shell for loop example

for_loop_example_1.sh

$ c=1
$ echo $c
1


$ for c in {1..9}; do echo -n $c; done
123456789
# {1..9} will expand to 1 2 3 4 5 6 7 8 9 .
# The for loop will loop through these words , 
# and echo will echo the words . -n is used 
# to suppress the printing of a new line .

$ echo $c 
9


$ for var in red blue green; do echo  $var; done
red
blue
green
# Loop through the three words , red blue and 
# green . Execute the command echo . The result 
# of executing the for loop is that red , blue
# and green are echoed out to the standard output
# each on a separate line .


$ for file in *; do echo $file; done
file1 
file2
# print the name of the file in the current
# working directory . * is substituted 
# by the shell with all the file 
# names in the current directory .


$ for file in `echo hey hi | wc`
> do 
>     echo $file; 
> done
1        # number of lines 
2        # number of words  
7        # number of characters
# Execute the echo command , 
# and redirect its output to 
# wc , wc will count the number 
# of lines words and characters ,
# its output will be 
#        1       2       7
# loop through the words , and 
# execute the echo command , and 
# finally the result of the looping 
# is displayed to the standard output .
# The preceding for loop command 
# could have been written as :
# for file in `echo hey hi | wc`; do echo $file; done
# but using the first notation is clearer .


# A for loop script named cls , which can 
# be used to clear the screen .


#!/bin/sh
# The script can be executed
# either using ./cls , or 
# ./cls 20 

counter=${1-25}
# Check if an argument is passed
# to the script , if so
# the counter variable will
# have its value , otherwise 
# the counter is initialized 
# to a value of 25 

for i in `seq 1 $counter`
# Use the seq command , to 
# generate words between 1
# and counter , and loop
# over these words , executing
# echo , which will just echo
# a new line .
do
    echo
done
# The result of executing the 
# script is clearing the screen .