Special Edition Using PERL 5 for Web Programming by David Harlan

Show description

In this case, if the left side of an expression is false, the expression as a whole is false, so Perl does not evaluate the right side. The && operator can, therefore, be used to produce the same kind of effect as the || trick, but with the opposite sense, as in the following example: $value > 10 && print "OK, value is high enough \n"; As is true of most Perl constructs, the real power of these tricks comes when you apply a little creative thinking. Remember that the left and right sides of these expressions can be any Perl expressions; think of them as being conjunctions in a sentence rather than logical operators, and you'll get a better feel for how to use them.

7 Perl's Regular-Expression Atom Quantifiers Quantifier Matches Example * Zero or more instances of the atom ab*c + ? htm (27 of 31) [2/17/2007 1:23:00 PM] Matches Doesn't Match ac, abb abc abc ac ac, abbc abc Chapter 1 -- Perl Overview {n} {n,} n instances of the atom At least n instances of the atom {nm} At least n, most m instances of the atom ab{2}c abbc abbbc ab{2,}c abbc, abc abbbc ab{2,3}c abbc abbbbcat Special Characters Several special characters are denoted by backslashed letters, with \n being especially familiar to C programmers, perhaps.

0-9]$/ && print "Ends with a digit. "; /perl/ && print "You said it! htm (28 of 31) [2/17/2007 1:23:01 PM] Chapter 1 -- Perl Overview print $prompt; } Bound Matches Matching doesn't always have to operate on $_, although this default behavior is quite convenient. A special operator, =~, evaluates to either true or false, depending on whether its first operand matches on its second operand. So $filename =~ /dat$/ is true if $filename matches on /dat$/. ~, has the opposite sense. ~ /perl/ && warn "Not sure if perl is in your path "; Alternative Delimiters The match operator can use characters other than //-a useful point if you're trying to match a complex expression that involves forward slashes.