The “$?” is a built-in variable that your shell uses to store the exit status code of the last executed command in integer format and remains unchanged unless the next command is executed. Using this exit status code, you can debug the problem that occurred while executing the command, ...
Exit codes can be interpreted by machine scripts to adapt in the event of successes of failures. If exit codes are not set the exit code will be the exit code of the last run command. How to get the exit code of a command¶
(If n is omitted, the exit status is that of the last command executed. ) 格式:$? 上一个命令的退出码。 格式:trap "commands" EXIT 退出时执行commands指定的命令。( A trap on EXIT is executed before the shell terminates.) 退出码(exit status,或exit code)的约定: 0表示成功(Zero - Success...
other similar circumstances include when you want to pass a * character to a command such as grep instead of having the shell expand it, and when you need to need to use a
68//执行命令69voidExecuteCommand()70{//创建子进程71pid_t id=fork();72if(id==0)73{//进程替换74execvp(gArgv[0],gArgv);75exit(errno);76}77else78{79int status=0;80pid_t rid=waitpid(id,&status,0);//进程等待81if(rid>0)82{//如果错误打印错误信息83int lastcode=WEXITSTATUS(status)...
last command's log report lvchange Change the attributes of logical volume(s) lvconvert Change logical volume layout lvcreate Create a logical volume lvdisplay Display information about a logical volume lvextend Add space to a logical volume lvmchange With the device mapper, this is obsolete and ...
Every function in shell scripting returns some value, the dafault return value is the exit code/status code of the last command inside function. But based on our requirement, we can return values explicitly by using the return statement return <exit_code>, the allowed values are in the range...
Again, the error message points to a error that occurs later than the actual problem. What happens is really pretty interesting. As we recall, if accepts a list of commands and evaluates the exit code of the last command in the list. In our program, we intend this list to consist of ...
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{return3;}cout<<"wait child success:"<<ret<<",exitcode:"<<((status>>8)&0xFF)<<",signlcode:"<<(status&0x7F)<<endl;sleep(5);cout<<"father quit "<<endl;return0;} 管道的五大特性 匿名管道是具有血缘关系的进程间进行通信。 只能进行单向通信...