diff --git a/sh/tests/calculator_test.sh b/sh/tests/calculator_test.sh
new file mode 100755
index 000000000..ea946ca78
--- /dev/null
+++ b/sh/tests/calculator_test.sh
@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+
+# set -euo pipefail
+IFS='
+'
+
+script_dirS=$(cd -P "$(dirname "$BASH_SOURCE")" &>/dev/null && pwd)
+
+challenge() {
+    submitted="./calculator.sh $@
+    "
+    expected="./calculator.sh $@
+    "
+    submitted+=$(2>&1 bash "$script_dirS"/student/calculator.sh "$@")
+    submitted+="
+    exit status: $?"
+    expected+=$(2>&1 bash "$script_dirS"/solutions/calculator.sh "$@")
+    expected+="
+    exit status: $?"
+
+    diff -U 1 <(echo "$submitted") <(echo "$expected")
+    if [ $? != 0 ]
+    then
+        exit 1
+    fi
+}
+
+# Check if student uses case statement
+if [[ $(cat "$script_dirS"/student/calculator.sh | grep case | wc -l) -eq 0 ]]
+    then
+    echo "Error: the use of case statement is mandatory"
+    exit 1
+fi
+
+# Valid inputs
+challenge "15" "+" "10"
+challenge "15" "-" "10"
+challenge "15" "/" "10"
+challenge "15" "*" "10"
+
+challenge "3491" "+" "-67"
+challenge "3491" "-" "-67"
+challenge "3491" "/" "-67"
+challenge "3491" "*" "-67"
+
+challenge "-3491" "+" "-67"
+challenge "-3491" "-" "-67"
+challenge "-3491" "/" "-67"
+challenge "-3491" "*" "-67"
+
+# Invalid inputs
+
+challenge
+challenge "-3491" "*" "-67" "10" "12"
+
+challenge "20" "/" "0"
+challenge "20" "@" "10"
+challenge "10" "*" "67invalid"
+
+# Test operators functions
+
+source $script_dirS"/student/calculator.sh" 10 + 10 >/dev/null 2>&1
+
+if [ $(do_add 11 14) != 25 ]
+then
+    echo "error in function do_add"
+    exit 1
+fi
+
+if [ $(do_sub 11 14) != -3 ]
+then
+    echo "error in function do_sub"
+    exit 1
+fi
+
+if [ $(do_mult 3 5) != 15 ]
+then
+    echo "error in function do_mult"
+    exit 1
+fi
+
+if [ $(do_divide 50 5) != 10 ]
+then
+    echo "error in function do_divide"
+    exit 1
+fi
diff --git a/sh/tests/solutions/calculator.sh b/sh/tests/solutions/calculator.sh
new file mode 100755
index 000000000..191d99d31
--- /dev/null
+++ b/sh/tests/solutions/calculator.sh
@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+
+# Unofficial Bash Strict Mode
+set -euo pipefail
+IFS='
+'
+
+number='^-?[0-9]+$'
+
+do_add () {
+    echo $(($1 + $2))
+}
+
+do_sub () {
+    echo $(($1 - $2))
+}
+
+do_mult () {
+    echo $(($1 * $2))
+}
+
+do_divide () {
+    echo $(($1 / $2))
+}
+
+
+if [ $# != 3 ]
+then
+    >&2 echo "Error: expect 3 arguments"
+    exit 1
+elif ! [[ $1 =~ $number && $3 =~ $number ]]
+then
+    >&2 echo "Error: invalid number"
+    exit 4
+else
+    case $2 in
+
+        "+")
+            echo $(do_add $1 $3)
+            ;;
+        
+        "-")
+            echo $(do_sub $1 $3)
+            ;;
+        
+        "*")
+            echo $(do_mult $1 $3)
+            ;;
+        
+        "/")
+            if [ $3 == 0 ]
+            then
+                >&2 echo "Error: division by 0"
+                exit 2
+            fi
+            echo $(do_divide $1 $3)
+            ;;
+        
+        *)
+            >&2 echo "Error: invalid operator"
+            exit 3
+            ;;
+
+    esac
+
+fi
diff --git a/subjects/devops/calculator/README.md b/subjects/devops/calculator/README.md
new file mode 100644
index 000000000..06660678e
--- /dev/null
+++ b/subjects/devops/calculator/README.md
@@ -0,0 +1,96 @@
+## Calculator
+
+### Instructions
+
+In this exercise you will make a script `calculator.sh` that will take 3 arguments, calculate the result and print it on the standard output.
+
+- The first argument and the third argument will be numbers.
+- The second argument will be the operator.
+
+Each operator should have its own function named as follow:
+- `+`: `do_add()`.
+- `-`: `do_sub()`.
+- `*`: `do_mult()`.
+- `/`: `do_divide()`.
+
+Each function will receive two arguments, the left number and the right number, and return the result of the operation.
+
+The functions assume that the input is valid, so the input must be checked before calling the functions.
+
+To choose which function to call you must use the `case` statement.
+
+> The functions will also be tested individually, so it is important to name each function exactly as above, the behavior of the functions have to match the exercise instructions.
+
+### Usage
+
+```console
+$ ./calculator.sh 20 "*" 3
+60
+$ ./calculator.sh 20 / 20
+1
+$ ./calculator.sh -1 - 10
+-11
+$
+```
+
+### Error handling
+
+All errors will print a specific message on **stderr** (ending with a newline) and returns a specific non-zero value:
+- Wrong number of arguments: `"Error: expect 3 arguments"`, returns `1`.
+- Division by 0: `"Error: division by 0"`, exit with `2`.
+- Invalid operator: `"Error: invalid operator"`, exit with `3`.
+- Invalid number(s): `"Error: invalid number"`, exit with `4`.
+
+> Negative numbers are also a valid input.
+
+### Hints
+
+- `case` statement example:
+```sh
+# Check the first argument given to a script
+case $1 in
+    "left")
+        echo "We will turn left"
+        ;;
+    
+    "right")
+        echo "We will turn right"
+        ;;
+    
+    "top")
+        echo "We will turn top"
+        ;;
+    
+    "bottom")
+        echo "We will turn bottom"
+        ;;
+    
+    # Any other case
+    *)
+        # This is printed in stderr
+        >&2 echo "Error: invalid argument"
+        exit 2
+        ;;
+esac
+```
+
+- Example of a function taking two arguments and returning a value by printing it.
+The behavior of this function is the same than the one expected for the operators functions you will create:
+```sh
+print_full_name () {
+    name=$1
+    surname=$2
+    echo $name $surname
+}
+
+print_full_name "Gene" "Mallamar"
+```
+
+> Google and Man will be your friends!  
+
+### References
+
+- [Bash functions](https://linuxize.com/post/bash-functions/)  
+- [Test if a variable is a number](https://stackoverflow.com/questions/806906/how-do-i-test-if-a-variable-is-a-number-in-bash)  
+- [Print on standard error](https://stackoverflow.com/questions/2990414/echo-that-outputs-to-stderr)  
+- [Case statement](https://linuxize.com/post/bash-case-statement/)