I'm trying to understand why the following Bash loop doesn't exit on its first iteration, even though I expect it to. Here's the code I'm using:
```bash
while read -r line
do
echo "$line"
done < file.txt
```
From what I see, `read -r line` should fail if there's nothing to read, right? But it seems like it doesn't break immediately when running the script. Can someone explain why this happens?
2 Answers
The confusion comes from how the `read` command works. The `-r` option prevents it from interpreting backslashes as escape characters. So `line` captures whatever is read from stdin, which is redirected from `file.txt`. If your file contains any content (even a blank line), the `read` command will succeed since it finds a newline character, and therefore, the loop continues. If `file.txt` is truly empty, the loop won't even start, and you won't see any output. You might want to check if there's an actual empty line in your file or if it's completely blank.
It seems like you expect `read` to fail when it has nothing to read, but it actually prepares the environment first and opens the file as soon as the loop starts. Bash will check for EOF, not until after attempting to read. If `file.txt` has any whitespace or hidden characters, `read` will succeed and the loop will continue. To test this, you can print the file's contents using `cat -A file.txt` to see if there's something unexpected in there!
Thanks for the insight! I'll check the file closely to see what's going on.