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perl (1987)
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python (1991)
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基础
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模块导入
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use strict;
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import os, re, sys
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版本查看
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$ perl -v
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$ python -V
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执行脚本
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$ perl foo.pl
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$ python foo.py
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交互模式
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$ perl -de 0
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$ python
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执行语句
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$ perl -e 'print("hi\n")'
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$ python -c "print('hi')"
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语句分隔
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;
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\n (newline)
or ;
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语句块
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{}
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Indent
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注释
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# comment
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# comment
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多行注释
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=for
comment line
another line
=cut
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use triple quote string literal:
'''comment line
another line'''
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变量和操作符
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赋值
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$v = 1;
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v = 1
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赋值
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($x, $y, $z) = (1, 2, 3);
# 3 is discarded:
($x, $y) = (1, 2, 3);
# $z set to undef:
($x, $y, $z) = (1, 2);
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x, y, z = 1, 2, 3
# raises ValueError:
x, y = 1, 2, 3
# raises ValueError:
x, y, z = 1, 2
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交换
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($x, $y) = ($y, $x);
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x, y = y, x
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操作符
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+= -= *= none /= %= **=
.= x=
&&= ||= ^=
<<= >>= &= |= ^=
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# do not return values:
+= -= *= /= //= %= **=
+= *=
&= |= ^=
<<= >>= &= |= ^=
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自增
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my $x = 1;
my $y = ++$x;
my $z = --$y;
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none
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局部变量
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my $v;
my (@a, %d);
my $x = 1;
my ($y, $z) = (2, 3);
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# in function body:
v = None
a, d = [], {}
x = 1
y, z = 2, 3
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全局变量
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our ($g1, $g2) = (7, 8);
sub swap_globals {
($g1, $g2) = ($g2, $g1);
}
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g1, g2 = 7, 8
def swap_globals():
global g1, g2
g1, g2 = g2, g1
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常量
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use constant PI => 3.14;
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# uppercase identifiers
# constant by convention
PI = 3.14
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空
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undef
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None
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空测试
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! defined $v
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v == None
v is None
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访问未定义变量
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error under use strict; otherwise undef
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raises NameError
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真假
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1 ""
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True False
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假
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undef 0 0.0 "" "0" ()
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False None 0 0.0 '' [] {}
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逻辑运算
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&& || !
lower precedence:
and or xor not
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and or not
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条件
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$x > 0 ? $x : -$x
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x if x > 0 else -x
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比较
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numbers only: == != > < >= <=
strings: eq ne gt lt ge le
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comparison operators are chainable:
== != > < >= <=
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数学运算
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类型转化
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7 + "12"
73.9 + ".037"
"value: " . 8
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7 + int('12')
73.9 + float('.037')
'value: ' + str(8)
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算术运算
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+ - * / none % **
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+ - * / // % **
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取余
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int ( 13 / 5 )
none
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13 // 5
q, r = divmod(13, 5)
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浮点除法
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13 / 5
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float(13) / 5
# Python 3:
13 / 5
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数学函数
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use Math::Trig qw(
tan asin acos atan);
sqrt exp log sin cos tan asin acos atan atan2
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from math import sqrt, exp, log, \
sin, cos, tan, asin, acos, atan, atan2
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四舍五入
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# cpan -i Number::Format
use Number::Format 'round';
use POSIX qw(ceil floor);
int($x)
round($x, 0)
ceil($x)
floor($x)
abs($x)
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import math
int(x)
int(round(x))
math.ceil(x)
math.floor(x)
abs(x)
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最大最小
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use List::Util qw(min max);
min(1,2,3);
max(1,2,3);
@a = (1,2,3);
min(@a);
max(@a);
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min(1,2,3)
max(1,2,3)
min([1,2,3])
max([1,2,3])
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除0
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error
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raises ZeroDivisionError
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大整数
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converted to float; use Math::BigInt to create arbitrary length integers
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becomes arbitrary length integer of type long
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大浮点数
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inf
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raises OverflowError
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随机数
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int(rand() * 100)
rand()
none
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import random
random.randint(0,99)
random.random()
random.gauss(0,1)
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随机数
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srand 17;
my $sd = srand;
srand($sd);
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import random
random.seed(17)
sd = random.getstate()
random.setstate(sd)
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位操作
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<< >> & | ^ ~
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<< >> & | ^ ~
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其他进制
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0b101010
052
0x2a
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0b101010
052
0x2a
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字符串操作
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字符串
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"don't say \"no\""
'don\'t say "no"'
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'don\'t say "no"'
"don't say \"no\""
"don't " 'say "no"'
'''don't say "no"'''
"""don't say "no\""""
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多行字符串
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yes
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triple quote literals only
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转义
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double quoted:
\a \b \cx \e \f \n \r \t \xhh \x{hhhh} \ooo Perl 5.14: \o{ooo}
single quoted:
\' \\
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single and double quoted:
\newline \\ \' \" \a \b \f \n \r \t \v \ooo \xhh
Python 3:
\uhhhh \Uhhhhhhhh
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变量替换
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my $count = 3;
my $item = "ball";
print "$count ${item}s\n";
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count = 3
item = 'ball'
print(‘%s %s’ % (count, item))
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sprintf
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my $fmt = "lorem %s %d %f";
sprintf($fmt, "ipsum", 13, 3.7)
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'lorem %s %d %f' % ('ipsum', 13, 3.7)
fmt = 'lorem {0} {1} {2}'
fmt.format('ipsum', 13, 3.7)
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here document
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$word = "amet";
$s = <<EOF;
lorem ipsum
dolor sit $word
EOF
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‘’’
‘’’
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字符串连接
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my $s = "Hello, ";
my $s2 = $s . "World!";
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s = 'Hello, '
s2 = s + 'World!'
juxtaposition can be used to concatenate literals:
s2 = 'Hello, ' "World!"
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字符串复制
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my $hbar = "-" x 80;
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hbar = '-' * 80
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字符串分隔
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split(/\s+/, "do re mi fa")
split(/\s+/, "do re mi fa", 2)
split(/(\s+)/, "do re mi fa");
split(//, "abcd")
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'do re mi fa'.split()
'do re mi fa'.split(None, 1)
re.split('(\s+)', 'do re mi fa')
list('abcd')
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字符串连接
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join(" ", qw(do re mi fa))
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' '.join(['do', 're', 'mi', 'fa'])
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字符串大小写
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uc("lorem")
lc("LOREM")
ucfirst("lorem")
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'lorem'.upper()
'LOREM'.lower()
'lorem'.capitalize()
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字符串strip
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# cpan -i Text::Trim
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