While loop until a file exists in bash

Question

I want to write wait until a file exists in bash. How do I do this?

I tried this but it doesnt work:

while [ ! -f outputs\/$trace\_hist_len_$hist_len\_page_size_$page_size\.out]; do
echo "waiting for outputs\/$trace\_hist_len_$hist_len\_page_size_$page_size\.out";
done

It seems to have a syntax error.

Answer 1

while : ; do
    [[ -f "/path/to/file" ]] && break
    echo "Pausing until file exists."
    sleep 1
done

Without using something like inotify, this is about the limit of what you're going to be able to do.

The while loop above just uses : as its conditional which pretty much just means "do it until we kill it."

The important line is the [[ test. The test conditional here does not use the if statement. This is because [[ is an actual command and NOT part of the if statement. This executes [[ -f "/path/to/file" ]] and the && checks the exit status of the [[ command and executes the following statement if that exit status is 0 (success). The following statement here is break which will close out the current loop that your script is in.

Note: In bash it is highly recommended that you use [[ instead of [. It has all of the capabilities of [ but is far more powerful and simple to use.

Answer 2

The space between the file argument and the closing bracket is important.

if [ -f "path" ]; then echo good;fi

if [-f "path"] ; then  echo bad;fi
if [ -f "path"]; then  echo bad;fi
if [-f "path" ]; then  echo bad;fi