The regular expression of Perl--pattern matching

We have used UNIX or Linux systems, not unfamiliar with tools such as Vi,sed,grep,awk, you should know the regular expressions and metacharacters for the delimiter search pattern. So what is a regular expression? A regular expression is a sequence or character pattern that is responsible for string matching of text content when searching or replacing text. Simple regular expressions consist directly of a string or character set to be matched.

Regular expressions are typically delimited by a slash (/). Virtually any string can be a delimiter. For example:/abc/, ABC?

Expression modifiers and simple statements

Common modifiers: If unless while until foreach

If condition modifier

Format Expression2 If Expression1 if the Expression1 expression is true, the Expression2 expression content is executed.

Demo

(1) $x = 5;

Print $x if x==5; ====> Output 5

(2) $_= "xabcy\n";

Print if/abc/; ====> Output Xabcy

(3) $_= "I lost my gloves in the clover.";

Print "Found Love in gloves!\n" if/love/; ====> output found love in gloves!

Unless modifier

Format Expression2 unless Expression1 if the Expression1 is false, the Expression2 expression content is executed.

Demo

(1) $x = 5;

Print $x unless $x ==6; ====> Output 5

While loop modifier

Format Expression2 while Expression1 when the first expression is true, the while loop modifier executes the second expression repeatedly.

Demo

(1) $x = 1;

Print $x + +, "\ n" while $x!=5; ====> Output 1,2,3,4

Until modifier

Format Expression2 until Expression1 as long as the first expression is false, the while loop modifier repeats the second expression

Demo

(1) $x = 1;

Print $x + +, "/n" until $x ==5; ====> Output 1,2,3,4

foreach modifier

The values of each element in the list are judged one by one, and the individual list elements are referenced by scalar $_.

Demo

(1) @alpha = (A.. z, "\ n");

Print foreach @alpha; ====>abcdefghijkmnopqrstuvwxyz

Regular-expression operators

M operator and match

Demo

(1) while (<DATA>) {

Print if/betty/====> output Betty Boop

}

__data__

Steve Blenheim

Betty Boop

Igor Chevsky

Norma Cord

(2) while (<DATA>) {

print if m#jon#; ====> output Jon DeLoach

}

__data__

Steve Blenheim

Betty Boop

Igor Chevsky

Norma Cord

Jon DeLoach

G Global Modifier

I modifier: case insensitive

Demo

(1) $_= "I lost my gloves in the clover,love.";

@list =/love/gi;

Print "@list.    \ n "; ====>love Love Love

The X-expression modifier is used to place comments or white-space characters in a regular expression so that the meaning of the regular expression is more explicit.

Demo

(1) $_= "San Francisco to Hong Kong \ n";

/francisco

/x;

Print "Comments and spaces were removed and \$& is $&\n"; ====> output comments and spaces were removed and $& is Francisco

s operator vs. replace

Demo

(1) $_= "Knock at Heaven ' s door. \ n ";

s/knock/"Knock," * * *. Knocking "/EI;

Print "He ' s $_"; ====>he ' s knock,knock,knocking at heaven ' s door.

Pattern-binding operators

=~  !~

Demo

(1) while ($_=<data>) {

Print $_if $_=~/igor/; ====> output Igor Chevsky

}

__data__

Steve Blenheim

Betty Boop

Igor Chevsky

Norma Cord

(2) while ($_=<data>) {

Print $_ if $_!~/igor/; ====> Enter a name other than Igor Chevsky

}

__data__

Steve Blenheim

Betty Boop

Igor Chevsky

Norma Cord

The regular expression of Perl--pattern matching