Writing a For loop and a while loop case with the shell

(1) difference between single and double quotes in the shell

?? A= "Www.jfedu.net"

?? b= ' $A '

? Echo $B

Comments:?

Assign the www.jfedu.net to variable A, assign the contents of variable A to the variable B, print out the result of the variable B, and print the result as $ A

?????? Because the variable A is a weak reference, the result of the reference is just one character

A= "Www.jfedu.net"

b= "$A"

Echo $B

Comments:

? ? ? ? ? ?? Assign www.jfedu.net to variable A, assign the contents of variable A to the variable B, print out the result of the variable B, and print the result as www.jfedu.net

? ? ? ? ? ? Because variable A is a strong reference, the reference result of variable B is www.jfedu.net, not a character

(2) for loop syntax format

? ? For? Var? In (an expression)

? ? Do

???????????? Statement

? ? Done

(3) Print 1 to 100 with for loop

? ? For I??? ' SEQ 1 100 '

? ? Do

? ? ? ? Echo $i

? ? Done

Note: Single and double quotation marks only apply to variable references, calculations are not possible, single and double quotes are not used

??

Expand

1 to 100 other two ways to print with a for loop

? For? I?? in? $ (SEQ 1 100)

? Do

??? Echo $i

? Done

? For I? In? ' Echo? {1..100} '

? Do

??? Echo $i

? Done

Note: Do not forget to add a space after echo, do not add space, will error

(4) Read the file contents with a For loop and print to the screen

? For I? In? ' Cat List.txt '

? do

??? Echo $i

Done

(5) Batch to remote host with for loop execution command

? Command= "$*"

? For? I???? ' Seq 1 100 '

? Do

???? ssh-l? Root? 192.168.1. $i? "$command"

? Done

(6) Bulk transfer of files to a remote host with a For loop

? files= "$*"

? For? I?? in? ' SEQ 1 100 '

? do

? scp-r $files [email protected] $i:/tmp

Done

(7) Output 1 to 100 with a For loop and

? j=0

For I? In? ' SEQ 1 100 '

Do

?? j= ' expr $i + $j '

Done

Echo $j

(8) While loop format

? While? (expression)

? Do

? ? ? Statement

? done

(9) Use while loop to read the contents of the file list and print the results on the screen

? while read line

? do

? ? ? Echo $line

? done<list.txt

(10) using the while loop to output hello on the screen every second? Word

? While? Sleep 1

? Do

? ? ? echo "Hello word"

? Done

(11) Use while loop to print 1 to 100

? I=0

? while (i<=100)

? do

??? Echo $i

? ? ? i= ' expr $i +1 '

? done

The while loop prints 1 to 100 of the and

? J=0

? I=1

? while (i<=100)

? Do

????? j= ' expr $i + $j '

? ? ? ? ((i++))

? done

? echo $j????

?

Writing a For loop and a while loop case with the shell