Shell Script Programming Notes

1. The first line must specify the shell used: #!/bin/bash/2, Print command: Echo

-N: Suppress line breaks

3. Use command line parameters:

$#: The number of command-line arguments passed in the script

$*: All command-line parameter values, with a space between each parameter value (as a word processing)

[Email protected]: All command line parameter values (processed as multiple words)

$: Command the Province (shell file name)

$: First command-line argument

$: Second command-line argument

Gets the last parameter of the user input ${!#} cannot be used with ${$#}

4. Mathematical calculation:

Expr does mathematical calculations

To assign the result of the calculation to other variables, you need to add an inverse quote.

5. If statement:

if[condition] #condition前后都要有空格

Then

Commands

Else

Commands

Fi

If nesting:

If Command1

Then

Command2

Elif Command3

Then

Command4

Fi

6. Condition Comparison:

-eq Same

-ne different

-GT Greater than

-lt less than

-ge greater than or equal to

-le less than or equal to

-Z is empty

-N is not empty

7. String comparison:

STR1 = str2 Check if str1 is the same as str2

!=

<

>

-N str1 Check if str1 length is greater than 0

-Z str1 Check if str1 length is 0

8, file comparison:

-d file checks if file exists and is a directory

-e file checks if file exists

-F File checks if file exists and is a file

-r file checks if file exists and is readable

-S file checks if file exists and is not empty

-W file checks if file exists and is writable

-X file checks if file exists and is executable

-O file checks if file exists and is owned by the current user

-G file checks if file exists and whether the default group is the current user group

File1-nt file2 Check if file1 is newer than file2

File1-ot file2 Check if file1 is older than file2

#两个条件同时满足

If [Condition1] && [Condition2]

Then

Command1

Fi

#两个条件其中一个满足

If [Condition1] | | [Condition2]

Then

Command1

Fi

#取反

if [! condition]

Then

Command1

Fi

Double parenthesis:

((Command1)) #允许像C一样的操作

Case statement:

Case variable in

PATTERN1)

Command1;;

PATTERN2)

Command2;;

*) # * Number indicates other values

default commands;;

Esac

9. For statement:

Method 1:

for Var in list

Do

Commands

Done

Method 2:

for ((i = 0;i < 10;i++))

Do

Commands

Done

10. Read the data from the file:

file= "FileName"

For data in ' cat $file '

Do

echo "Data is $data"

Done

11. IFS: Changing the internal field delimiter

General usage:

Ifs_old= $IFS

ifs=$ ' \ n ':;

Code

ifs= $IFS _old

12. Get the files and sub-files in the current directory:

#for file in ' pwd '/* #通配, all files in the current directory

For file in ' find '

Do

If [-D "$file"]

Then

echo "$file is a directory"

Elif [-F "$file"]

Then

echo "$file is a file"

Fi

Done > Output.txt #重定义循环输出

13, getopts command: getopts optstring variable

Parameters:

Optstring: Option string

Variable: Parameters

If the option letter requires a colon after the parameter value

If you want to suppress output error messages, start the option string with a colon

Instance:

While Getopts ab:opt

Do

Case ' $opt ' in

A) echo "found–a option";;

b) echo "found–b option with value $OPTARG";;

Esac

Done

Options	Describe	Options	Describe
-A	Show All Objects	-N	Use non-interactive (batch) mode
-C	Build Count	-O	Specify an output file to redirect the output
-D	Specify directory	-Q	Execute in quiet mode
-E	Expand objects	-R	Recursively process directories and files
-F	Specify a file to read data from	-S	Execute in silent mode
-H	Show Help for a command	-V	Generate verbose output
-I.	Ignore case	-X	Exclude and Reject
-L	Output of the number of raw growth	-Y	Set the answer to all questions Yes

Table 13.1 Common Linux command-line options

14. Read user input:

Basic reading Read

Read if no variable is specified, the default is stored in the environment variable $reply

-P: A prompt can be specified directly in the Read command

-T: Specify a wait input time, usage-t

eg

If read–t 5–p "Plase input your Name:" Name #会输入到错误流 ...

Then

Echo $name

Else

Echo–e "\nyou is too slow"

Fi

-N: Specifies the number of characters entered and automatically ends the input when the number of characters specified in n is reached, followed by the number of characters to be entered directly after the use of-n

-S: User input is not displayed on the window, such as when entering a password

15. Redirect:

To redirect Stdeer and StdOut separately:

Eg:ls–al test1 test2 2> error.txt 1> right.txt

REDIRECT Stdeer and stdout to the same file: Redirect with &>

Temporary redirection:

Eg:echo "This was an error" >&2 #重定向到错误流

./bash.sh 2> Tmp.txt #重定向错误流到tmp

Permanent redirection: (Cannot switch back)

exec 1> File

EXEC 2> Errfile

Redefine input: (cannot switch back)

EXEC 0< Inputfile

REDIRECT File descriptor: (can switch back)

Save 1 (STDOUT) with the file descriptor 3

EXEC 3>&1

EXEC 1>file

echo "someing write to File"

EXEC 1>&3

Save 0 (STDIN) with the file descriptor 4

EXEC 4<&0

EXEC 0<file

While Read line

Do

Echo $line

Done

EXEC 0<&4

To close the file descriptor:

EXEC 3>&-

List Open file descriptors:

/usr/bin/lsof

Suppress command output:

Commond >/dev/null #输出到空文件

/dev/null >file #清空file里面的所有内容

To create a temporary file:

Mktemp

-T: Create a temporary file under/tmp

-D: Create a temp directory

file= ' Mktemp–t temp. XXXXXX '

Message logging:

Tee: Prints the message in the file specified by stdout and tee

Tee filename

-a writes the filename in append mode

16. Script Control

Stop signal: CTRL + C

Stop signal: CTRL + Z

Signal capture: Trap commands signals

Trap "echo Hello World" SIGINT SIGTERM

Some commands are executed before the script exits:

Trap "Echo Exit" exit

Removal Capture: trap-exit

Run the script without using the console: Nohup./xx.sh &

View Jobs: Jobs

Parameters	Describe
-L	List PID and job numbers for a process
-N	Only jobs that have changed state since the last shell notification were listed
-P	List only the PID of the job
-R	List only jobs that are running
-S	List only jobs that are stopped

Table 16.1 Job Command parameters

Restart stopped jobs: BG Job number FG Job number (running in the background)

17. Array variables and functions

The delivery of the array:

myarray= (0 1 2 3 4 5 6)

Farray ${myarray[*]}

The function receives an array:

function Farray

{

Local NewArray

newarray= (' echo ' [email protected] ')

echo "New array is: ${newarray[*]}"

echo "The third number is: ${newarray[2]}"

}

18. Create a library

. Pathname Loading Library

or source pathname #pathname为库的名称含路径如:./mylib

19. Add Color

eg:^[[33m

^[is a combination of CTRL + V followed by a [need to add yourself

20. SED programming

Replacement: S/pattern/replacdment/flags

Flags

-Number: Indicates the mode of new text substitution

-G: Indicates that all characters of existing text are replaced with new text

-P: The line in the printed text that contains the replacement string is often used with the-N (no sed editor output)

-W File: Writes the result of the substitution to a file

eg:sed ' S/TEST/TRIAL/2 ' data #替换每行的第二个test

Use Address:

eg:sed ' 2,3s/dog/cat/' file #只替换2, 3 rows of dog

Sed ' 2, $s/dog/cat/' file #从第2行开始替换知道末尾

Delete Row: D (delete from output only, original file unchanged)

Eg:sed ' 2d ' data #删除第2行

Inserting and attaching text:

Sed ' [address]command\

New Line '

Command

I: Add a new row before the specified line

A: Add a new line after the specified line # $a \ Add at the end of the file

Eg:echo "Testing" | Sed ' i\

>this is a test '

Change row: C

Eg:sed ' 3c\

>this is a changed line ' data

Replace command sed ' y/inchars/outchars/'

eg:sed ' y/123/789/' data #1->7 2->8 3->9

Write file: [address]w filename

Read file: [address]r filename

21. Regular Expressions

Special characters in regular expressions:. *[]^${}\+| () #作为文本字符需要转义 \

Locator:

^[address] #address只能出现在文本开头的位置

[Address]$ #address只能出现在文本结尾的位置

To find a row of data that contains only a specific text pattern:

Sed–n '/^this is a test$/p ' data

Remove empty line: sed '/^$/d ' data

Dot character:. #通配一个字符 eg:sed–n '/.at/p ' data # XAT

Character class: Echo "Yes" | Sed–n '/[yy]es/p ' #yes或Yes匹配

echo "Yes" | Sed–n '/[yy][ee][ss]/p ' #yes/yes/yes ...

Negative character class: Sed–n '/[^ch]at/p ' data #xat in addition to cat and hat

Use range: [0-9] #匹配0-9 value

Special characters

*: Can not appear or appear multiple times

?: Can not appear or appear once

+: appears at least once

{}:--->

M: happens to happen m times

M,n: Appears at least m times up to N times

|: Or, enclosed in ()

(| |-|) : Either there is either a space or a-number

( |-|) : Space OR-no

Note: Gawk does not recognize the regular expression and must be prefixed with the--re-interval command

Shell Script Programming Notes