Perl指令碼 雜記

Perl指令碼 雜記

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Perl指令碼：

Perl chdir函式2010年10月29日 星期五 下午 16:24用法：

chdir EXPR

chdir介紹：

如果可能，chdir函式改變當前程式的工作目錄到EXPR。如果省略EXPR，即返回撥用者的根目錄。成功時返回真，否則返回假。

例子：

假設根目錄/home/zhenglc:

#!/usr/bin/perl

chdir "/usr/home";

# Now you are in /usr/home dir.

chdir;

# Now you are in home directory /home/zhenglc又或者是用perl的單行命令：

perl -e 'chdir; print `pwd`'

#輸出：/home/zhenglc

perl -e 'chdir "/home/zhenglc/temp/"; print `pwd`'

#輸出：/home/zhenglc/temp

##pwd是shell命令。返回當前的路徑。chdir函式相當於Linux的命令cd。

#!/usr/bin/perl

use strict;

use warnings;

my $dir_out = "/data4/nba_show_traffic/";

system "mkdir","-p",$dir_out;

my $dir = "/data4/nba_sw_int_traffic/";

chdir $dir || die "Can't change dir $dir $!n";

my @files = glob ("*"); #陣列變數將儲存該目錄下所有檔名,除了以點號開頭的隱藏檔案.

foreach my $file (@files)

{

$file =~ m/(d{1,3}.d{1,3}.d{1,3}.d{1,3})/;#匹配任意ip地址，m是匹配，match，這個地方沒有做容錯，程式設計者知道肯定是能匹配上的。

print "$1n";#列印出匹配上的那個ip地址

my $f_out = $dir_out.$file;

open FH,"

open FH_OUT,">",$f_out || die "Can't open $f_out $!n";

while()

{

if(/GigabitEthernet0/1/)

{

print FH_OUT $_;

}

}

close FH_OUT;

close FH;

}

Perl中index的用法，

Introduction

The index() function is used to determine the position of a letter or a substring in a string. For example, in the word "frog" the letter "f" is in position 0, the "r" in position 1, the "o" in 2 and the "g" in 3. The substring "ro" is in position 1. Depending on what you are trying to achieve, the index() function may be faster or more easy to understand than using a regular expression or the split() function.

Example 1a. Where in a string is a certain letter?

Let's say you are trying to determine if a word has a particular letter in it. Let's look for the letter "l" in the string "perlmeme.org".

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'l';

my $result = index($string, $char);

print "Result: $resultn";

This program gives you:

Result: 3

Example 1b. The string doesn't contain the letter?

If the string doesn't contain the letter, index() will return a -1. For example, we can look for the letter "L" in the string "perlmeme.org":

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'L';

my $result = index($string, $char);

print "Result: $resultn";

The program outputs:

Result: -1

Example 1c. The string contains more than one of the letter?

If the letter we're searching for appears more than once in the string, index() return the index of the first occurrence of the letter.

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'e';

my $result = index($string, $char);

print "Result: $resultn";

This program gives you:

Result: 1

Example 2. Looking for a substring

Looking for a substring (rather than a single character) works in exactly the same way as looking for a single character:

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $substr = 'me';

my $result = index($string, $substr);

print "Result: $resultn";

This program gives you:

Result: 4

Example 3a. What if I don't want the first occurrence?

The index() function let's you specify an offset. This tells index() where to start looking in the string. In our example, we found the first occurrence of the letter 'e' at position 1. Let's try to find the second:

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'e';

# The first 'e' was at position 1, so let's start

# looking again at position 2

my $offset = 2;

my $result = index($string, $char, $offset);

print "Result: $resultn";

The program outputs:

Result: 5

Example 3b. How to find every occurrence

To find (and do something with) every occurrence of a character in a string, you could use index() in a loop, incrementing the offset each time:

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'e';

my $offset = 0;

my $result = index($string, $char, $offset);

while ($result != -1) {

print "Found $char at $resultn";

$offset = $result + 1;

$result = index($string, $char, $offset);

}

When we run this program, we get the following output:

Found e at 1

Found e at 5

Found e at 7

Example 4. How to find the last occurrence

Instead of looping through every occurrence of a letter in a string to find the last one, you can use the rindex() function. This works exactly the same as index() but it starts at the end of the string. The index value returned is string from the start of the string though.

#!/usr/bin/perl

use strict;

use warnings;

my $string = 'perlmeme.org';

my $char = 'e';

my $result = rindex($string, $char);

print "Result: $resultn";

This would produce:

Result: 7

Perl指令碼一小例子：

echo "aaTbbT"|perl -ne "for $i (split /T/){print $i;}"#這裡將for改成foreach也可以，split/T/可以改成split(“:”)或split(“:”,$_)

結果：aabb