redirect action

一、将输出重定向到文件或程序.

注意：Redirect file sequence of operation is very important

> file 2>&1

将标准输出重定向到file,Then the standard error as a standard output to the same place（file）.

2>&1 > file

In contrast to the above,The standard error is redirected to standard output the default location（终端窗口,因此没有任何更改）,Only will then standard output redirectionfile.

示例

1、使用dateCommand to view the timestamp saved to/tmp/dateback中,供日后参考.

[[email protected] ~]$ date > /tmp/dateback

[[email protected] ~]$ cat /tmp/dateback
Wed  3 Aug 19:55:43 CST 2022

2、To a log file finally100Line to another file.

[[email protected] ~]$ sudo tail -n 100 /var/log/messages > /tmp/end-100

[[email protected] ~]$ wc -l /tmp/end-100
100 /tmp/end-100

3、将4A file link as1个文件.

[[email protected] log]$ sudo cat lastlog maillog tallylog > /tmp/old-log

4、Hide home directory of the file name and file name list to a file.

[[email protected] ~]$ ls -a > /tmp/my-file

5、Attach the output to the existing file.

[[email protected] ~]$ echo "new line of information" >> /tmp/many-lines
[[email protected] log]$ sudo diff lastlog tallylog >> /tmp/tracking-mode

6、When checking in on ordinary command output terminal,The error is redirected to the file.

[[email protected] ~]$ find /etc -name passwd 2> /tmp/errors
/etc/pam.d/passwd
/etc/passwd

[[email protected] ~]$ cat /tmp/errors
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/pki/pesign’: Permission denied
find: ‘/etc/ssh/sshd_config.d’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/cni/net.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/containers/networks’: Permission denied
find: ‘/etc/sos/cleaner’: Permission denied
find: ‘/etc/ipsec.d’: Permission denied
find: ‘/etc/firewalld’: Permission denied

7、Save the process output to/tmp/output文件中,To save the error message to/tmp/errors文件中.

[[email protected] ~]$ find /etc -name passwd > /tmp/output 2> /tmp/errors

[[email protected] ~]$ cat /tmp/output
/etc/pam.d/passwd
/etc/passwd

[[email protected] ~]$ cat /tmp/errors
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/pki/pesign’: Permission denied
find: ‘/etc/ssh/sshd_config.d’: Permission denied
find: ‘/etc/grub.d’: Permission denied
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/cni/net.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/containers/networks’: Permission denied
find: ‘/etc/sos/cleaner’: Permission denied
find: ‘/etc/ipsec.d’: Permission denied
find: ‘/etc/firewalld’: Permission denied

8、忽略并丢弃错误消息,But save the process output message.

[[email protected] ~]$ find /etc -name passwd > /tmp/export 2> /dev/null

[[email protected] ~]$ cat /tmp/export
/etc/pam.d/passwd
/etc/passwd

[[email protected] ~]$ cat /dev/null

9、The output and generate error messages stored together.

[[email protected] ~]$ find /etc -name passwd &> /tmp/save-both

[[email protected] ~]$ cat /tmp/save-both
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/pki/pesign’: Permission denied
find: ‘/etc/ssh/sshd_config.d’: Permission denied
/etc/pam.d/passwd
find: ‘/etc/grub.d’: Permission denied
/etc/passwd
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/cni/net.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/containers/networks’: Permission denied
find: ‘/etc/sos/cleaner’: Permission denied
find: ‘/etc/ipsec.d’: Permission denied
find: ‘/etc/firewalld’: Permission denied

10、The output and the generated error attached to an existing file.

[[email protected] ~]$ find /etc -name passwd >> /tmp/save-both 2>&1

[[email protected] ~]$ cat /tmp/save-both
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/pki/pesign’: Permission denied
find: ‘/etc/ssh/sshd_config.d’: Permission denied
/etc/pam.d/passwd
find: ‘/etc/grub.d’: Permission denied
/etc/passwd
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/cni/net.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/containers/networks’: Permission denied
find: ‘/etc/sos/cleaner’: Permission denied
find: ‘/etc/ipsec.d’: Permission denied
find: ‘/etc/firewalld’: Permission denied
find: ‘/etc/lvm/archive’: Permission denied
find: ‘/etc/lvm/backup’: Permission denied
find: ‘/etc/lvm/cache’: Permission denied
find: ‘/etc/pki/rsyslog’: Permission denied
find: ‘/etc/pki/pesign’: Permission denied
find: ‘/etc/ssh/sshd_config.d’: Permission denied
/etc/pam.d/passwd
find: ‘/etc/grub.d’: Permission denied
/etc/passwd
find: ‘/etc/sssd’: Permission denied
find: ‘/etc/polkit-1/rules.d’: Permission denied
find: ‘/etc/polkit-1/localauthority’: Permission denied
find: ‘/etc/cups/ssl’: Permission denied
find: ‘/etc/cni/net.d’: Permission denied
find: ‘/etc/nftables’: Permission denied
find: ‘/etc/audit’: Permission denied
find: ‘/etc/sudoers.d’: Permission denied
find: ‘/etc/libvirt’: Permission denied
find: ‘/etc/containers/networks’: Permission denied
find: ‘/etc/sos/cleaner’: Permission denied
find: ‘/etc/ipsec.d’: Permission denied
find: ‘/etc/firewalld’: Permission denied

二、构建管道

说明：Pipeline is a sequence of one or more orders,用竖线字符“|”分隔;Pipeline will be the first command of the standard output connected to the next command's standard input.想象一下：Data is through the pipe flow from one process to another process,Every command slightly in its flow through the pipe to do some changes.

重定向：Will send file to standard output or standard input from a file.

管道：Will be a process of standard output is sent to another process standard input.

示例

1、使用lsThe output of the command and uselessOn the terminal display output in the form of a once.

[[email protected] ~]$ ls -l /usr/bin | less

2、lsThe output of the command towc -l,Statistics from the userlsReceive the number of lines,And the bank number displayed in the end.

[[email protected] ~]$ ls | wc -l
9

3、Input in the pipe out of the current query results before10行,And the final result is redirected to a file.

[[email protected] ~]$ ls -t | head -n 10 > /tmp/ten-last
[[email protected] ~]$ cat /tmp/ten-last
rhel-8.6-x86_64-dvd.iso
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Desktop
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Pictures
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三、管道、重定向和tee命令

When redirection and pipe combination,shellWill first set the whole pipeline,And then redirect input/输出.If in the middle of the pipe using the output redirection,The output will be transferred to file,Rather than heading to the pipeline of the next command.teeOrder to overcome this limitation;在管道中,teeCopies of its standard input to its standard output,And also to standard output is redirected to the designated command parameter file.Imagine if the data flowing through a pipe of water,那么可将teeVisual into pipesT形接头,Responsible for the flow of output in both directions.

示例

1、将ls命令的输出重定向到文件,And the output to aless,So that on the terminal display in the form of one screen at a time.

[[email protected] ~]$ ls -l | tee /tmp/save-both | less

2、If at the end of pipe to usetee,You can save the final output of the command and output to the terminal at the same time.

[[email protected] ~]$ ls -t | head -n 10 | tee /tmp/ten-lest
rhel-8.6-x86_64-dvd.iso
Downloads
Desktop
Documents
Music
Pictures
Public
Templates
Videos
[[email protected] ~]$ cat /tmp/ten-lest
rhel-8.6-x86_64-dvd.iso
Downloads
Desktop
Documents
Music
Pictures
Public
Templates
Videos