BASH LOOPS

Loop is to repeat some code continuously and exit based on the some expression evaluation.

FOR LOOP

basic for loop struct:

for statement

do

       commands block

done

there are quite a few common examples

• for variable in 1 2 3 4 5
• for variable in {1..5}
• for i in $(seq 1 2 100)
• for day in Monday Tuesday Wednesday Thursday Friday Saturday Sunday
• for argument in "$*"
• for(( integer = 1; integer <= 5; integer++ ))
• for(( a=1, b=5; a <= 5; a++, b-- ))

WHILE LOOP

while expression

do

       commands block

done

the statement will be evaluated if true then will do the block, and re-evaluate the expression. The loop will exit untile the expression is false.
unitl loop is quite similar but until will always execute the loop at least once then evaluate the expression

break exit the loop

continue ignore the left loop block and continue an new loop

SELECT LOOP

select is very similar to the case statement in bash, it provides an interactive user interface.

Here is the sample code for user to select from a specified list

echo "What is your favorite color? "

select color in "red" "blue" "green" "white" "black"

do

    if [ $color ] ; then

              echo "You have selected $color"

              break

       else

              echo "Invalid selection"

       fi

done

it will ask the user to key in a

such as

what is your favorite color?

1)      red

2)      blue

3)      green

4)      white

5)      black

#? Red

Invalid selection

#? 0

Invalid selection

#? 1

You have selected red