使用shell脚本中的函数测试文件是否存在

Question

I have the following script, basically a function and an IF

file_exists() {

    if [ -f "$1" ]; then
        return 0
    else
        return 1
    fi
}

if [[ $(file_exists "LICENSE") ]]; then
    echo "YES"
else
    echo "NO"
fi

But this code always returns NO. I know the IF statement expects to get a 0 to be true, but I don't understand why it doesn't work

Answer 1

When using the return value of a function in an if-statement, you do not need to wrap it in [[]] . You can replace

if [[ $(file_exists "LICENSE") ]]; then

with

if file_exists "LICENSE"; then

As for the convention of 0=true and 1=false , it's not preferred to write them out explicitly in return statements . The body of your file_exists function can be reduced to

file_exists() {
    [ -f "$1" ]
}

Answer 2

IMHO if..else redundant here. Use your function like this:

file_exists $FILENAME && echo ok || echo notok