1. Perl environment configuration
1. Get perl
Perl is usually located in /usr/local/bin/perl or /usr/bin/perl. You can get it for free using anonymous FTP on the Internet, such as ftp://prep.ai.mit.edu/pub/gnu/perl-5.004.tar.gz
2. The installation process is:
(1) Unzip:
$gunzip perl-5.004.tar.gz
$tar xvf - <perl-5.004.tar.gz
(2) Compile:
$make makefile
(3) Place:
compile the generated Copy the executable file to the directory where the executable file usually resides, such as:
$copy <compiled excutable file> /usr/local/bin/perl
3. Run
Edit your Perl program with a text editor, add the executable attribute: $chmod +x <program> to execute: $./<program>. If the system prompts: "/usr/local/bin/perl not found", it means that you did not install successfully, please reinstall.
Note: The first line of your program must be #!/usr/local/bin/perl (where perl is located).
4 Comments:
The way to comment is to use the character # at the beginning of the statement, such as:
# this line is a comment
Note: It is recommended to use comments frequently to make your program easy to read, which is a good programming practice.
Second, constants, variables and other issues
1. Single quotes and double quotes
Simple variable substitution is supported in strings inside double quotes For example: $text = "This text contains the number $number."; escape
characters are supported in strings inside double
quotes There are two differences between double-quoted strings. One is that there is no variable substitution function, and the other is that backslash does not support escape characters.
2. Repetition and connection
Repeat: print "t" x 5 (5 ts will be output, note: where x is a lowercase x in English letters)
Connection: $a.="bc" (equivalent to even equal)
3. Simple variables, Array, list
Simple variable: declare with $, such as: $a="hello";
array: declare with @, such as: @arr=('a','b','c');
list: the list is contained in A sequence of values in brackets, which can be any value or empty, such as: (1, 5.3 , "hello" , 2), an empty list: ()
3. File operation
1. Open the file: such as open (MYFILE, "file1") || die ("Could not open file"); MYFILE is the declared file handle, file1 is the file name/file path, the whole line of code means: if the opening fails , then output "Could not open file";
close the file: when the file operation is completed, use close(MYFILE); to close the file.
2. Read the file
Statement $line = <MYFILE>; Read a line of data from the file and store it in the simple variable $line and move the file pointer backward by one line. <STDIN> is a standard input file, which is usually input by keyboard and does not need to be opened.
The statement @array = <MYFILE>; reads the entire content of the file into the array @array, and each line of the file (including the carriage return) is an element of @array.
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3. The form of writing a file
is:
open(OUTFILE, ">outfile");
print OUTFILE ("Here is an output line.\n");
Note: STDOUT, STDERR are standard output and standard error files, usually the screen, and No need to open.
4. Judging the file status
1. The file test operator syntax
is: -op expr, such as:
if (-e "/path/file1") { print STDERR ("File file1 exists.\n"); }
file test operator
| operator | describe |
| -b | Is it a block device |
| -c | Is it a character device |
| -d | Is it a directory |
| -e | does it exist |
| -f | Is it an ordinary file |
| -g | Is the setgid bit set |
| -k | Whether the sticky bit is set |
| -l | Is it a symbolic link |
| -o | Do you own the file |
| -p | Is it a pipeline |
| -r | Is it readable |
| -s | Is it non-empty |
| -t | Is it a terminal |
| -u | Whether the setuid bit is set |
| -w | Is it writable |
| -x | Is it executable |
| -z | Is it an empty file |
| -A | how long since last visit |
| -B | Is it a binary file |
| -C | How long since the inode of the file was last accessed |
| -M | How long ago was last modified |
| -O | Is it only owned by "real users" |
| -R | Is it only readable by "real users" |
| -S | Is it socket |
| -T | Is it a text file |
| -W | Whether only "real users" can write |
| -X | Whether only "real users" can execute |
| Note: "Real user" refers to the userid specified when logging in, which is opposite to the current process user ID. The command suid can change the effective user ID. | |
例：
unless (open(INFILE, "infile")) {
die ("Input file infile cannot be opened.\n");
}
if (-e "outfile") {
die ("Output file outfile already exists.\n");
}
unless (open(OUTFILE, ">outfile")) {
die ("Output file outfile cannot be opened.\n");
}
等价于
open(INFILE, "infile") && !(-e "outfile") &&
open(OUTFILE, ">outfile") || die("Cannot open files\n");
四、模式匹配：
1.概念：模式指在字符串中寻找的特定序列的字符，由反斜线包含：/def/即模式def。其用法如结合函数split将字符串用某模式分成多个单词：@array = split(/ /, $line);
2.匹配操作符 =~、!~
=~检验匹配是否成功：$result = $var =~ /abc/;若在该字符串中找到了该模式，则返回非零值，即true，不匹配则返回0，即false。!~则相反。
五、控制结构
(1)、条件判断：if()elseif()else();
(2)、循环：
1、while循环
2、until循环
3、for循环
4、针对列表(数组)每个元素的foreach循环
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5、do循环
6、循环控制:退出循环为last，与C中的break作用相同；执行下一个循环为next，与C中的continue作用相同；PERL特有的一个命令是redo，其含义是重复此次循环，即循环变量不变，回到循环起始点，但要注意，redo命令在do循环中不起作用。
7、传统的goto语句:goto label;
(3)、单行条件
语法为statement keyword condexpr。其中keyword可为if、unless、while或until，如：
print ("This is zero.\n") if ($var == 0);
print ("This is zero.\n") unless ($var != 0);
print ("Not zero yet.\n") while ($var-- > 0);
print ("Not zero yet.\n") until ($var-- == 0);
虽然条件判断写在后面，但却是先执行的。
六、子程序
(1)、定义
子程序即执行一个特殊任务的一段分离的代码，它可以使减少重复代码且使程序易读。PERL中，子程序可以出现在程序的任何地方。定义方法为：
sub subroutine{
statements;
}
(2)、调用
调用方法如下：用&调用
&subname;
...
sub subname{
...
}