📅  最后修改于: 2021-01-07 08:32:13             🧑  作者: Mango
正则表达式是字符的字符串,其限定特定的图案。 perl正则表达式的语法与awk,grep和sed的语法非常相似。
perl中包含三个正则表达式运算符:
Perl匹配运算符具有各种修饰符。它主要用于将字符串或语句与正则表达式匹配。
Operators | Description |
---|---|
cg | Continue search even if the global match fails |
g | Search globally for all matches |
i | Search the match with case insensitivity |
m | If string has a new line character, the $ and ^ will match against a new line boundary instead of string boundary |
o | Allow expression evaluation only once |
s | Use . to match a new line character |
x | Use white space in the expression |
匹配运算符=〜用于匹配给定字符串中的单词。这是区分大小写的,这意味着如果字符串具有小写字母并且您正在搜索大写字母,则它将不匹配。
$line = "This is javaTpoint.";
if ($line =~ /java/){
print "Matching\n";
}else{
print "Not Matching\n";
}
if ($line =~ /Java/){
print "Matching\n";
}else{
print "Not Matching\n";
}
输出:
Matching
Not Matching
它与较早版本(=〜)相反。如果字母匹配,则输出不匹配,反之亦然。
$ line = "This is javaTpoint.";
if ($line!~ /java/){
print "Matching\n";
}else{
print "Not Matching\n";
}
if ($line!~ /Java/){
print "Matching\n";
}else{
print "Not Matching\n";
}
输出:
Not Matching
Matching
您还可以将其与特殊的默认变量$ _匹配。
$_ = "This is javaTpoint.";
if (/java/) {
print "Matching\n";
}
else {
print "Not Matching\n";
}
if (/Java/) {
print "Matching\n";
}
else {
print "Not Matching\n";
}
输出:
Matching
Not Matching
匹配运算符m也用于匹配给定字符串中的单词。
$ line = "This is javaTpoint.";
if ($line=~ m[java]){
print "Matching\n";
}else{
print "Not Matching\n";
}
if ($line=~ m{Java}){
print "Matching\n";
}else{
print "Not Matching\n";
}
输出:
Matching
Not Matching
$ 1,$ 2将根据指定的括号print单词。
my $word = "CuNaHg";
$word =~ /(((Cu)(Na))(Hg))/;
print "1: $1 2: $2 3: $3 4: $4 5: $5 6: $6\n";
输出:
1: CuNaHg 2: CuNa 3: Cu 4: Na 5: Hg 6:
它从给定的字符串在括号内打印匹配的字符。
my $word = "CuNaHg";
$word =~ /(?:(Cu)NaHg)/;
print "$1\n"; # prints "Cu"
$word =~ /(?:Cu(Na)Hg)/;
print "$1\n"; # prints "Na"
$word =~ /(?:CuNa(Hg))/;
print "$1\n"; # prints "Hg?
输出:
Cu
Na
Hg
替换运算符只是匹配运算符的扩展。它允许替换与某些新文本匹配的文本。
其基本语法为:
s/oldPattern/newPattern /;
在这里,我们在第一部分中用s ///将液体替换为固体。
在第二部分中,以s /// g整体将“液体”替换为“固体”。
$line = "liquid will remain liquid until it is evaporated";
$line =~ s/liquid/solid/;
print "$line\n";
print"\n";
$line = "liquid will remain liquid until it is solidified";
$line =~ s/liquid/solid/g;
print "$line\n";
输出:
solid will remain liquid until it is evaporated
solid will remain solid until it is evaporated
翻译运算符与替换运算符符相似。但是转换不使用正则表达式来搜索替换值。
其基本语法为:
tr/oldLetter/newLetter /;
在这里,所有的“ l”字母将由翻译运算符替换为“ z”字母。
$line = "liquid will remain liquid until it is evaporated";
$line =~ tr/l/z/;
print "$line\n";
输出:
ziquid wizz remain ziquid untiz it is evaporated
在这里,翻译运算符会将所有的“ l”和“ i”字母替换为“ z”和“ x”字母。
$line = "liquid will remain liquid until it is evaporated";
$line =~ tr/li/zx/;
print "$line\n";
输出:
zxquxd wxzz remaxn zxquxd untxz xt xs evaporated