How to do something with Bash when a text line appears in a file

Question

I want to run a command as soon as a certain text appears in a log file. How do I do that in Bash?

Accepted Answer

Use command

```
tail -f file.log | grep --line-buffered "my pattern" | while read line
do
  echo $line
done
```

The `--line-buffered` is the key here, otherwise the read will fail.

Solution