1. tr 转换 转换不是替换（tr///==y///）

tr/searchlist/replacementlist/用于查找某个一个字符串，并用replacementlist替换，可以使用正则表达式

my $str="this Is A teST";

$str=~tr/a-z/A-Z/; 把小写转换为大写 会输出THIS IS A TEST

s///  options

g 全局替换

i 忽略大小写

my $str3="this is a test\n";

$str3=~s/t/haha/g;                  =====>hahahis is a hahaeshaha
print $str3;
$str3=~s/HaHa/t/ig;                 =====>this is a test
print $str3;            

this is a test

tr 与 替换的区别

 tr可以使用正则表达式，替换不行，没法使用$str=~s/a-z/A-Z/; 不会有任何改变 tr/ab/ABC/ 替换原则是a->A b->B   而s/ab/ABC/会将ab->ABC

• tr///

  The transliteration operator. Same as y///. 

$count  = $str3=~ tr/i/i/; # count the stars in $sky   count  the number of a and store into $count

统计i的个数存放在$count

#!/usr/bin/perl
use strict;
my $str1="this Is A tr TEST";
my $str2="this Is A tr TEST";
$str1=~s/t/T/g;
$str2=~tr/a-z/A-Z/;
print "$str1\n";
print "$str2\n";
my $str3="this is a test\n";
my $count=$str3=~tr/i/i/;
print "\ncount the number of i --->$count<----\n";

结果：

D:\>perl tr.pl
This Is A Tr TEST
THIS IS A TR TEST

count the number of i --->2<----

tr  Options: