perl 的正则表达式匹配(一)

注意: 由于此blog不能显示反斜线，故用&&代替反斜线.

1. Matches with m//.

匹配操作(m/string/) 的简写形式 /string/, 也可以用m/string/的等价式m(string), m, m{string}, m[string],m,string,,m!string!,m^string^,等. 如果匹配，返回true，否则为false

2. Matches Option Modifiers

a. 大小写不敏感选项 /i

如果没有/i，是大小写敏感的.

print "Would you like to play a game? ";
chomp($_ = );
if (/yes/i) { # case-insensitive match
print "In that case, I recommend that you go bowling.n";
}

b. 匹配任何字符 /s

默认情况下.不匹配新行，而只能在一行内匹配，如果加了/s选项则可以匹配新行，就象[&&d&&D]一样能匹配任意字符。

$_ = "I saw Barneyndown at the bowling alleynwith Frednlast night.n";
if (/Barney.*Fred/s) {
print "That string mentions Fred after Barney!n";
}

note:Without the /s modifier, that match would fail since the two names aren't on the same line.

c. 允许模式中的空格选项 /x

默认的模式中如果有空格，表示匹配有空格的string，如果加上 /x 选项则忽略中间空格.(目的是使得模式清晰) 。

/-?d+.?d*/ # what is this doing?
/ -? d+ .? d* /x # a little better

/
-? # an optional minus sign
d+ # one or more digits before the decimal point
.? # an optional decimal point
d* # some optional digits after the decimal point
/x # end of pattern

#good style

d. 选项的复合.

if (/barney.*fred/is) { # both /i and /s
print "That string mentions Fred after Barney!n";
}

3. Anchors 锚.

行首标识符 ^

行尾标识符 $

“词”边界标识符 b, “词”可以由下划线，数字，字母组成。

/&&bfred&&b/将匹配单词fred, 不会匹配frederick, alfred.

/abc123&&b/可以匹配abc123- ，但abc123_却不可以。这就是因为下划线是“词”的边界，而横线不是词的边界。

4. The Binding Operator, =~ (绑定操作符)

默认匹配字符串变量是$_, 如 if (/ string /)....

如果要让指定的变量来匹配则需要绑定操作符 =~, 如下

my $some_other = "I dream of betty rubble.";
if ($some_other =~ /brub/) {
print "Aye, there's the rub.n";
}

又如

print "Do you like Perl? ";
my $likes_perl = ( =~ /byesb/i);
... # Time passes...
if ($likes_perl) {
print "You said earlier that you like Perl, so...n";
...

[@more@]

未完待续

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