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Conditional Statements: There are total 5 conditional statements which can be used in bash programming
if statement
if-else statement
if..elif..else..fi statement (Else If ladder)
if..then..else..if..then..fi..fi..(Nested if)
switch statement
Here are some useful examples of if-else in shell scripts to give you a better idea of how to use this tool.
| Command | Description |
| && | Logical AND |
| $0 | Argument 0 i.e. the command that’s used to run the script |
| $1 | First argument (change number to access further arguments) |
| -eq | Equality check |
| -ne | Inequality check |
| -lt | Less Than |
| -le | Less Than or Equal |
| -gt | Greater Than |
| -ge | Greater Than or Equal |
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| # ############################################ | |
| # Program - 1 - Format | |
| # ############################################ | |
| if [condition] | |
| then | |
| statement1 | |
| else | |
| statement2 | |
| fi | |
| # ############################################ | |
| # Program - 2 - Using if-else to check whether two numbers are equal | |
| # ############################################ | |
| #!/bin/bash | |
| m=1 | |
| n=2 | |
| if [ $n -eq $m ] | |
| then | |
| echo "Both variables are the same" | |
| else | |
| echo "Both variables are different" | |
| fi | |
| # ############################################ | |
| # Program - 3 - Using if-else to compare two values | |
| # ############################################ | |
| #!/bin/bash | |
| a=2 | |
| b=7 | |
| if [ $a -ge $b ] | |
| then | |
| echo "The variable 'a' is greater than the variable 'b'." | |
| else | |
| echo "The variable 'b' is greater than the variable 'a'." | |
| fi | |
| # ############################################ | |
| # Program - 4 - Using if-else to check whether a number is even | |
| # ############################################ | |
| #!/bin/bash | |
| n=10 | |
| if [ $((n%2))==0 ] | |
| then | |
| echo "The number is even." | |
| else | |
| echo "The number is odd." | |
| fi | |
| # ############################################ | |
| # Program - 5 - Using if-else as a simple password prompt | |
| # ############################################ | |
| #!/bin/bash | |
| echo "Enter password" | |
| read pass | |
| if [ $pass="password" ] | |
| then | |
| echo "The password is correct." | |
| else | |
| echo "The password is incorrect, try again." | |
| fi | |
| # ############################################ | |
| # Program - 6 - if-elif-if.sh | |
| # ############################################ | |
| #!/bin/bash | |
| #Purpose: Find biggest Number among 4 digits | |
| # START # | |
| echo -e "Please Enter a Value: \c" | |
| read -r a | |
| echo -e "Please Enter b Value: \c" | |
| read -r b | |
| echo -e "Please Enter c Value: \c" | |
| read -r c | |
| echo -e "Please Enter d Value: \c" | |
| read -r d | |
| if [ $a -gt $b -a $a -gt $c -a $a -gt $d ]; then | |
| echo "$a a is big" | |
| elif [ $b -gt $c -a $b -gt $d ]; then | |
| echo "$b b is big" | |
| elif [ $c -gt $d ]; then | |
| echo "$c c is big" | |
| else | |
| echo "$d d is big" | |
| fi | |
| # END # | |
| # ############################################ | |
| # Program - 7 - if-elif-if.sh | |
| # ############################################ | |
| #!/bin/bash | |
| #Purpose: If else statement example | |
| # START # | |
| echo -e "Enter any value: \c" | |
| read -r a | |
| echo -e "Enter any value: \c" | |
| read -r b | |
| if [ $a -gt $b ]; then | |
| echo "$a is greater than $b" | |
| else | |
| echo "$b is greater than $a" | |
| fi | |
| # END # | |
| # ############################################ | |
| # Program - 8 - if-elif-if.sh | |
| # ############################################ | |
| #!/bin/bash | |
| #Purpose: If statement example | |
| # START # | |
| echo -e "Please provide Value below ten: \c" | |
| read -r value | |
| if [ $value -le 10 ] | |
| then | |
| echo "You provided value is $value" | |
| touch /tmp/test{1..100}.txt | |
| echo "Script completed successfully" | |
| fi | |
| # ############################################ | |
| # Program - 9 - Nested If | |
| # ############################################ | |
| #!/bin/bash | |
| #Purpose: Validate and report Student subject marks | |
| echo -e "Please Enter Maths Marks: \c" | |
| read -r m | |
| echo -e "Please Enter Physics Marks: \c" | |
| read -r p | |
| echo -e "Please Enter Chemistry Marks: \c" | |
| read -r c | |
| if [ $m -ge 35 -a $p -ge 35 -a $c -ge 35 ]; then | |
| total=`expr $m + $p + $c` | |
| avg=`expr $total / 3` | |
| echo "Total Marks = $total" | |
| echo "Average Marks = $avg" | |
| if [ $avg -ge 75 ]; then | |
| echo "Congrats you got Distinction" | |
| elif [ $avg -ge 60 -a $avg -lt 75 ]; then | |
| echo "Congrats you got First Class" | |
| elif [ $avg -ge 50 -a $avg -lt 60 ]; then | |
| echo "You got second class" | |
| elif [ $avg -ge 35 -a $avg -lt 50 ]; then | |
| echo "You Got Third Class" | |
| fi | |
| else | |
| echo "Sorry You Failed" | |
| fi | |
| # END # |
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