Shell Script Tutorial

Logic - FOR

Example 1 :

for i in 1 2 3 4 5; do echo "Welcome $i times" done

Resuit:
Welcome 1 times
Welcome 2 times
Welcome 3 times
Welcome 4 times
Welcome 5 times

Example 2 :

for i in `cat /tmp/shadow`; do
        id=`echo $i | cut -d ':' -f1,1`
        echo ""
        echo "[$id]     password is changed"
        echo -e "123456\n123456\n" | passwd $id
done

This scripts is used to changed password for mass linux account.

Example 3 :

for (( i = 0; i <= 5; i++ )); do
	echo "Welcome $i times"
done

Resuit:
Welcome 1 times
Welcome 2 times
Welcome 3 times
Welcome 4 times
Welcome 5 times

Example 4:

for (( i = 1; i <= 5; i++ )); do      ### Outer for loop ###

    for (( j = 1 ; j <= 5; j++ )); do    ### Inner for loop ###
          echo -n "$i "
    done

   echo "" #### print the new line for break ###

done

This is nesting of FOR loop, Resuit:
1 1 1 1 1
2 2 2 2 2
3 3 3 3 3
4 4 4 4 4
5 5 5 5 5

Example 5:

for (( i = 1; i <= 9; i++ )); do   ### Outer for loop ###
   for (( j = 1 ; j <= 9; j++ )); do  ### Inner for loop ###
        tot=`expr $i + $j`
        tmp=`expr $tot % 2`
        if [ $tmp -eq 0 ]; then
            echo -e -n "\033[47m "
        else
            echo -e -n "\033[40m "
        fi
   done
   echo -e -n "\033[40m" #### set back background colour to black
   echo "" #### print the new line ###
done

This chess-board will be printed with this nesting of FOR loop.

Example 6:


f1="/tmp/word1.txt"
f2="/tmp/word2.txt"


for i in `cat $f1`; do

    for j in `cat $f2`; do
        if [ $i = $j ]; then
            echo $i 
        fi
    done

done

This script is designed to get the same word/line compare between with 2 files.

Example 7:


IFS=$'\n'
for i in `cat /tmp/log`; do
        echo $i
done

For loop to count each line without white space problem