1、什么是输入输出
在linux系统中，0表示为标准输入，1表示为标准输出，2表示为错误输出。
上图中，键盘为标准输入也就是编号0，而标准输出1和标准错误2都可以显示在显示屏上。
运行一个程序时 , 需要从某个位置读取输入信息 , 然后 cpu 处理, 最后将输出显示到屏幕或文件进程通过文件描述符的编号通道来获取输入并输出。
2、输出重定向
1>
重定向正确输出
利用root用户在/etc目录下查询passwd文件：将查询的正确结果保存在file文件中，使用cat查询。
[root@foundation50 Desktop]# find /etc/ -name passwd > file
[root@foundation50 Desktop]# cat file
/etc/pam.d/passwd
/etc/passwd
2>
重定向错误输出
利用root用户在/etc目录下查询passwd文件：将查询的错误结果保存在file1文件中，使用cat查询，没有！。
利用普通用户在/etc目录下查询passwd文件：将查询的错误结果保存在file2文件中，使用cat查询。
[root@foundation50 Desktop]# su -- westos
[westos@foundation50 Desktop]$ find /etc -name passwd
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
[westos@foundation50 Desktop]$ find /etc -name passwd 2> file2 把错误输出存到副ile2
/etc/pam.d/passwd
/etc/passwd
[westos@foundation50 Desktop]$ cat file2
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
&>
重定向所有输出
在/etc目录下查询passwd文件：将查询的所有结果保存在file3文件中，使用cat查询
[westos@foundation50 Desktop]$ find /etc -name passwd &> file3
[westos@foundation50 Desktop]$ cat file3
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
利用重定向清空文件
[westos@foundation50 Desktop]$ > file3
[westos@foundation50 Desktop]$ cat file3
[westos@foundation50 Desktop]$
输出正确的追加，原内容不会被清空
[westos@foundation50 Desktop]$ cat file3 原文件
/etc/pam.d/passwd
/etc/passwd
[westos@foundation50 Desktop]$ find /etc -name passwd >> file3
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
[westos@foundation50 Desktop]$ cat file3
/etc/pam.d/passwd
/etc/passwd
/etc/pam.d/passwd
/etc/passwd
2>> 追加错误输出
[westos@foundation50 Desktop]$ cat file3 原文件
/etc/pam.d/passwd
/etc/passwd
[westos@foundation50 Desktop]$ find /etc -name passwd 2>> file3
/etc/pam.d/passwd
/etc/passwd
[westos@foundation50 Desktop]$ cat file3
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
&>>
追加所有输出到文件最后
[westos@foundation50 Desktop]$ cat file3
[westos@foundation50 Desktop]$ find /etc -name passwd &>> file3
[westos@foundation50 Desktop]$ cat file3
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
输出重定向会覆盖文件内容，追加重定向不会覆盖文件原来的内容
| 管道
"|"管道的作用是把前一条命令的正确输出变成后一条命令的输入
通过管道的输出将会变成输入，会被第二条命令处理
[westos@foundation50 Desktop]$ find /etc -name passwd | wc -l 正确的输出会被管道符通过，错误的不会通过
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
2
如果让错误的输出也要被管道符通过，则需要把错误的输出追加到正确的输出里 2>&1
[westos@foundation50 Desktop]$ find /etc -name passwd 2>&1 | wc -l
17
若需要将输出内容保存一份，可以通过tee 复制两份，一份保存到文件里，一份通过管道让wc -l 来处理
[westos@foundation50 Desktop]$ find /etc -name passwd 2>&1 |tee file1 | wc -l
17
[westos@foundation50 Desktop]$ cat file1
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
3 、输入重定向
<
[root@foundation50 Desktop]# cat test
hello
HELLO
[root@foundation50 Desktop]# tr 'a-z' 'A-Z' < test 将shell的0（输入)定向到tr 程序的0里面，因为shell不具备转换大小写的功能
HELLO
HELLO
<<
多行输入重定向
vim westos.sh
date
passwd root << EOF << 表示多行输入 EOF 表示起始字符串
westos
westos
EOF 遇到EOF j结束
[root@foundation50 Desktop]# sh westos.sh 运行
Wed Aug 4 21:50:50 CST 2021
Changing password for user root.
New password: BAD PASSWORD: The password is shorter than 8 characters
Retype new password: passwd: all authentication tokens updated successfully.
练习：
4、[westos@foundation50 Desktop]$ find /etc -name passwd 2>&1 | tee /dev/pts/0 | wc -l #/dev/pts/o 放入字符设备，能显示出来的就叫字符设备
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/dhcp’: Permission denied
/etc/pam.d/passwd
/etc/passwd
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
17
5、[westos@foundation50 Desktop]$ tr 'a-z' 'A-Z' < /etc/passwd | cat -n
1 ROOT:X:0:0:ROOT:/ROOT:/BIN/BASH
2 BIN:X:1:1:BIN:/BIN:/SBIN/NOLOGIN
3 DAEMON:X:2:2:DAEMON:/SBIN:/SBIN/NOLOGIN
4 ADM:X:3:4:ADM:/VAR/ADM:/SBIN/NOLOGIN
5 LP:X:4:7:LP:/VAR/SPOOL/LPD:/SBIN/NOLOGIN
6 SYNC:X:5:0:SYNC:/SBIN:/BIN/SYNC
7 SHUTDOWN:X:6:0:SHUTDOWN:/SBIN:/SBIN/SHUTDOWN
8 HALT:X:7:0:HALT:/SBIN:/SBIN/HALT
9 MAIL:X:8:12:MAIL:/VAR/SPOOL/MAIL:/SBIN/NOLOGIN
10 OPERATOR:X:11:0:OPERATOR:/ROOT:/SBIN/NOLOGIN
11 GAMES:X:12:100:GAMES:/USR/GAMES:/SBIN/NOLOGIN
12 FTP:X:14:50:FTP USER:/VAR/FTP:/SBIN/NOLOGIN
13 NOBODY:X:65534:65534:KERNEL OVERFLOW USER:/:/SBIN/NOLOGIN
14 DBUS:X:81:81:SYSTEM MESSAGE BUS:/:/SBIN/NOLOGIN
15 SYSTEMD-COREDUMP:X:999:997:SYSTEMD CORE DUMPER:/:/SBIN/NOLOGIN
16 SYSTEMD-RESOLVE:X:193:193:SYSTEMD RESOLVER:/:/SBIN/NOLOGIN
17 TSS:X:59:59:ACCOUNT USED BY THE TROUSERS PACKAGE TO SANDBOX THE TCSD DAEMON:/DEV/NULL:/SBIN/NOLOGIN
18 POLKITD:X:998:996:USER FOR POLKITD:/:/SBIN/NOLOGIN
19 GEOCLUE:X:997:995:USER FOR GEOCLUE:/VAR/LIB/GEOCLUE:/SBIN/NOLOGIN
20 RTKIT:X:172:172:REALTIMEKIT:/PROC:/SBIN/NOLOGIN
21 PIPEWIRE:X:996:994:PIPEWIRE SYSTEM DAEMON:/VAR/RUN/PIPEWIRE:/SBIN/NOLOGIN
22 PULSE:X:171:171:PULSEAUDIO SYSTEM DAEMON:/VAR/RUN/PULSE:/SBIN/NOLOGIN
23 LIBSTORAGEMGMT:X:995:991:DAEMON ACCOUNT FOR LIBSTORAGEMGMT:/VAR/RUN/LSM:/SBIN/NOLOGIN
24 QEMU:X:107:107:QEMU USER:/:/SBIN/NOLOGIN
25 USBMUXD:X:113:113:USBMUXD USER:/:/SBIN/NOLOGIN
26 UNBOUND:X:994:989:UNBOUND DNS RESOLVER:/ETC/UNBOUND:/SBIN/NOLOGIN
27 RPC:X:32:32:RPCBIND DAEMON:/VAR/LIB/RPCBIND:/SBIN/NOLOGIN
28 GLUSTER:X:993:988:GLUSTERFS DAEMONS:/RUN/GLUSTER:/SBIN/NOLOGIN
29 CHRONY:X:992:987::/VAR/LIB/CHRONY:/SBIN/NOLOGIN
30 SETROUBLESHOOT:X:991:985::/VAR/LIB/SETROUBLESHOOT:/SBIN/NOLOGIN
31 SASLAUTH:X:990:76:SASLAUTHD USER:/RUN/SASLAUTHD:/SBIN/NOLOGIN
32 DNSMASQ:X:984:984:DNSMASQ DHCP AND DNS SERVER:/VAR/LIB/DNSMASQ:/SBIN/NOLOGIN
33 RADVD:X:75:75:RADVD USER:/:/SBIN/NOLOGIN
34 CLEVIS:X:983:982:CLEVIS DECRYPTION FRAMEWORK UNPRIVILEGED USER:/VAR/CACHE/CLEVIS:/SBIN/NOLOGIN
35 COCKPIT-WS:X:982:980:USER FOR COCKPIT WEB SERVICE:/NONEXISTING:/SBIN/NOLOGIN
36 COCKPIT-WSINSTANCE:X:981:979:USER FOR COCKPIT-WS INSTANCES:/NONEXISTING:/SBIN/NOLOGIN
37 SSSD:X:980:978:USER FOR SSSD:/:/SBIN/NOLOGIN
38 FLATPAK:X:979:977:USER FOR FLATPAK SYSTEM HELPER:/:/SBIN/NOLOGIN
39 COLORD:X:978:976:USER FOR COLORD:/VAR/LIB/COLORD:/SBIN/NOLOGIN
40 GDM:X:42:42::/VAR/LIB/GDM:/SBIN/NOLOGIN
41 RPCUSER:X:29:29:RPC SERVICE USER:/VAR/LIB/NFS:/SBIN/NOLOGIN
42 GNOME-INITIAL-SETUP:X:977:975::/RUN/GNOME-INITIAL-SETUP/:/SBIN/NOLOGIN
43 SSHD:X:74:74:PRIVILEGE-SEPARATED SSH:/VAR/EMPTY/SSHD:/SBIN/NOLOGIN
44 AVAHI:X:70:70:AVAHI MDNS/DNS-SD STACK:/VAR/RUN/AVAHI-DAEMON:/SBIN/NOLOGIN
45 RNGD:X:976:974:RANDOM NUMBER GENERATOR DAEMON:/VAR/LIB/RNGD:/SBIN/NOLOGIN
46 TCPDUMP:X:72:72::/:/SBIN/NOLOGIN
47 WESTOS:X:1000:1000::/HOME/WESTOS:/BIN/BASH
48 APACHE:X:48:48:APACHE:/USR/SHARE/HTTPD:/SBIN/NOLOGIN
7、cat > westos.file << EOF
hello linux
hello westos
hello linux
westos linux is very nice
EOF
1、[westos@foundation50 Desktop]$ find /etc -name passwd 2> /dev/null
/etc/pam.d/passwd
/etc/passwd
内容补充
若让文件内容倒则显示 使用tac 命令
[root@foundation50 Desktop]# cat test
1
2
3
4
[root@foundation50 Desktop]# tac test
4
3
2
1