Perl 学习手札之八： Operators

数值的比较运算符：+， -， *， /， ++， --；

arithemetic.pl

#!/usr/bin/perl
use strict;
use warnings;

main(@ARGV);

sub main
{
    my $n=42 + 12;# repeat with - * /
    message("The number is: " . $n);    
    my $n =42;
    #$n++;
    #$n--;
    #++$n;
    message("The number is: " . $n++);
    message("The number is: " . ++$n);
    message("The number is: " . --$n);
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

数值的运算符，还有++，--，这些都是和C里面完全相同。

还有就是关于比较运算符：

comparition.pl

#!/usr/bin/perl

use strict;
use warnings;

main(@ARGV);

sub main
{
#    if(5<=5){
#    if(6>5){
#    if(6>==5){
#    if("five" eq "five"){
    if("six" gt "five"){
        message("this is true");
    }else{
        message("this is NOT true");
    }
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

以上是关于字符，数字的比较运算符，这个完全可以参照perldoc perlop来看更详细的解释。

logical.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    my $x = (5!=5);
    message("x is '$x'");
    if((5==6||(6==5))){
#    if((5==6)&&(6==5)){
#    if((5==6) and (6==5)){
#    if((5==6) or (6==5)){        
                message("this is true");
    }else{
        message("this is not true");
    }
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

注意此时的 || 等价与or; &&等价与 and。

filetest.pl

#!/usr/bin/perl
use strict;
use warnings;

main(@ARGV);

sub main
{
    my @dirlist = <*>;
    foreach my $fn (@dirlist){
        message($fn);
        if( -f $fn){
            my $size = -s $fn;
            message("$fn is a plan file($size bytes)");
        }elsif( -d $fn){
            message("$fn is a directory");
        }else{
            message("$fn is something else");
        }
    }
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

文件测试，可以查询相应的章节，或者在eclips的环境下，选中-f，然后点击右键，选中perldoc。

range.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
#    print foreach (1..9);
#    print foreach ('a'..'z','A'..'Z');
#    print foreach ('00'..'31');
    print join(',', ('00'..'31'));    
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

我们会发现，range操作符还是很有用处的^^.

concatenation.pl

#!/usr/bin/perl

use strict;
use warnings;

main(@ARGV);

sub main
{
    my $s1="string 1";
    my $s2 = "string 2";
    message($s1.' '.$s2);
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

连接运算符 . 也是经常会见到的运算符。

quoteop.pl

#!/usr/bin/perl


#
use strict;
use warnings;

main(@ARGV);

sub main
{
    message("This is the \"template.pl\" exercise file from Perl 5 Essential Training.");
    message(q[This is the "template.pl" exercise file from Perl 5 Essential Training.]);
    message(q/This is the \"template.pl\" exercise file from Perl 5 Essential Training./);
    message(q{This is the \"template.pl\" exercise file from Perl 5 Essential Training.});
    my $x=42;
    message(q{This is the "template.pl" ($x)exercise file from Perl 5 Essential Training.});
    message(qq{This is the "template.pl" ($x)exercise file from Perl 5 Essential Training.});

}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

这个可以参考qq和q的差别，也就是双引号和单引号的差别。

precedence.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    my $n = 3+7*5;
    message($n);
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

可以参照programming perl里面的运算符的优先级表。

或者本目录下的附件：

Operator Precedence.txt

Operator Precedence and Associativity in Perl
=============================================

left        terms and list operators (leftward)
left        ->
nonassoc    ++ --
right       **
right       ! ~ \ and unary + and -
left        =~ !~
left        * / % x
left        + - .
left        << >>
nonassoc    named unary operators
nonassoc    < > <= >= lt gt le ge
nonassoc    == != <=> eq ne cmp ~~
left        &
left        | ^
left        &&
left        || //
nonassoc    .. ...
right       ?:
right       = += -= *= etc.
left        , =>
nonassoc    list operators (rightward)
right       not
left        and
left        or xor