4. Bash basics and configurations, standard I/O, pipelines, and shell programming basics;

Labels: Bash basics and standard I/O pipeline shell programming Basics

1. Bash basics and configurations

From the user's perspective, the shell type:

Logon Shell

Log On Through a terminal normally

Su-Username

Su-l Username

Non-Logon Shell

Su Username

Virtual terminal opened under the graphic Terminal

Automatically executed shell script

Bash configuration file:

Global Configuration:

/Etc/profile,/etc/profile. d/*. Sh,/etc/bashrc

Personal Configuration:

~ /. Bash_profile ,~ /. Bashrc

Profile files

1. Set Environment Variables

2. run commands or scripts

Bashrc files

1. Define local variables

2. Define command alias

How to read the configuration file using a logon shell:

/Etc/profile ---->/etc/profile. d/*. Sh ----> ~ /. Bash_profile ---->/etc/bashrc

How does a non-Logon shell read the configuration file:

~ /. Bashrc --->/etc/bashrc ---->/etc/profile. d/*. Sh

Completely switch between Su-username and Su-l Username

Semi-switching: su Username

The smaller the scope, the more effective it will be.

How to configure a permanent alias command? Personal? Global?

How to configure a permanent global prompt? Personal? Global?

2. Pipelines and IO redirection

Host, controller ----> CPU

Memory: Ram

Input/output devices

 

Program: Command + Data

 

Controller: Command

Timer:

Memory:

 

Address Bus: memory addressing

Data Bus: Data Transmission

Control Bus: control commands

Actually, it is a bus with three functions

Register: CPU temporary memory

I/O: hard disk,

Program:

Input device:

Output device:

System settings:

Default output device: standard output, stdout, 1

Default Input Device: standard input, stdin, 0

Default error output: standard error, stderr, 2

Standard Input Device: keyboard

Standard output and error output: Display (cheap)

I/O redirection:

Linux

Output redirection (greater than the number):> overwrite the output

> Append output

Set-C prohibits overwrite redirection for existing files

To forcibly overwrite the output, use> |

Set + C disable the above functions

2> redirect error output

2> append Mode

&>: Redirects standard output or error output to the same file, overwriting

Input redirection (minor sign): <

<Here document generates the document Terminator: end, EOF

 

 

Pipeline: Use the output of the previous command as the input of the next command.

Command 1 | command 2 | command 3 | ....

Exercise:

1. count the number of files in the/usr/bin/directory;

Ls/usr/bin/| WC-l

2. Retrieve the shells of all users on the current system. Each shell is only displayed once and displayed in order;

Cut-D:-F 7/etc/passwd | sort-u

3. Thinking: how to display the content types of each file in the/var/log directory?

4. Extract the 6th rows of the/etc/inittab file;

5. Retrieve the username and shell of the last 9th users in the/etc/passwd file, display them on the screen, and save them to the/tmp/users file;

Cut-D:-F 1,7/etc/passwd | head-9 | tail-1 | tee/tmp/users

6. display all files starting with PA in the/etc directory and count the number of files;

7. If you do not use a text editor, add a line of Alias CLS = clear content to the. bashrc file of the current user;

Regular Expression:

Text Search needs:

Grep, egrep, fgrep

Grep: searches for text based on the mode, and displays the line of conforming text to the screen.

Pattern: A match condition composed of text characters and metacharacters of Regular Expressions

Grep [Options] pattern [file...]

-I (Case Insensitive)

-- Color [matching character display color]

-V: displays the rows not matched by the pattern.

-O only displays the strings matched by the pattern

*: Any character of any length

? : Any single character

[]:

[^]

Regular Expression: Regular Expression, Regexp

Metacharacters:

.: Match any single character

[]: Match a single character in a specified range

[^]: Match a single character out of the specified range

Character Set combination: [: digit:], [: lower:], [: Upper:], [: punct:], [: Space:], [: Alpha:], [: alnum:]

Matching times: (Greedy mode, matching as long as possible)

*: Match any character before it.

A, B, AB, AAB, ACB, ADB, amnb

A * B (indicating any times a, followed by B): AB, AAB

A. * B only needs to start with a and end with B.

A \? B:

. *: Any character of any length

\? : Match the first character once or 0

\ {M, N \}: match the first character at least m times, at most N times

\ {1, \}: at least once

\ {0, 3 \}: up to 3 times

Positioning:

^: Specifies the beginning of a line. Any content after this character must appear at the beginning of the line.

$: Pin the end of a line: any content after this character must appear at the end of a line

^ $: Blank line;

The start of the anchor word \ <or \ B: Any character after it must be used as the header of the word. For example, Root \ B or Root \ <

The anchor at the end of a word \> or \ B: Any character before it must be used as the end of the word to show eg: \ broot or \> root

Word: starts with a letter and ends with no special characters in the middle. r55t

GROUP:

\(\)

\ (AB \)*

Backward reference

\ 1: reference the first left brace and all content contained in the corresponding right Brace

\ 2:

\ 3:

Exercise:

1. display the lines starting with "S" of the/proc/meminfo file with no size difference;

Grep-I '^ s'/proc/meminfo

Grep '^ [ss]'/proc/meminfo

2. display the rows ending with nologin in/etc/passwd;

Grep 'nologin $ '/etc/passwd

Retrieve the list of users whose default shell is/sbin/nologin.

Grep "nologin $ '/etc/passwd | cut-D:-F1

Obtain the username of the user whose default shell is Bash and whose user ID is the smallest

Grep 'bash $ '/etc/passwd | sort-n-t:-K3 | head-1 | cut-D:-F1

3. the/etc/inittab starts with #, followed by one or more blank characters, and then followed by any non-blank lines;

Grep "^ # [[: Space:] \ {1, \} [^ [: Space:]"/etc/inittab

4. the/etc/inittab displays the rows of a number (that is, a number between two colons;

Grep ': [0-9]:'/etc/inittab

5. display the lines starting with one or more blank characters in the/boot/GRUB/grub. conf file;

Grep '^ [[: Space:] \ {1, \}'/boot/GRUB/grub. conf

6. display the rows starting with a number in the/etc/inittab file and ending with the same number as the starting number;

Grep '^ \ ([0-9] \). * \ 1 $'/etc/inittab

Exercise:

1. Find one or two digits in a file;

Grep '[0-9] \ {1, 2 \}'/proc/cpuinfo

Grep -- color '\ <[0-9] \ {1, 2 \} \>'/proc/cpuinfo

2. Locate the integer between 1-In the ifconfig command result;

3. query the account information of the user whose name is student (the row must appear first) on the current system. The file is/etc/passwd.

Grep '^ student \>'/etc/passwd | cut-D:-F3

ID-u student

Student1

Student2

Exercise: analyze the features of the first two rows in the following text in the/etc/inittab file (the numbers in each row must be the same). Write a pattern similar to the two rows:

L1: 1: Wait:/etc/rc. d/RC 1

L3: 3: Wait:/etc/rc. d/RC 3

Grep '^ L \ ([0-9] \): \ 1. * \ 1 $'/etc/inittab

4. Bash basics and configurations, standard I/O, pipelines, and shell programming basics;