Getting Started with Linux Basics--io redirects and pipelines

IO Redirection and piping

Always mentioned, program: Instruction + data

In fact, the program also has IO, the source of data has many places: file, external

Devices available for input: Files (all Linux files)

Keyboard device, file system on the regular file loading content, network card, etc.;

Devices available for output: Files (all Linux files)

Monitor, file system on the regular file output save, network card, etc.;

There are three types of data flow in the program:

input data stream; <--standard input (stdin), is the keyboard;

Output data Flow:--> standard output (stdout), display;

Error output stream:--Error output (stderr), display;

Fd:file descriptor, file descriptor; the corresponding identifier is as follows:

Standard input: 0

Standard output: 1

Error Output: 2

IO redirection:

output redirection:>

Features: Overwrite output, overwrite anaconda-ks.cfg file contents into Kk.txt

[Email protected]_1 ~]# cat anaconda-ks.cfg > Kk.txt

output redirection:>>

Features: Append output, add from tail of file

[Email protected]_1 ~]# cat anaconda-ks.cfg >> kk.txt

Error Output stream redirection:2>,2>> (Append)

[Email protected]_1 sh]# cat Test.txt 2> Error.log

[Email protected]_1 sh]# Cat Error.log

Cat:test.txt:No such file or directory

[Email protected]_1 sh]# cat Test.log 2>> Error.log

[Email protected]_1 sh]# Cat Error.log

Cat:test.txt:No such file or directory

Cat:test.log:No such file or directory

merge Normal output stream and error output stream:

The merge output stream also has two ways of overwriting and appending:

(1) &>, &>>

(2) COMMAND >/path/to/somefile 2>&1

COMMAND >>/path/to/somefile 2>&1

[Email protected] tmp]# cat/root/anaconda-ks.cfg >> an.cfg 2>&1

Note : Viewing the contents of the Anaconda-ks.cfg file is appended to the an.cfg, and if an error output is appended to the An.cfg file;

Mention Special equipment:/dev/null

This special device is understood as a "data black hole", and all data thrown in it will be deleted.

Set is shell internal command, you can set prohibit overwrite output redirect to existing file; (Centos 6)

[Email protected] ~]# set-c

[email protected] ~]# Cat fstab > issue

-bash:issue:cannot Overwrite existing file

If you cannot use the redirection feature when it is turned on, you can use the force overwrite output at this time: >|:

[email protected] ~]# cat Fstab >| Issue

Turn off these features:

[Email protected] ~]# set-c

Note: Set settings are only valid for the current shell

input Redirect:<

Input redirection is the data input source for the command, which does some work on the data.

Let's start with a command:

TR command:

Tr-translate or delete characters

Format:

TR [OPTION] ... SET1 [SET2]

Converts the characters in the input data to all occurrences within the SET1 definition, with all one by one pairs of bits converted to SET2 characters

Options:

-D: Deleting a character Set

Example 1:

TR SET1 SET2 </path/from/somefile

[Email protected]_1 sh]# TR s S </issue

\s

Kernel \ r on an \m

NOTE: Convert all uppercase s in issue to lowercase s

Example 2:

Tr-d SET1 </path/from/somefile

[Email protected]_1 sh]# tr-d S <./issue

\

Kernel \ r on an \m

Note: Do not modify the original file

here document (created here):<<

Terminator Operation two ways:

Cat << EOF

Cat >/path/to/somefile << EOF

Example:

[[Email protected]_1 sh]# Cat << EOF

> Hello

> EOF

Hello

Explain:

EOF is a terminator that exits when there is EOF in the input content

Pipeline:

A connection program that implements the output of the previous command directly after a program as an input data stream

Can be multi-level connection:

COMMAND1 | COMMAND2 | COMMAND3 | ...

Pipe symbol: |

[[Email protected]_1 sh]# cat/etc/issue | TR Cos cos

Tee command:

Bidirectional pipeline, meaning that the input data stream is retained and a program is used as the input data stream in the secondary

Format:

COMMAND | Tee/path/to/somefile

Example:

[Email protected] ~]# Cat/etc/issue | Tee KKK | Tr-d ' 6.4 '

CentOS Release (Final)

Kernel \ r on an \m

[email protected] ~]# cat KKK

CentOS Release 6.4 (Final)

Kernel \ r on an \m

Exercise 1: Convert the information from the first 6 lines of the/etc/passwd file into uppercase characters after output;

[Email protected] ~]# Head-n 6/etc/passwd | Tr ' A-Z ' A-Z

This article is from the "Disguised Geek" blog, please be sure to keep this source http://waldenkk.blog.51cto.com/2410270/1929948

Getting Started with Linux Basics--io redirects and pipelines