1:查看本系统shell的默认交互shell
yusuwudeMacBook-Pro:~ yusuwu$ cat /etc/passwd nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false root:*:0:0:System Administrator:/var/root:/bin/sh daemon:*:1:1:System Services:/var/root:/usr/bin/false
2:查看本系统的shell
yusuwudeMacBook-Pro:~ yusuwu$ ls -lF /bin/*sh -r-xr-xr-x 1 root wheel 623472 4 7 03:52 /bin/bash* -rwxr-xr-x 1 root wheel 529424 4 7 03:52 /bin/csh* -rwxr-xr-x 1 root wheel 110848 4 7 03:52 /bin/dash* -r-xr-xr-x 1 root wheel 1300256 4 7 03:52 /bin/ksh* -rwxr-xr-x 1 root wheel 31440 4 7 03:52 /bin/sh* -rwxr-xr-x 1 root wheel 529424 4 7 03:52 /bin/tcsh* -rwxr-xr-x 1 root wheel 637632 4 7 03:52 /bin/zsh*
通过上面命令执行结果来看,*sh都是可执行程序,如果我们想切入到其他的shell,可以直接执行命令:
yusuwudeMacBook-Pro:~ yusuwu$ /bin/bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ exit exit yusuwudeMacBook-Pro:~ yusuwu$
退出exit则可.
3:shell的父子关系
yusuwudeMacBook-Pro:~ yusuwu$ ps -f UID PID PPID C STIME TTY TIME CMD 501 1457 1456 0 6:17下午 ttys000 0:00.02 -bash yusuwudeMacBook-Pro:~ yusuwu$ /bin/bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ ps -f UID PID PPID C STIME TTY TIME CMD 501 1457 1456 0 6:17下午 ttys000 0:00.02 -bash 501 1844 1457 0 11:20下午 ttys000 0:00.01 /bin/bash bash-3.2$ /bin/dash $ ps -f UID PID PPID C STIME TTY TIME CMD 501 1457 1456 0 6:17下午 ttys000 0:00.02 -bash 501 1844 1457 0 11:20下午 ttys000 0:00.01 /bin/bash 501 1846 1844 0 11:20下午 ttys000 0:00.00 /bin/dash $ exit bash-3.2$ exit exit yusuwudeMacBook-Pro:~ yusuwu$
通过上面代码的执行顺序和父子的PID可以看出.
3.1:进程列表
命令列表只需要在命令之间加分号“;”即可,命令列表想成为进程列表,这些命令就必须加在园括号里.
yusuwudeMacBook-Pro:~ yusuwu$ pwd;cd /etc/;pwd;cd ;ls;echo $BASH_SUBSHELL /Users/yusuwu /etc Applications Movies YXL.tar Applications (Parallels) Music eclipse-workspace-20200505 Desktop Parallels iCloud Drive（归档） Documents Pictures jetbrains-agent Downloads Postman package-lock.json IdeaProjects Public resourceFiles Library YXL 0 yusuwudeMacBook-Pro:~ yusuwu$ (pwd;cd /etc/;pwd;cd;ls;echo $BASH_SUBSHELL ); /Users/yusuwu /etc Applications Movies YXL.tar Applications (Parallels) Music eclipse-workspace-20200505 Desktop Parallels iCloud Drive（归档） Documents Pictures jetbrains-agent Downloads Postman package-lock.json IdeaProjects Public resourceFiles Library YXL 1 yusuwudeMacBook-Pro:~ yusuwu$
住: echo $BASH_SUBSHELL 如果这个命令返回0,就表示没有子sehll,如果返回1或者其他更大的数字,就表示存在子shell.上面执行的代码可以看出被园括号括住的命令列表变成了进程列表,
进程列表会生成一个子shell来执行对应的命令.
3.2:后台模式:
要想将命令置入后台模式,可以在命令末尾加上字符&;
yusuwudeMacBook-Pro:~ yusuwu$ sleep 10 yusuwudeMacBook-Pro:~ yusuwu$ ps -f UID PID PPID C STIME TTY TIME CMD 501 1457 1456 0 6:17下午 ttys000 0:00.06 -bash yusuwudeMacBook-Pro:~ yusuwu$ sleep 20& [1] 1871 yusuwudeMacBook-Pro:~ yusuwu$ ps -f UID PID PPID C STIME TTY TIME CMD 501 1457 1456 0 6:17下午 ttys000 0:00.07 -bash 501 1871 1457 0 11:34下午 ttys000 0:00.00 sleep 20 yusuwudeMacBook-Pro:~ yusuwu$ jobs [1]+ Running sleep 20 & yusuwudeMacBook-Pro:~ yusuwu$ jobs -l [1]+ 1871 Done sleep 20
3.3:将进程列表置入后台:
yusuwudeMacBook-Pro:~ yusuwu$ (sleep 10; echo $BASH_SUBSHELL ; sleep 10)& [1] 1876
在CLI中运用子shell出创造性方法之一就是将进程列表置入后台模式,这样我们既可以在子shell中进行繁重的处理工作,同时也不会让子shell的I/O受制于终端.
eg:
yusuwudeMacBook-Pro:~ yusuwu$ (tar -czf ./YXL.tar.gz ./YXL)& [1] 1888
当然将进程列表置入后台模式并不是子shell在CLI中仅有的创造性用法.协程就是另一种方法.
3.4:协程
协程可以同时做两件事,它在后台生成一个子shell,并在这个子shell中执行命令.要进行协程处理,得使用coproc命令,还有要在子shell中执行的命令.
$ coproc sleep 10
[1] 2544
$
除了会创建在shell外,协程基本上就是将命令置入后台模式.
$ jobs
[1]+ Running coproc COPROC sleep 10 &
$
COPROC是coproc命令给进程起的名字,我们也可以使用命令的扩展语法自己设置这个名字
$ coproc my_job { sleep 10; }
[1] 2570
$
$jobs
[1]+ Running coproc my_job { sleep 10; } &
$
这里要注意的是:扩展语法写起来必须要确保在第一个花括号"{"和命令之间有一个空格.还必须保证命令以分号";"结尾,另外分号和闭花括号"}"之间也得有一个空格.
4:理解shell的内建命令
4.1:外部命令和内建命令的区分
yusuwudeMacBook-Pro:bin yusuwu$ type -a ps ps is /bin/ps yusuwudeMacBook-Pro:bin yusuwu$ which ps /bin/ps yusuwudeMacBook-Pro:bin yusuwu$ type -a pwd pwd is a shell builtin pwd is /bin/pwd yusuwudeMacBook-Pro:bin yusuwu$ type pwd pwd is a shell builtin yusuwudeMacBook-Pro:bin yusuwu$ which pwd /bin/pwd yusuwudeMacBook-Pro:bin yusuwu$ type -a echo echo is a shell builtin echo is /bin/echo yusuwudeMacBook-Pro:bin yusuwu$
外部命令也被称为文件系统命令.是存在于bash shell之外的程序.它们并不是shell程序的一部分,外部命令程序通常位于/bin,/usr/bin,/sbin或/usr/sbin中.
当外部命令执行时会衍生的创建出一个子进程,当进程必须执行衍生操作时,它需要花费时间和精力来设置新子进程的环境,所以说,外部命令多少还是有代价的.
内建命令和外部命令的区别在于前者不需要使用子进程来执行,它们已经和shell编译成了一体,作为shell工具的组成部分存在.不需要借助外部程序文件来运行.
所以内建命令的执行效率更高.
yusuwudeMacBook-Pro:bin yusuwu$ type -a exit exit is a shell builtin
命令type -a显示出每个命令的两种实现,which命令只显示了外部命令文件.
[1]:history
yusuwudeMacBook-Pro:bin yusuwu$ type -a history history is a shell builtin yusuwudeMacBook-Pro:bin yusuwu$ history ... 111 ls 112 cd JavaVirtualMachines/ ... 609 type -a history 610 history
记: !! 加回车:执行刚才执行的一条命令
!加命令编号: eg: !112 则会执行history中的112条命令.
history -a和history -n命令用法
[2]:命令别名 alias
yusuwudeMacBook-Pro:~ yusuwu$ la -bash: la: command not found yusuwudeMacBook-Pro:~ yusuwu$ alias la='ls -al' yusuwudeMacBook-Pro:~ yusuwu$ la total 721400 drwxr-xr-x+ 50 yusuwu staff 1600 5 16 00:22 . drwxr-xr-x 6 root admin 192 4 7 03:45 .. -r-------- 1 yusuwu staff 9 6 19 2018 .CFUserTextEncoding -rw-r--r--@ 1 yusuwu staff 24580 5 13 16:26 .DS_Store
