Unix/Lunix Programming

Exercise 1

Read the following script read_validate and answer the questions.

read -p "Enter a single item > "

# is input a valid filename?

if [[ $REPLY =~ ^[-[:alnum:]\._]+$ ]]; then

echo "'$REPLY' is a valid filename."

if [[ -e $REPLY ]]; then

echo "And file '$REPLY' exists."

else

echo "However, file '$REPLY' does not exist."

fi

# is input a floating point number?

if [[ $REPLY =~ ^-?[[:digit:]]*\.[[:digit:]]+$ ]]; then

echo "'$REPLY' is a floating point number."

else

echo "'$REPLY' is not a floating point number."

fi

# is input an integer?

if [[ $REPLY =~ ^-?[[:digit:]]+$ ]]; then

echo "'$REPLY' is an integer."

else

echo "'$REPLY' is not an integer."

fi

else

echo "The string '$REPLY' is not a valid filename."

fi

What is the meaning of the command [[ "$REPLY" =~ ^[-[:alnum:]\._]+$ ]] ?

What is the meaning of the command [[ $REPLY =~ ^-?[[:digit:]]*\.[[:digit:]]+$ ]] ?

If the script is executed and a user provides --123.0 as the input, what shall be the output of the program?

If the script is executed and a user provides 0.0 as the input, what shall be the output of the program?

If the script is executed and a user provides -0. as the input, what shall be the output of the program?

If the script is executed and a user provides 012 as the input, what shall be the output of the program?