Input and output in Linux
Input
stdin [standard input stream ]
input system refers to the system information transmitted to the external
of a system external to the data transmission system is as follows
1. Keyboard
2. Mouse
3. Enter the command
output
| Export | as standout [Standard correctly entered] | stderr [standard error] |
|---|---|---|
| In the string of commands executed successfully completed | Command string generated by the failure to complete execution | |
| Output signal is 1 linux | stderr output signal in the linux 2 |
Character device
Character device refers to the character units of transmission devices in I / O transfer process, such as a keyboard, a printer,
a character memory device is a virtual device opened and real
Redirect the output find / etc / -name passwd
Note: You must under ordinary users
| 1> | 2> | &> |
|---|---|---|
| Correct output | Error output | All output |
Applet:> westos Empty file
2 find / etc / -name passwd added: do not overwrite the original file
find / etc / -name passwd> westos.out correct output is stored in the westos.out
add to
Additional right / wrong / all
pipeline
Channel definitions: the output becomes the input of the last command
| symbol | use |
|---|---|
| 2>&1 | Converting the output of No. 1 of 2 |
| lee | Copy output to the specified position |
| ‘ | 'Pipe symbol |
Example: 3 to 5 show the history of output lines
[student@workstation Desktop]$ ls /bin | wc -l ##统计/bin有多少文件
1612
[student@workstation Desktop]$ find /etc/ -name passwd | wc -l ##默认只有正确输出可以通过管道
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
2
[student@workstation Desktop]$ find /etc/ -name passwd 2>&1 | wc -l ##将错误输出定向到正确输出存放位置
16
[student@workstation Desktop]$ find /etc/ -name passwd | tee file | wc -l #复制输出到file文件再通过管道统计
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/lvm/archive’: Permission-
** input redirection
To modify the password, for example
Input redirection symbol
command << [输入标识]
内容
...
...
[输入标识]More convenient, do not have to enter a password, direct editing in vim
1. vim editing westos.sh file. The passwd direct input, a password is required to change the password at
2. input redirection symbols, it is more convenient to directly edit
-