Bash For Loop Examples (For and Read-While Loops in Bash)

Today, We want to share with you bash for loop.In this post we will show you For and Read-While Loops in Bash, hear for for loop in unix shell script to read a file we will give you demo and example for implement.In this post, we will learn about bash tutorial with an example.

How to write a loop in Bash?

Bash supports the following looping constructs.

Loops in Bash

  • while
  • for
  • until

Basic syntax

for product in dog cat 'mobile elec' elephant ostrich
do
  echo "I want a $product for a iphone"
done

for data in $collection_of_things
do
  some_program $data
  another_program $data >> products.txt
  # as many commands as we want
done

for var_name in $(seq 1 100); do
  echo "Counting $var_name..."
done

for url in $(cat all_website_ulrs.txt); do
  curl "$url" >> full_sourcecode_online.html
done

while read url
do
  curl "$url" >> full_sourcecode_online.html
done < all_website_ulrs.txt

Basic ‘For Loop’ Example

Bash Script

#!/bin/bash  
#This is the basic example of 'for loop'.  
  
understand="Start understanding from Pakainfo."  
  
for understand in $understand  
do  
echo $understand  
done  
  
echo "Thank You."  

For Loop to Read a Range

Bash Script

#!/bin/bash  
#This is the basic example to print a series of numbers from 1 to 10.  
  
for num in {1..10}  
do  
echo $num  
done  
  
echo "Series of numbers from 1 to 10."  

For Loop to Read a Range with Increment/Decrement

For Increment

#!/bin/bash  
  
#For Loop to Read a Range with Increment  
  
for num in {1..10..1}  
do  
echo $num  
done  

For Decreament

Bash Script

#!/bin/bash  
  
#For Loop to Read a Range with Decrement  
  
for num in {10..0..1}  
do  
echo $num  
done  

For Loop to Read Array Variables

Bash Script

#!/bin/bash  
  
#Array Declaration  
arr=( "Welcome""to""Pakainfo" )  
  
for cnt in "${arr[@]}"  
do  
echo $cnt  
done  

Read a file, line-by-line, reliably with read-while

[email protected]:~$ for line in $(cat list-of-dirs.txt)
> do
>    echo "$line"
> done

For Loop to Read white spaces in String as word separators

Bash Script

#!/bin/bash  
#For Loop to Read white spaces in String as word separators  
  
websitename="Let's start  
understanding from Pakainfo."  
  
for cnt in $websitename;  
do  
echo "$cnt"  
done  

For Loop to Read each line in String as a word

Bash Script

#!/bin/bash  
#For Loop to Read each line in String as a word  
  
websitename="Let's start  
understanding from   
Pakainfo."  
  
for cnt in "$websitename";  
do  
echo "$cnt"  
done  

For Loop to Read Three-expression

Bash Script

#!/bin/bash  
#For Loop to Read Three-expression  
  
for ((cnt=1; cnt<=10; cnt++))  
do  
echo "$cnt"  
done  

For Loop with a Break Statement

Bash Script

#!/bin/bash  
#Table of 2  
  
for table in {2..100..2}  
do  
echo $table  
if [ $table == 20 ]; then  
break  
fi  
done  

For Loop with a Continue Statement

Bash Script

#!/bin/bash  
#Numbers from 1 to 20, ignoring from 6 to 15 using continue statement"  
  
for ((cnt=1; cnt<=20; cnt++));  
do  
if [[ $cnt -gt 5 && $cnt -lt 16 ]];  
then  
continue  
fi  
echo $cnt  
done  

Infinite Bash For Loop

Bash Script

#!/bin/bash  
  
cnt=1;  
for (( ; ; ))  
do  
sleep 1s  
echo "Current Number: $((cnt++))"  
done  

Loops for, while and until

For sample
The for loop is a little bit different from other programming languages. Basically, it let’s you iterate over a series of ‘words’ within a string.

#!/bin/bash
for cnt in $( ls ); do
    echo product: $cnt
done

C-like for

#!/bin/bash
for cnt in `seq 1 10`;
do
        echo $cnt
done    

While sample

#!/bin/bash 
 COUNTER=0
 while [  $COUNTER -lt 10 ]; do
     echo The counter is $COUNTER
     let COUNTER=COUNTER+1 
 done

Until sample

   #!/bin/bash 
         COUNTER=20
         until [  $COUNTER -lt 10 ]; do
             echo COUNTER $COUNTER
             let COUNTER-=1
         done

Arrays in Bash

#!/bin/bash

products=( A B C D E F G )
echo "${products[0]}"
echo "${products[1]}"
echo "${products[2]}"
echo "${products[3]}"
echo "${products[4]}"
echo "${products[5]}"
echo "${products[6]}"

Looping over Arrays

#!/bin/bash

members=(rahika sejal Jake Scott Philis)
for m in "${members[@]}"
do
    echo "$m is a registered member"
done

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