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 $cnt
done
Read a file, line-by-line, reliably with read-while
user@host:~$ 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
I hope you get an idea about bash script example.
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