Updating an INI file with AWK

The problem is simple: update a specific line in a specific section of a .ini file in a shell script. The file (a configuration file for Gitosis) looks something like this:

[gitosis]


[repo repo1]
description = This is a repository with stuff in it
owner = A User

[repo repo2]
description = Another repository with stuff in it
owner = Another User

[repo docs]
description = Documentation
owner = A Manager

[group developers]
writable = repo1 repo2 docs
members = auser anotheruser

[group managers]
writable = docs
readonly = repo1

The goal is to append a value to the writable line in the group developers section (leaving the rest of the lines alone). Any solution will need to do the following:

1. find the group developers section; then
2. find the writable line in that section, if any, and update it.

This is simple to do in AWK:

1. a rule sets a flag when you enter the group developers section;
2. another updates the writable line when the flag is set;
3. a thirds rule clears the flag when you leave the section;
4. a final rule outputs other lines unchanged (we use a flag to skip the lines modified and output above).

Here's the code:

# Clear the flag
BEGIN {
    processing = 0;
}

# Entering the section, set the flag
/^\[group developers/ {
    processing = 1;
}

# Modify the line, if the flag is set
/^writable = / {
    if (processing) {
        print $0" foo";
        skip = 1;
    }
}

# Clear the section flag (as we're in a new section)
/^\[$/ {
    processing = 0;
}

# Output a line (that we didn't output above)
/.*/ {
    if (skip)
        skip = 0;
    else
        print $0;
}

Easy!