Capturing user input in Bash

We use read to gather user input.

Capturing raw inputs

# Wait for the input
echo "What is your name?"
read name

# Silently gather the input and proceed (the input won't show up in the terminal)
echo "What is your password?"
read -s pass

# Combine in single line
read  -p "What's your favourite animal? " animal

echo name: $name, pass $pass, animal: $animal

Offering a selection

We can use select to get the user to choose from a series of options.

select animal in "bird" "dog" "cow"
do
    echo "You selected $animal"
    break
done

This will present each option as number that can be inputted:

1) bird
2) dog
3) cow
#? 1
You selected bird

We could make this more robust by using a case statement:

select animal in "bird" "dog" "cow"
do
    case $animal in
        bird) echo "Birds like to tweet";;
        dog) echo "Dogs like to woof";;
        cow) echo "Cows like to moo";;
        quit) break;;
        *) "I'm not sure what that means"
    esac
done

Ensuring you capture a valid response from the user

Set a default response value with `-i`

If the user doesn't enter anything, the value will be set to the default.

read -ep "Favourite colour? " -i "blue" favecolour
echo "$favecolour"
# blue

Alternative formulation:


read -p "Favourite colour? [blue]" fave

# If response empty...
if [[ -z $fave ]]; then
    fave="blue"
fi
echo "$fave was selected"

Check right number of arguments supplied

Here we test that the right number of arguments have been passed to the script:

if (( $#<3 )); then
    echo "This command requires three arguments:"a
    echo "username, userId, and favouriteNumber"
else
    echo "username: $1"
    echo "userid: $2"
    echo "favourite number: $3"
fi

Check the response is valid

The following example demonstrates checking an input for a pattern (a data-link integer sequence):

read -p "Which year? [nnnn] " year
until [[ $year =~ [0-9{4} ]];
    read -p "A four-digit year, please! [nnnn] " year
done
echo "Selected year: $year"

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