Shulou(Shulou.com)06/03 Report--

Summary of Shell language

Shell variable

1. User customization: identifier

Assign values from right to left

Reference variable $

Clear the variable $unset Z

For example, $count= 1

$echo$HOME

two。 Command line argument variable

$0 contains the script file name as on the command line of the typed line

$1 the first parameter

$2

$3

3. Location variable

$@ contains the command line argument "$1 $2 $3 $4 $5 $6 $7 $8x9"

$* contains the command line argument "$1 $2 $3 $4 $5 $6 $7 $8x9"

$# contains the number of command line parameters

$? Contains the exit status of the previous command

$contains the number of the process being executed

4. Environment variable: env

Search path for $PATH shell

User directories listed in the $HOME / etc/passwd file

$IFS defaults to spaces tab and newline characters

Vt100,ansi,vt200.xterm is commonly used in $TERM terminal type.

two

Shell statement

1. Declarative statement # x

two。 Functional statement read (read one line from standard input)

Expr (arithmetic operation command)

Test (file attribute string integer)

1.test $name-eq $1

Echo $?

2if test-f $filename

Then

……

Fi

3if [- f $filename]

Then

……

Fi

4. Integer test

A-eq b tests whether an is equal to b

A-ne b tests whether an and b are not equal

A-gt b tests whether an is greater than b

A-ge b tests whether an is greater than or equal to b

A-lt b tests whether an is less than b

A-le b tests whether an is less than or equal to b\

5. File testing

-d name tests whether name is a directory

-f name tests whether name is a normal file

-L name tests whether name is a symbolic link

-r name tests whether the name file exists and is readable

-w name tests whether the name file exists and is writable

-x name tests whether the name file exists and is executable

-s name tests whether the name file exists and its length is not 0

F1-nt f2 test whether the file F1 is newer than the file f2

F1-ot f2 test whether the file F1 is older than the file f2

III. Structural statement

1. If mode

Then

Fi

2.if expression

Then

Command list

Else

Command list

Fi

Remember that-f detects whether it is a file-d detects whether it is a directory

4. Divisional sentence

Case string variable in (case can only detect string variables)

Constant string) / / if the variable name is equal to the constant string, execute command 1

Command Table 1

Constant string)

Command Table 2

Constant string)

Command Table 3

Constant string)

Command Table 4

*) / / * indicates other modes

Command 5

Esac

5 loop statement

A) for variable name in variable list

Do

Command list

Done

Variables take each word in the vocabulary in turn, and each time the word is taken, the command in the loop body is executed. The number of cycles is determined by the number of words in the vocabulary. The commands in the command table can be one or multiple lines separated by semicolons or newline characters. If the word list is all positional parameters on the command line, you can omit the in word list section in the for statement. It will not end until the variable name takes all the variables in the variable list to the loop body.

6while expression

Do

Command table / / expression is true to execute command table

Done

The while statement first tests the value of the subsequent command or expression, if true, executes the command in the body of the loop, then tests the value of the command or expression, and executes the body of the loop until the loop exits when the command or expression is false.

The exit state of the while statement is the exit status of the last command executed in the command table.

7.until expression

Do

The command table / / expression is false until the expression is true to exit the loop

Done

The function of the until loop is similar to that of the while loop, except that the command table in the loop body is executed only when the value of the tested command or expression is false, otherwise the loop is exited. This is the opposite of the while command.

8break and continue

Mixed with loop statements

Break n jumps out of the n layer.

The continue statement immediately goes to the next loop of the nearest loop statement.

Continue n goes to the next loop of the nearest n-tier loop statement.

Shell function

Shell function

1. Function definition mode

Function_name ()

{

Command list / / play space

}

Function function_name () / / this is not commonly used

{

Command list / / play space

}

two。 Parameter transfer of function

Function_name 12$ value..

12: function body reference 12, represented by $1

Value: value is referenced in the function body, represented by $2

3. Function return value call

Represents the return status of the function: $?

1) A function with return $? A value that represents return

2) the function without return, $? The return state of the last instruction in the function

4. Function output content reference

Refer to the function output by anti-apostrophe, usually a string

Count= `function _ name $value`

5. Return value of function

Fun $value

Echo $?

The scope of the Shell variable

1. Local variables act on the body of the function

Keyword local

two。 Global variables act anywhere within the script

The contents of the variable after initialization are empty otherwise

Count= 5

3. Independent of the script file

Keyword export

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