meant. This is known as B, abbreviated B. It allows programmers to be B and to +code in a style with which they are comfortable. + +Perl B and concepts from many languages: awk, sed, C, +Bourne Shell, Smalltalk, Lisp and even English. Other +languages have borrowed syntax from Perl, particularly its regular +expression extensions. So if you have programmed in another language +you will see familiar pieces in Perl. They often work the same, but +see L for information about how they differ. =head2 Declarations @@ -79,6 +83,12 @@ like an ordinary statement, and is elaborated within the sequence of statements as if it were an ordinary statement. That means it actually has both compile-time and run-time effects. +=head2 Comments + +Text from a C<"#"> character until the end of the line is a comment, +and is ignored. Exceptions include C<"#"> inside a string or regular +expression. + =head2 Simple Statements The only kind of simple statement is an expression evaluated for its @@ -636,13 +646,13 @@ with C). The syntax for this mechanism is the same as for most C preprocessors: it matches the regular expression # example: '# line 42 "new_filename.plx"' - /^# \s* + /^\# \s* line \s+ (\d+) \s* - (?:\s"([^"]+)")? \s* + (?:\s("?)([^"]+)\2)? \s* $/x -with C<$1> being the line number for the next line, and C<$2> being -the optional filename (specified within quotes). +with C<$1> being the line number for the next line, and C<$3> being +the optional filename (specified with or without quotes). There is a fairly obvious gotcha included with the line directive: Debuggers and profilers will only show the last source line to appear