tee results in a null file

Question

I try to change Apache configuration with this:

sudo awk '/<Directory \/var\/www\/>/,/AllowOverride None/{sub("None", "All",$0)}{print}' /etc/apache2/apache2.conf | sudo tee /etc/apache2/apache2.conf > /dev/null

After this /etc/apache2/apache2.conf is empty. If I change the destination file to ~/apache2.conf for example, the output is correct.

Why?

Answer 1

You are referencing the same file twice in the pipeline, tee will overwrite the file before awk gets to it. Either use a temporary file or use sponge from moreutils.

Recent versions of GNU awk, 4.1.1, have a -i inplace argument which simulates editing file in-place:

Answer 2

That your awk/tee adventure does not work reliably, which has already been said here. ;)

You could try another way:

_drum-roll

Use the power of perl!

^{again drum-roll}

sudo perl -i.bak -0777pe 's/(<Directory \/var\/www\/>([^<].*\n)*.*AllowOverride\s)None/$1All/' /etc/apache2/apache2.conf

• -i.bak

  in-place edit and create a backup /etc/apache2/apache2.conf.bak

• -0777

  slurps the whole file at once

---

Example

Input file

cat foo

<Directory /var/www/>
    foo bar
    AllowOverride None
</Directory>


<Directory /var/www1/>
        AllowOverride None
</Directory>

The command

perl -i.bak -0777pe 's/(<Directory \/var\/www\/>([^<].*\n)*.*AllowOverride\s)None/$1All/' foo 

The content in the file after starting the command

cat foo

<Directory /var/www/>
    foo bar
    AllowOverride All
</Directory>


<Directory /var/www1/>
        AllowOverride None
</Directory>