Shell Learning Notes (Org-mode production)

S Shell Learning Note v1.0table of Contents

• 1. What's shell
• 2. Hello World Program
  • 2.1. SRC
  • 2.2. Add run Privilege
  • 2.3. Run shell
• 3. variables in Shell
  • 3.1. System variables
  • 3.2. User Defined variables
    • 3.2.1. Define and use
    • 3.2.2. Local vs global variable
• 4. Control Structure
  • 4.1. Condition judgement
    • 4.1.1. Math operation judgement
    • 4.1.2. String Compara tion
    • 4.1.3. Logic judgement
    • 4.1.4. If-else
    • 4.1.5. For
    • 4.1.6. While
    • 4.1.7. Case
• 5. fucntion
• 6. Debug
  • 6.1. Echo
  • 6.2. Sh-v./shell or sh-x./shell

1 What is shell

Shell is the middle man of kernel and user.

1. To show shell installed in the system. Different shell may have differnet grammar

   Cat/etc/shells

2. Show current Shell used.

   Echo $SHELL

2 Hello World Program2.1Src

# !/bin/ SH Echo "Hello Shell"

2.2Add run Privilege

$ sudo chmod +x./helloshell.sh

2.3Run shell

./helloshell.sh

3 variables in Shell

Variables in shell is System variables and user defined variables.

3.1System variables

Use

$ set

To show the system variables.

3.2User Defined variables3.2.1Define and use

The variables in shell has no data type. Shell would automatically transfer the type. e.g.

msg="Hello World"

Attention:there is no blank spaces before and after ' = '

3.2.2Local vs global variable

Global shell variable stored in ~/.BASHRC, otherwise, they is all local shell variables.

4 Control Structure4.1Condition judgement

Use test or [] to judge a condition in shell.

4.1.1Math Operation judgement

seq	Example	explain
1	A-eq b	A = = B
2	A-ne b	A! = B
3	A-lt b	A < b
4	A-le b	A <= b
5	A-GT b	A > B
6	A-ge b	A >= b

4.1.2String comparation

seq	Example	explain
1	STR1 = str2	STR1 = = str2
2	Str1! = str2	Str1! = str2
3	Str1	STR1 NOT NULL or not defined.

4.1.3Logic judgement

seq	Example	explain
1	!	Not
2	Exp1-a EXP2	EXP1 && EXP2
3	Exp1-o EXP2	EXP1 or EXP2

4.1.4If-else

# !/bin/ SH if [$#    Then Echo "$0:you must give one integer"    exit 1fiif [$1then    echo' is positive "else    echo" is negative "fi

4.1.5For

# !/bin/ SH For i  in 1 2 3 4 5  does    echo"Welcome $i" Done

4.1.6While

#!/bin/SH# test While Loopif[ $#-ne 1]; Then    Echo "Usage: $ integer"    Exit1fiN=$1I=0 while[ $I-le 10] Do    Echo "$n * $i = ' expr $i \* $n '"    I=' expr $i + 1 ' Done

4.1.7Case

#!/bin/SH# test Case Statementif[ $#-ne 1]; Then    Echo "Usage: $ [a|b|c]"    Exit1fi Case$1inch    "a")Echo "a Select";;"B")Echo "B Select";;"C")Echo "C Select";; * )Echo "No Action";;Esac

5 fucntion

# !/bin/ SH Demo () {    echo"All function args: $*"    Echo"The first arg: $"    Echo  "The second arg: $"    Echo"The third arg: $"}Call the functiondemo-f foo barexit 0

6 Debug6.1Echo

Use the Echo to info.

6.2Sh-v./shell or Sh-x./shell

$ sh-v./shell Print the content shell get

$ sh-x./shell show the command then print it.

created:2015-07-23 Thu 22:20

Emacs 24.4.1 (ORG mode 8.3beta)

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Shell Learning Notes (Org-mode production)