第四章 语言和声明

4.1 简单语句


一个简单语句是一个表达式,因为副作用而计算。每条简单语句都必须以分号结尾,除非它是一个块中的最后一句。


4.2 if else 语句:


[oracle@jhoa 20150319]$ cat 1.pl 
if (( my $color = <STDIN>) =~ /red/i ) {
      $value = 1;
}
elsif ($color =~ /green/i) {
      $value = 2;
}
elsif ($color =~ /blue/i) {
  $value = 3;
}
else {
     print "unknown"; $value=4;
}
print "$value is $value ";


4.3.3 foreach 循环:




累加 $value
[oracle@jhoa 20150319]$ cat 2.pl 
@array = qw/1 2 3 4 5 6 7 8 9 10/;


$sum = 0; foreach $value (@array) { $sum += $value }
print "$sum is $sum ";
[oracle@jhoa 20150319]$ perl 2.pl 
$sum is 55


[oracle@jhoa 20150319]$ cat 2.pl 
@array = qw/1 2 3 4 5 6 7 8 9 10/;


$sum = 0; foreach $value (@array) { $sum = $value + $sum }
print "$sum is $sum ";
[oracle@jhoa 20150319]$ 
[oracle@jhoa 20150319]$ perl 2.pl 
$sum is 55




last 退出循环:


[oracle@jhoa 20150319]$ cat 4.pl 
for ($i = 2;$i<10;$i=$i+2){
  for ($j=3;$j <5;$j++){
    if ($i > $j){
   last; ###退出内层循环
   }
  print "1--$i is $i ";
  print "1--$j is $j ";
    }
print "2---$i is $i "; 
print "2---$j is $j "; 
}
[oracle@jhoa 20150319]$ perl 4.pl 
1--$i is 2
1--$j is 3
1--$i is 2
1--$j is 4
2---$i is 2
2---$j is 5
2---$i is 4
2---$j is 3
2---$i is 6
2---$j is 3
2---$i is 8
2---$j is 3


for ($j=3;$j <5;$j++){  这层循环退出






4.4 光块




return 只能用于子程序(或者eval)块


[oracle@jhoa 20150319]$ cat 5.pl 
$var="111111";
return 1;
[oracle@jhoa 20150319]$ perl 5.pl 
Can't return outside a subroutine at 5.pl line 2.


$dbh = DBI->connect("dbi:Oracle:$DATABASE", "$USERID", "$PASSWORD", {PrintError => 0});


$dbh->do("TRUNCATE TABLE $DESTSCHEMA.F_EVT_CADC_SRLFREEZE") or die($DBI::errstr);






闭包:






[oracle@jhoa 20150319]$ cat a1.pl 
use strict;
$var='aaaaaa';


[oracle@jhoa 20150319]$ perl a1.pl 
Global symbol "$var" requires explicit package name at a1.pl line 2.
Execution of a1.pl aborted due to compilation errors.


 use strict会限制全局变量的使用


use strict;
our $var='aaaaaa';


明确声明全局变量




为了又更好的颗粒度和提高效率,你可以用圆括号捕捉你特别想分离出来的部分。每对圆括弧捕捉与圆括弧内的


模式相匹配的子模式。圆括弧由左圆括弧的位置从左到右一次排序,对应的那些子模式的子字串在匹配之后可以


通过顺序的变量$1,$2,$3等等获得:


[oracle@jhoa 20150319]$ cat a2.pl 
$_ = "Bilbo Baggins's birthday is September 22";
/(.*)'s birthday is (.*)/;
print "Person:$1 ";
print "Person:$2 ";


[oracle@jhoa 20150319]$ perl a2.pl 
Person:Bilbo Baggins 
Person:September 22