Getting a [[01: command not found error at the if statement line

Question

For the following script:

for f in $FILES
do

    fname="$(basename "${f}")"
    fn="${fname:6:2}"
    if [["$fn" == "01"]]; then #error here
        echo "yes"
    fi
done

Answer 1

You have a rather simple syntax problem. Just put spaces before and after the test construct, as in

if [[ "$fn" == "01" ]]; then ...

and it should work.

The reason is that the [[ is acually a bash keyword, not an operator, and as such has to be placed "standalone" (similar to the if etc.).

One of your files seems to be called 01. With your syntax, the shell would see the keyword if, which it expects to be followed by a command whose return code is to be evaluated. In your code, it would consider [[01 to be that command, which obviously doesn't exist. That is also the reason for your error message.

If you want to learn more about shell scripting, and since you seem to be using the bash (or ksh) as indicated by your use of the double-bracket test operator, you may want to look into the Bash Guide (as per @terdon's recommendation) and, later, the Advanced Bash scripting guide (once you are "hardened" against the not-so-good practices it sometimes contains) for in-depth information.