Question

Why does not work first and second variants, but third works

    #!/bin/sh
    #---------------------------------------------

    text="my:?text=this:one"
    if (echo $text | grep '^my\:\?text=this\:one') then
        echo "1"
    elif (echo $text | grep '^my:\?text=this:one') then
        echo "2"
    elif (echo $text | grep 'text=this:one') then
        echo "3"
    fi

Answer 1

grep does not use regular expressions by default, add the -E flag to enable extended regular expressions.

Edit: grep does not use extended regular expressions by default, and grep -E is usually aliased to egrep for quicker use