substr实例

1.1 Problem

  You want to access or modify just a portion of a string, not the whole thing. For instance, you've read a fixed-width record and want to extract individual fields.

1.1.2 Solution

Thesubstrfunction lets you read from and write to specific portions of the string.

$value = substr($string, $offset, $count);
$value = substr($string, $offset);
substr($string, $offset, $count) = $newstring;
substr($string, $offset, $count, $newstring);  # same as previous
substr($string, $offset)         = $newtail

Use the=~operator and thes///,m//, ortr///operators in conjunction withsubstrto make them affect only that portion of the string.
1.1.3 Example
#!/usr/bin/perl 
use warnings;
use 5.010;

#1.use 'substr' function to read specific portions of the string
my $string = "This is what you have";

my $first = substr($string,0,1); #"T"
my $start = substr($string,5,2); #"is"
my $rest = substr($string,13); #"you have"
my $last = substr($string,-1); #"e"
my $end = substr($string,-1,4); #"have"
my $piece = substr($string,-8,3); #"you"
say $string;


#2.use 'substr' function to write specific portions to the string
#my $string = "This is what you have"
#substr($string,5,2) = "wasn't"; # change "is" to "wasn't"
substr($string,5,2,"wasn't"); #same as previous
say $string; #This wasn't what you have

substr($string,-12) = "ondrous";
say $string; #This wasn't wondrous

substr($string,0,1) = ""; #delete the first character
say $string; #his wasn't wondrous

substr($string,-10) = ""; #delete last 10 characters
say $string; #his wasn'

#3.use the =~ operator and the s///,m//,or tr/// operators
#in conjuncation with substr function to make them affect
#only that portion of the string

my $pattern = "[a-zA-Z]";
if(substr($string,-10) =~ /$pattern/){
    print "Pattern matches in last 10 characters\n";
}

substr($string,0,5) =~ s/is/e/g;
say $string;

#exchange the first and last letters in a string
my $a = "make a hat";
(substr($a,0,1),substr($a,-1))=(substr($a,-1),substr($a,0,1));
say $a;