Shell--if, Case Grammar detailed

1. Conditional Select if statement

Select Execute:

Single Branch

If judgment condition: Then

Branch code with true condition

Fi

Dual Branch

if judgment condition; Then

Branch code with true condition

Else

The condition is a false branch code

Fi

Multi-Branch

if CONDITION1; Then

If-true

Elif CONDITION2; Then

If-ture

Elif CONDITION3; Then

If-ture

...

Else

All-false

Fi

Judge by condition, when the first encounter is a "true" condition, execute its branch, and then end the entire if statement

If instance

Execute commands According to the exit status of the command

If ping-c1-w2 station1 &>/dev/null; Then

Echo ' Station1 is up '

elif grep "Station1" ~/maintenance.txt &>/dev/null

Then

Echo ' Station1 is undergoing maintenance '

Else

Echo ' Station1 is unexpectedly down! '

Exit 1

2. Conditional Judgment: Case statement

Case variable reference in

PAT1)

Branch 1

;;

PAT2)

Branch 2

;;

...

*)

Default Branch

;;

Esac

3. Practice:

1, write a script/root/bin/createuser.sh, to achieve the following functions:

Using a user name as a parameter, if the user who specified the parameter exists, the

otherwise added; Displays information such as the ID number of the user being added

Read "Input your username:" Input_user

ID $input _user

If [$?-eq 0]; then

echo "User exist"

Else

Useradd $input _user

Chk_id= ' getent passwd $input _user | Cut-d:-F 3 '

Echo $chk _id

Fi

? 2, write a script/root/bin/yesorno.sh, prompting the user to enter Yes or

No, and determine whether the user has entered Yes or no, or other information

#!/bin/bash

#

Read-p "Please input yes or no:" Input_info

[-Z "$input _info"] && (echo "error"; exit) | | Uperr_input_info= ' echo ' $input _info | tr [A-z] [a-z] '

Case $uperr _input_info in

y| yes|no| N

echo "Right"

;;

*)

echo "Other Info"

;;

Esac

3, write a script/root/bin/filetype.sh, determine the user input file path

File type (normal, directory, link, other file type)

#!/bin/bash

#

Read-p "Please input the path:" Path_file

If [-z] $path _file "];then

echo "You need to input info"; exit

Else

Type_file= ' Ls-ld $path _file | Cut-c1 '

echo "The type of the file is: $type _file"

Fi

4, write a script/root/bin/checkint.sh, determine the user input parameters

is a positive integer

#!/bin/bash

#

Read "Please input int:" Int_put

if [["$int _put" =~ ' ^[1-9]+$ ']]; then

echo "It is a int"

elif ["$int _put"-le 0]; then

Ehco "It is fu int or zero"

elif ["$int _put"-eq 0];then

echo "It is zero"

Else

echo "It is not a int"

Fi

#也可以使用 expr A + 0 to determine the type of a

Shell--if, Case Grammar detailed