Conditionals

If ... else

if <if-expr>; then
    commands
elif <if-expr>; then
    commands
else
    commands
fi

if <if-expr>; then
    commands
fi

if <if-expr>
then
    commands
fi

• <if-expr> = <Linux command>
• <if-expr> = [ <test-expr> ]

if [ $# -eq 1 ]; then
    echo "There is 1 argument"
fi

if [ $# -eq 1 -a "$1" = "-run" ]; then
    echo "The only argument used was -run"
fi

if [ -e "$1" ]; then
    echo "File exists"
fi

Case statement

case <varname> in
    <value>)
        commands;
        ;;
    *)
        default-commands;
        ;;
esac

• Similar to a switch statement in C/C++ and a case statement in Pascal.

case $choice in
    alpha)
        echo "Choice: alpha"
        ;;
    beta)
        echo "Choice: beta"
        ;;
    *)
        echo "case: default"
        ;;
esac

Select statement

select <varname> in <list of values>; do
    commands;
done

• Prompts the user to make a choice from a list of values.
• Stores the value chosen by the user in the specified variable.

• Redisplays the menu if the user enters an empty line.
• Repeats indefinitely unless an "exit" or "break" command is used.
• Terminates if EOF is read.

select choice in $@; do
    echo "Selection: $choice"
    break
done