Shell scripting: program controls part 1

Welcome to art of scripting!!

Here I am posting a list of experiments on bash shell if condition command.

• 1. if-fi condition

  2. if-else-fi condition

  3. if-elif-else-fi ladder

Lets test with numeric variable values and also test file exist or else using the true or false command in the if condition.

#!/bin/bash################################################################################ FileName              :       simpleif.sh## Author                :       Pavan## Updated date          :       28/01/2016## Description           :       This script will be use to illustrate the if-fi###############################################################################if cat simpleif.sh; then  echo 'File display true because it exists'; fi# if will excute a command when no braces usedif [ -f simpleif.sh ]; then         echo "simpleif.sh file exists..."fi# boolean values are defined true, false remember case sensitiveif true; then         echo "True command"fiif ! false; then         echo "Not false that is true!!"fi

Execution of the above script will gives output as follows:

if-else-if condition in shell scripting

#!/bin/bashread -p "Please enter two numbers: " a b  echo "Given numbers: $a $b"if [[ $a > $b ]]; then   echo "a is greater than b"else   echo "b is greater than a"fi

Execution of the above script...

if-elif-else-if Ladder - Menu program in Shell script

#!/bin/bashecho "Choose your option"echo -e "\t1. Memory usage \n \        2. Disk usage \n \        3. CPU Utilization \n \        0. Quit \n"read ch if [[ ch -eq 1 ]]; then  echo -e 'The Memory usage...\n'; free -m elif [[ ch -eq 2 ]]; then  echo -e 'The Disk utilization lll\n'; df -h .elif [[ ch -eq 3 ]]; then  echo -e 'The CPU utlization ...\n'; uptime else         exitfi

Execution of the menu program will be as shown:

Logical operators in Shell script

#!/bin/bash# Description   : This script will illustrates the logical operator in shell script#c=1if [[ 10 < 30 && $c < 5 ]]; then         echo "a is true"fiif (( $c && 1 )); then  echo -e "all true..."else  echo "something wrong"fiif [[ $c -lt 10 ]] || [[ 100 -gt $c ]]; then         echo "Either one of them is true..."else         echo "Both are false"fi

Execution of logical.sh script as follows: