Bash basics, gitbash

Bash basics, gitbash

 

1 concept

Bash (sh, pdsh extension): GNU Bourne-Again Shell

 

Sh: Bourne Shell, excellent programming and inconvenient user interaction.

Csh: C Shell. The programming interface is not as good as sh. the user interface is friendly and similar to the C language syntax. --> Tcsh

Ksh: Korn Shell, which integrates the advantages of sh and csh and is fully compatible with sh. --> Pdsh (Public Domain Korn Shell)

Zsh

 

2 syntax 2.1 variables, Data Type

Variable definition: it does not contain reserved words (such as "-, *"), and does not contain spaces.

Variable reference: assign a value. $ is not required before a for loop. In other cases, the referenced variable must contain "$" (for example, print, or computation ).

Data Type: shell variables do not have data types.

Shell statement: = left and right cannot have spaces; shell statements do not end.

2.1.1 integer calculation (+-*/%): let, expr

1) let: Double quotation marks

For example, let "x = $ x + 1"

2) expr: ', space. escape characters must be used before special characters \

For example, x = 'expr $ x + 4', x = 'expr $ x \ * 4'

[PS] does not support floating-point calculation. It does not have a floating-point data type.

[Example: arithmetic operation, character concatenation, and no data type of shell]

#! /Bin/bash

X = 2007

Let "x = $ x + 1"

Echo $ x

 

X = 'expr $ x + 4'

Echo $ x

Echo $ (expr $ x/2)

X = 'olmpic '$ x

Echo x = $ x

 

Y = 12

Y = 'expr $ y \ * 2'

Echo $ y

 

2.1.2 assignment

X = 200

Let "x = $ x + 1"

X = 'hello' $ x

Y = $ (expr $ x/2)

Y = 'expr $ y \ * 2'

 

Result = $ ($ result + $ num ))

Num = $ (num + 1 ))

 

2.1.3 comparison

1)-eq,-ne,-gt and-ge,-lt and-le,-z (empty),-n (non-empty)

2) = ,! =,> (None> =), <(none <=)

[PS]

When comparing strings, try not to use-z! -N instead.

Can use 1) Try not to use 2 ).

 

2.1.4 bitwise operation

&, |

Bitwise operation :]

Ckm @ bidc :~ /ZzhTest> echo $ (expr 1 \ & 0)

0

Ckm @ bidc :~ /ZzhTest> echo $ (expr 1 \ | 0)

1

#! /Bibn/bash

If [$ str! -N]; then

Echo null !!

Fi

 

2.2 process control 2.2.1 if condition control

If [expression]; then statements

Fi

 

If [expression]; then statements

Else statements

Fi

 

If [expression]; then statements

Else if [expression] then statements

Else statements

Fi

 

If [expression]; then statements

Elif [expression]; then statements

Else statements

Fi

[PS]

If the then line breaks, the then does not need to be added before it ;.

There are spaces before and after [and.

 

2.2.2 case Branch Structure

Case "$ var" in

Cindition1) statements ;;

Cindition2) statements ;;

...

*) Statements ;;

Esac

 

 

 

2.2.3 for Loop

For var in [list]; do

Statements

Done

[PS]

The var variable reference does not use $.

<List> elements are separated by spaces.

 

2.2.4 while LOOP

While [condition]

Do

Statements

Done

 

 

2.2.5 until Loop

Until [condition]

Do

Statements

Done

 

 

2.2.6 break/continue

 

3. Execute the bash script example "hello world": hello

#! /Bin/bash

# Use of Variables

Str = 'Hello world'

Echo $ str

Echo str

 

-- Execution File

Bash hello

Sh hello

Chmod u + x hello

Hello

 

Common Linux commands]

Vi zzhdir

#! /Bin/bash

Ls-

-- Execute

Sh zzhdir

 

[Local variables: scope of local variables (in the function body )]

#! /Bin/bash

Function test {

Local var = world

Echo $ var

}

 

Var = hello

 

Echo $ var

Test

Echo $ var

[PS] local variable: When a value is assigned for the first time, the variable is prefixed with local.

 

[If condition: Compare operation, if condition control structure]

#! /Bin/bash

A = 10

If [$ a-gt 0]

Then echo 1

Else echo 2

Fi

 

[If condition: script with parameters]

#! /Bin/bash

If [$1 = 10]; then echo right!

Else echo wrong!

Fi

-- Execute

Sh test 123

[PS] $1 is used to match the 1st parameters of the command line. (Reserved Words in bash)

 

[Case Branch]

Var = 12

Case "$ var" in

[A-z]) echo 'lowercase letter! ';;

[0-9]) echo 'number ';;

*) Echo other character !;;

Esac

 

[For Loop: No in [list]

For var; do

Echo OK

Done

-- Execute

Sh test

Sh test 1 "hello world"

 

[For Loop: Scope of I] inside the loop body (between do and done)

For I in $ (seq 5)

Do

Echo $ I

Done

 

Echo $ I

-- Execute

Sh test

 

[For Loop: seq]

For I in 'seq 1 5'; do

Echo TEST!

Done

 

[For Loop: Scope of I] block after Definition

For (I = 1; I <= 5; I ++); do

Echo $ I

Done

Echo $ I

-- Execute

Sh test

 

For Loop: command line parameters ].

For param

Do

Echo $ param

Done

-- Execute the script

Sh test 123 456 789

[PS] If list is not specified, all command line parameters are printed. If no command line parameter is specified, nothing is printed.

 

[While loop]

Num = 1

Result = 0

While [$ num-le 3]

Do

Result = $ ($ result + $ num ))

Num = $ (num + 1 ))

Done

 

Echo $ result

 

[Until loop]

Num = 1

Result = 0

Until [$ num-ge 3]

Do

Result = $ ($ result + $ num ))

Num = $ (num + 1 ))

Done

 

Echo $ result

 

[Break/continue]

For I in 'seq 1 5'; do

If [$ I = 3];

Continue

Else echo $ I

Fi

Done

 

 

4 Vi Editor

Naming mode: Esc key, ":" colon, "wq" Save and exit, "q !" Force exit

Insert mode: aAiIuU

Delete a word: dw

Delete the entire row: dd

String SEARCH: slash (/)

 

5. Related Expansion

Reserved Words

Regular Expression

Function

Input, output:>, >>,> 2,> 1,> &

For Loop

Function of a variable: integer, String, count, and file attribute

 

 

Cube

 

[Bash] $ what does it mean?

Is a prompt, bash is a type in shell scripts. In linux, $ code is a common user and # represents the root user.
It's all about linux. Learn more.

Concepts of Linux, Bash, and Shell

1. Yes
2. The difference is big. Writing bash shell doesn't mean you can write c shell, but I think you can write a shell script.
In addition, you can get started quickly. At least it should be difficult to understand. You can learn bash shell first because it is used more often.
It is also highly portable. bash is a type of shell.
3. As a shell, only bash shell is installed to run the bash shell script. It is not for a specific system or release version.
Shell can be installed at will. Which shell do you like to use? You can install a shell independently even if it is not in the initial installation system.
4. I recommend two books for you.
Bash shell advanced script Guide
Practical LINUX + SHELL programming and Server Management

Shell programming can be said to directly reflect your proficiency in linux commands, and under what circumstances which commands are better suited
How can you simplify the script running process and optimize the script to make it more efficient.
You will inevitably be exposed to stream editors like sed and awk in your learning process. Then you have to learn sed and awk.
Gradually it is estimated that you should choose a more powerful programming language, instead of simply writing shell scripts, such as perl. python and php.
C, or what language... is basically this process.