Perl
数组
定义数组：
@n1=(1,5,2,3,7,9);
($q, $w, $e, $r) = @n1;
print("Numbers: @n1\n");
print("elems are: $q, $w, $e, $r\n");
Numbers: 1 5 2 3 7 9
elems are: 1, 5, 2, 3
获取长度用$#a+1或者$a.""
#!/usr/bin/perl -w
$a[0] = "My 1st string.";
$a[1] = "My 2nd string.";
$a[2] = 333;
# another way to define an array
@b = ("123", 456, "789");
# get last index of array
print("Index of last elem is:",$#a, "\n");
# get total num
print("Total elem num is: ",$#a+1, "\n");
# another way to get total num
print("Array length is: ",@a."" , "\n");
$bn = @b;
$bp = "@b";
print("b number is: ",$bn, "\n");
print("b content are: ",$bp, "\n");
(base) ➜ perl git:(master) ✗ perl aray_num.pl
Index of last elem is:2
Total elem num is: 3
Array length is: 3
b number is: 3
b content are: 123 456 789
哈希
%a_hash = ('name' => 'Xin', 'age' =>22);
KV类型，类似python的dict，key无序。
读数据：$a_hash{'name'}
添加key:$a_hash{'gender'}='F'; 类似python的defaultdict，可以直接对未定义的key赋值。
删除key：delete($a_hash{'gender'});
#!/usr/bin/perl -w
%a_hash = ('name' => 'Xin', 'age' =>22);
$a_hash{'gender'}='F';
for $key (keys %a_hash){
print("$key is $a_hash{$key}\n");
}
(base) ➜ perl git:(master) ✗ perl hashy.pl
age is 22
name is Xin
gender is F
变量
三种数据类型：
$a_scalar = 10;
@an_array = (1, 2, 3);
$a_hash = ('name' => 'Xin', 'age' =>22);
Perl 只有全局变量, 没有局部变量。
局部变量要加my关键字，eg：my $var 才是局部变量。
交换两变量的值
($a, $b) = ($b, $a);
读入数据
从 STDIN 读入数据
#!/usr/bin/perl -w
# Read from input
$ipt = <STDIN>;
while(defined($ipt)){
print "$ipt";
$ipt = <STDIN>;
}
####################
while(<STDIN>){
print $_;
}
####################
foreach $line(<STDIN>){
print "$line";
}
https://paste.ubuntu.com/p/5CKBMhTDpr/
从文件读入
尖括号中间是文件句柄，尖括号运算符允许你读取文件句柄，比如
文件句柄需要使用尖括号包括。
#!/usr/bin/perl -w
$filename = $ARGV[0];
open(F, '<', $filename) or die $!;
# filehandle variable need angle brackets <F>
foreach $line(<F>){
print "$line";
}
close F;
写文件
#!/usr/bin/perl -w
$filename = 'output.txt';
@num = (1..10);
open(FR, '>', $filename) or die $!;
foreach $n(@num){
print FR "$n\n";
}
close(FR);
<> 用法
从ARGV读入，如空，则从stdin读入。
<> is shorthand for "read from the files specified in @ARGV, or if @ARGV is empty, then read from STDIN".
操作
比较 cmp
<=> 比较数值
cmp 比较字符，比较数字时是按位比较。 eg: 12 cmp 100 is 1 (12>100)，因为按位 1 == 1, 2 >0。
-2 <=> -3 is 1， -2 > -3，与数学一致。
排序 sort
默认逐字符比较。
#!/usr/bin/perl -w
@a = ("Hangzhou Zhejiang", "Peking Beijing", "Anyang Henan", "Zhengzhou Henan", "Sydney NSW", "Zibo Shandong");
@sorted = sort @a;
print(join(', ', @sorted));
(base) ➜ perl git:(master) ✗ perl array2.pl
Anyang Henan, Hangzhou Zhejiang, Peking Beijing, Sydney NSW, Zhengzhou Henan, Zibo Shandong%
根据字符长度。
@sorted = sort {length($a) cmp length($b)} @a;
(base) ➜ perl git:(master) ✗ perl array2.pl
Sydney NSW, Anyang Henan, Zibo Shandong, Peking Beijing, Zhengzhou Henan, Hangzhou Zhejiang
根据省份
#!/usr/bin/perl -w
@a = ("Hangzhou Zhejiang", "Peking Beijing", "Anyang Henan", "Zhengzhou Henan", "Sydney NSW", "Zibo Shandong");
sub State{
return (split(/ /, $_[0]))[1];
}
@sorted = sort {State($a) cmp State($b)} @a;
print(join(', ', @sorted));
(base) ➜ perl git:(master) ✗ perl array2.pl
Peking Beijing, Anyang Henan, Zhengzhou Henan, Sydney NSW, Zibo Shandong, Hangzhou Zhejiang%
多条件筛选，先判断城市长度，当内容长度一样时再根据省份筛选。
sort {length($a) cmp length($b) || State($a) cmp State($b)}，当length($a) cmp length($b) 一致时返回0，随后进入or的后半条件中，不一致时（1或-1）不会判断后半State($a) cmp State($b)。
倒序排序 Reverse sort
三种方法
- 交换$a $b顺序
- 在（正序）结果前加
-，对结果取返 - 使用
reverse sort
#!/usr/bin/perl -w
@a = (1,2,3,4,5,6,7);
@s1 = sort {$b <=> $a} @a;
print(join(', ', @s1));
@s2 = sort {- ($a <=> $b)} @a;
print(join(', ', @s2));
@s3 = reverse sort {$a <=> $b} @a;
print(join(', ', @s3));
(base) ➜ perl git:(master) ✗ perl reverse_sort.pl
7, 6, 5, 4, 3, 2, 17, 6, 5, 4, 3, 2, 17, 6, 5, 4, 3, 2, 1%
小抄速记
字符串转小写
lc lowercase，转小写。
#!/usr/bin/perl -w
$word="Alex";
print(lc $word);
(base) ➜ perl git:(master) ✗ perl lc.pl
alex%
向上、向下取整
使用POSIX 模块的floor()和ceil()函数。
(base) ➜ playground cat floor.pl
#!/usr/bin/perl -w
use POSIX;
$i=23.123;
print("Result of floor is: ", floor($i), "\n");
print("Result of ceil is: ", ceil($i), "\n");
(base) ➜ playground perl floor.pl
Result of floor is: 23
Result of ceil is: 24
文件比较
use File::Compare;模块的compare()函数，文件不同会返回1。
(base) ➜ playground cat compare.pl
#!/usr/bin/perl -w
#
use File::Compare;
$f1 = $ARGV[0];
$f2 = $ARGV[1];
$ans = compare("$f1", "$f2");
print($ans);
(base) ➜ playground ./compare.pl 1.txt 2.txt
1%
(base) ➜ playground ./compare.pl 1.txt 1.txt
0%
正则匹配
Global matching 全局匹配
全局匹配返回一个@array，包括了满足条件的所有结果。
(base) ➜ playground cat regex_2.pl
#!/usr/bin/perl -w
$str = "apple banana capsicum";
for $word ($str =~ /(\w+)/g){
print("$word\n");
}
(base) ➜ playground perl regex_2.pl
apple
banana
capsicum
(base) ➜ playground cat regex_3.pl
#!/usr/bin/perl -w
$str = "apple banana capsicum";
while ($str =~ /(\w+)/g) {
print("Word is $1, ends at position ", pos $str, "\n");
}
(base) ➜ playground perl regex_3.pl
Word is apple, ends at position 5
Word is banana, ends at position 12
Word is capsicum, ends at position 21
ref:
字符串匹配
将pattern替换为replacement，使用 s///格式，其中s///只匹配一次，s///g匹配多次（全局匹配）。
$string =~ s/pattern/replacement/g;
Eg： 去掉字符中多余的tab和空格。
$a = "Hi \t Nih a \w o";
$b = "HiNihao";
$a =~ s/[\t ]+//g;
Eg： 单次匹配与全局匹配。
$x = "I batted 4 for 4";
$x =~ s/4/four/; # $x contains "I batted four for 4"
$x = "I batted 4 for 4";
$x =~ s/4/four/g; # $x contains "I batted four for four"
字符串提取
用()小括号标记grouped pattern，然后用$1提取。
$y = "'quoted words'";
$y =~ s/^'(.*)'$/$1/; # strip single quotes,
# $y contains "quoted words"
或者在第二行使用$1接收。
$line =~ /"species": "(.*)"/)
$curr_species = $1;
ref:
perlrequick - perldoc.perl.org
字符串提取为list
使用split()可以将字符串按条件提取为list。
用法为split(/Pattern/, Expression)。
$x = "Apple Banana Capsicum Kiwi";
@word = split /\s+/, $x; # Apple Banana Capsicum Kiwi
行内生成式
可以将for语句写在表达式之后，eg:
#!/usr/bin/perl -w
for (<>){
print(join(' ', reverse split), "\n");
}
可以写为
#!/usr/bin/perl -w
print(join(' ', reverse split), "\n") for (<>);
更简便的一句话写法
在perlrun手册中，-p参数可以在你的程序中假设以下循环。
#!/usr/bin/perl -w -p
$_ = join(' ', reverse split). "\n";