Perl_skills.md

PERL小技巧

use strict;
use warnings;

@INC:

########## perl中的INC变量中包含了所有的perl module的查找路径，可以使用perl -V 来查看INC的值

在perl程序中修改INC， 例如：

#!/usr/bin/perl -w
push(@INC,"/home/test");

或者

#!/usr/bin/perl -w
BEGIN{push(@INC,"/home/test")};

或者

#!/usr/bin/perl -w
use lib '/home/test';

FindBin

让脚本在运行时找到其目录的路径，然后通过相对路径找到lib目录，解决执行时模块路径问题

use FindBin;

Example:

use FindBin qw($Bin);
use lib "$Bin/../lib";

FindBin导出标量有：

- $Bin
path to bin directory from where script was invoked

- $Script
basename of script from which perl was invoked

- $RealBin
$Bin with all links resolved

- $RealScript
$Script with all links resolved

qw()

saving you from the tedium of having to quote and comma-separate each element of the list by hand

my @names = qw(Kernighan Ritchie Pike); # is equal to the following
my @names = ('Kernighan', 'Ritchie', 'Pike');

You can use any non-alphanumeric, non-whitespace delimiter to surround the qw() string argument

@names = qw(Kernighan Ritchie Pike);
@names = qw/Kernighan Ritchie Pike/;
@names = qw'Kernighan Ritchie Pike';
@names = qw{Kernighan Ritchie Pike};

#!/usr/bin/perl
use strict;
use warnings;
use File::Temp qw(tempfile tempdir);
# This code fragment has the effect of importing the tempfile and tempdir functions from the File::Temp module. 
# It does this by providing the list 'tempfile', 'tempdir' to the use function.

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perl命令行

perl -e: 让perl程序在命令行运行
perl -n: 让perl可以一行一行处理文件
perl -l: 自动chomp，每一个输出自动加上\n
perl -a: 自动split放入@F
perl -p: 让perl把下面循环添加到脚本
$.: 文件行数

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sort

-n: comparing accoring to string numberic value
-r: reverse the result of comparisons

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perl函数：quotemeta

return the values of EXPR with all the ASCII non-"word" characters backslashed (反斜杠\n).
quotemeta (and \Q ... \E) are useful when interpolating strings into regular expressions, because by default an interpolated variable will be considered a mini-regular expression. For example:

my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
$sentence =~ s{$substring}{big bad wolf};

Will cause $sentence to become 'The big bad wolf jumped over...'.

On the other hand:

my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
$sentence =~ s{\Q$substring\E}{big bad wolf};

Or:

my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
my $quoted_substring = quotemeta($substring);
$sentence =~ s{$quoted_substring}{big bad wolf};