Sometimes we want to compare two directory trees – maybe one is from another system or a backup, and you want to see how they differ. The diff command has a couple of qualifiers that can help:
-rrecurses subdirectories-qonly reports that files are different rather than displaying the differences.
Here’s a typical Apache configuration directory tree from a Debian-based system:
$ tree -d apache2 apache2 ├── conf-available ├── conf.d ├── conf-enabled ├── mods-available ├── mods-enabled ├── sites-available └── sites-enabled
In that directory tree, there are 218 files:
$ ls apache2 | wc -l 218
Let’s assume we have a backup of that directory in apache2-backup, and we want to see what has changed since that backup was taken. We want to see:
- files that have been added
- files that have been removed
- files that have changed
We don’t need to look at all 218 file to find those differences. Instead, we can use diff:
$ diff -rq apache2 apache2-backup Files apache2/apache2.conf and apache2-backup/apache2.conf differ Only in apache2-backup/sites-enabled: wiki.example.com.conf
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