Perl process management
You can create processes in different ways in Perl.
This tutorial will discuss some process management methods.
You can use the special variable $$ or $PROCESS_ID to get the process ID.
%ENV hash stores the parent process, which is the environment variables in the shell. These variables can be modified in Perl.
exit() is usually used to exit a child process. The main process exits after all child processes have exited.
All open handles will be copied by the dup() function in the subroutine, and closing all handles of the process will not affect other processes.
Backtick operator
Using the backtick operator makes it easy to execute Unix commands. You can insert some simple commands in backticks. After the command is executed, the result will be returned:
#!/usr/bin/perl
@files = `ls -l`;
foreach $file (@files){
print $file;
}
1;Execute the above program, the output result is as follows:
drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14 drwxr-xr-x 4 root root 4096 Sep 13 07:54 android -rw-r--r-- 1 root root 574 Sep 17 15:16 index.htm drwxr-xr-x 3 544 401 4096 Jul 6 16:49 MIME-Lite-3.01 -rw-r--r-- 1 root root 71 Sep 17 15:16 test.pl ……
system() function
You can also use system () The function executes a Unix command, and executing the command will directly output the result. By default, it will be sent to the place where Perl's STDOUT currently points, which is usually the screen. You can also use the redirection operator> to output to a specified file:
Execute the above program, the output result is as follows:
drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14 drwxr-xr-x 4 root root 4096 Sep 13 07:54 android -rw-r--r-- 1 root root 574 Sep 17 15:16 index.htm drwxr-xr-x 3 544 401 4096 Jul 6 16:49 MIME-Lite-3.01 -rw-r--r-- 1 root root 71 Sep 17 15:16 test.pl ……
You need to note that the command contains environment variables such as $PATH or $HOME The output result is as follows:
#!/usr/bin/perl
$PATH = "我是 Perl 的变量";
system('echo $PATH'); # $PATH 作为 shell 环境变量
system("echo $PATH"); # $PATH 作为 Perl 的变量
system("echo $PATH"); # 转义 $
1;Execute the above program and the output result is as follows:
/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin 我是 Perl 的变量 /usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin
fork() function
Perl fork() function is used to create a new process.
Returns the PID of the child process in the parent process, and returns 0 in the child process. If an error occurs (for example, insufficient memory), undef is returned and $! is set to the corresponding error message.
fork can be used in conjunction with exec. The process ends after the exec function executes the command in quotes.
#!/usr/bin/perl
if(!defined($pid = fork())) {
# fork 发生错误返回 undef
die "无法创建子进程: $!";
}elsif ($pid == 0) {
print "通过子进程输出\n";
exec("date") || die "无法输出日期: $!";
} else {
# 在父进程中
print "通过父进程输出\n";
$ret = waitpid($pid, 0);
print "完成的进程ID: $ret\n";
}
1;Execute the above program, the output result is as follows:
通过父进程输出 通过子进程输出 2016年 6月19日 星期日 22时21分14秒 CST 完成的进程ID: 47117
If the process exits, it will send a CHLD signal to the parent process, and it will become a zombie process, which needs to be used by the parent process. wait and waitpid to terminate. Of course, you can also set $SIG{CHLD} to IGNORG:
#!/usr/bin/perl
local $SIG{CHLD} = "IGNORE";
if(!defined($pid = fork())) {
# fork 发生错误返回 undef
die "无法创建子进程: $!";
}elsif ($pid == 0) {
print "通过子进程输出\n";
exec("date") || die "无法输出日期: $!";
} else {
# 在父进程中
print "通过父进程输出\n";
$ret = waitpid($pid, 0);
print "完成的进程ID: $ret\n";
}
1;Execute the above program, the output result is as follows:
通过父进程输出 通过子进程输出 2016年 6月19日 星期日 22时30分56秒 CST 完成的进程ID: -1
Kill function
Perl kill('signal', (Process List))Send a signal to a group of processes. signal is the digital signal sent, 9 is to kill the process.
First take a look at the commonly used signals in Linux, see the following list:
信号名 值 标注 解释 ———————————————————————————————————————————————————————————— HUP 1 A 检测到挂起 INT 2 A 来自键盘的中断 QUIT 3 A 来自键盘的停止 ILL 4 A 非法指令 ABRT 6 C 失败 FPE 8 C 浮点异常 KILL 9 AF 终端信号 USR1 10 A 用户定义的信号1 SEGV 11 C 非法内存访问 USR2 12 A 用户定义的信号2 PIPE 13 A 写往没有读取者的管道 ALRM 14 A 来自闹钟的定时器信号 TERM 15 A 终端信号 CHLD 17 B 子进程终止 CONT 18 E 如果被停止则继续 STOP 19 DF 停止进程 TSTP 20 D tty键入的停止命令 TTIN 21 D 对后台进程的tty输入 TTOU 22 D 对后台进程的tty输出
The following examples send SIGINT signals to processes 104 and 102:
#!/usr/bin/perl
kill('INT', 104, 102);
1;
