How is this awk command working across multiple lines?

Question

I'm confused by a portion of the below command.

awk '/<Directory \/>/,/AllowOverride None/{sub("None", "All", $0)}{print}' /etc/apache2/apache2.conf > myfile.txt

The command replaces

<Directory />
    AllowOverride None
</Directory>

with

<Directory />
    AllowOverride All
</Directory>

in the Apache configuration, and writes the updated configuration to myfile.txt.

I don't understand how the command is pattern matching across two lines of the file. None of the examples that I've been able to find work across lines. I'm guessing it has something to do with the comma in /<Directory /\>,/AllowOverride, but I'd like to understand exactly what's going on. How is this pattern match being done across two lines of the file?

Also, why is {print} necessary? Doesn't awk print its results by default?

Answer 1

• within /<Directory \/>/,/AllowOverride None/ (between those lines)
• sub( ... ) will substitute None for All
• a {print} is needed for all lines (substituted or not)

Note that line(s) with AllowOverride None will get a sub and a print, all other line will be printed only.

sample file:

<Directory />
   ## we don't want None
    AllowOverride None
   ## all or None-thing
</Directory>

will become

<Directory />
   ## we don't want All
    AllowOverride All
   ## all or None-thing
</Directory>

about default, consider

... | awk 'NF==7' 

which will by default print lines with 7 fields, however, in your case, sub function overwrite default, so no other action will be taken. That is why you need an explicit print (if you remove explicit print, nothing will be outputed).