Unix Shell Scripts

1. Write a bash shell script that prints “Hello, world” named greet1.sh. Make it executable and run from the command line like so

./greet1.sh

which bash

/bin/bash

cat > greet1.sh <<'EOF'
#!/bin/bash

echo "Hello, world"
EOF

chmod +x greet1.sh

./greet1.sh

Hello, world

2. Write greet2.sh so that it outputs “Hello name” when run from the command line, where name is a command line argument to greet2.sh. Note that name may consist of more than one word e.g. greet2.sh Santa Claus

cat > greet2.sh <<'EOF'
#!/bin/bash

echo "Hello, $@"
EOF

chmod +x greet2.sh

./greet2.sh Santa Claus

Hello, Santa Claus

3. Write greet3.sh so that it asks “What is your name?” when executed, then prints “Hello name” when executed.

Note: This must be run from the terminal, as the notebook cannot accept interactive inputs.

cat > greet3.sh <<'EOF'
#!/bin/bash

echo -n "What is your name? "
read NAME
echo "Hello $NAME"
EOF

chmod +x greet3.sh

4. Write a function mean to calculate the average of numbers given to it as arguments to 4 significant places. For example

mean 1 2  3 4

should output 2.5000.

function mean() {
    sum=0
    n=0
    for x in $@
    do
        n=$((n+1))
        sum=$(echo $sum + $x | bc)
    done
    echo "scale=4; $sum / $n" | bc -l
}

mean 1 2  3 4

2.5000

5. Save the function into a shell scirpt math.sh, and use it in a new bash session (open a second terminal) to find mean 1 2 3 4 as before.

cat > math.sh  <<'EOF'
function mean() {
    sum=0
    n=0
    for x in $@
    do
        n=$((n+1))
        sum=$(echo $sum + $x | bc)
    done
    echo "scale=4; $sum / $n" | bc -l
}
EOF

source math.sh

mean 1 2 3 4

2.5000