Command not found Error (stderr) while comparing string in Bash Script [duplicate]

问题

This question already has answers here:

bash, command not found [duplicate] (2 answers)

Closed 5 years ago.

Problem is to read one character from the user (this may be 'Y', 'y', 'N', 'n'). If the character is Y or y display YES. If the character is N or n display NO.

Original Problem

Here's my code:

read option
if ["$option"=="y"] || ["$option"=="Y"]
then
    echo "YES"
else
    echo "NO"
fi

It throws an Error (stderr)

solution.sh: line 2: [Y=y]: command not found
solution.sh: line 2: [Y=Y]: command not found

回答1:

read option
if [ "$option" == "y" ] || [ "$option" == "Y" ]
then
echo "YES"
elif [ "$option" == "n" ] || [ "$option" == "N" ]   
then
echo "NO"
else
echo "?"
fi

回答2:

Leave space before ] and after [ in if statement.. if [ "$option"="y" ] || [ "$option"="Y" ]

回答3:

You can use this in BASH:

[[ "$option" == [Yy] ]] && echo "YES" || echo "NO"

来源：https://stackoverflow.com/questions/27222542/command-not-found-error-stderr-while-comparing-string-in-bash-script