+sub modifyconfig {
+ my $f=shift;
+ # the section to modify or add
+ my $targetsection=shift;
+ # fields to change in the section
+ # To remove a field, set its value to "".
+ my %changefields=@_;
+
+ my @lines;
+ my @out;
+
+ if (-e $f) {
+ open(my $in, "<", $f) || die "mr: open $f: $!\n";
+ @lines=<$in>;
+ close $in;
+ }
+
+ my $addfields=sub {
+ my @blanks;
+ while ($out[$#out] =~ /^\s*$/) {
+ unshift @blanks, pop @out;
+ }
+ foreach my $field (sort keys %changefields) {
+ if (length $changefields{$field}) {
+ push @out, "$field = $changefields{$field}\n";
+ }
+ }
+ push @out, @blanks;
+ };
+
+ my $section;
+ while (@lines) {
+ $_=shift(@lines);
+
+ if (/^\s*\#/ || /^\s*$/) {
+ push @out, $_;
+ }
+ elsif (/^\s*\[([^\]]*)\]\s*$/) {
+ if (defined $section &&
+ $section eq $targetsection) {
+ $addfields->();
+ }
+
+ $section=$1;
+
+ push @out, $_;
+ }
+ elsif (/^\s*(\w+)\s*=\s(.*)/) {
+ my $parameter=$1;
+ my $value=$2;
+
+ # continuation line
+ while ($value=~/(.*\\)$/s) {
+ $value=$1."\n".shift(@lines);
+ chomp $value;
+ }
+
+ if ($section eq $targetsection) {
+ if (exists $changefields{$parameter}) {
+ if (length $changefields{$parameter}) {
+ $value=$changefields{$parameter};
+ }
+ delete $changefields{$parameter};
+ }
+ }
+
+ push @out, "$parameter = $value\n";
+ }
+ }
+
+ if (defined $section &&
+ $section eq $targetsection) {
+ $addfields->();
+ }
+ elsif (%changefields) {
+ push @out, "\n[$targetsection]\n";
+ foreach my $field (sort keys %changefields) {
+ if (length $changefields{$field}) {
+ push @out, "$field = $changefields{$field}\n";
+ }
+ }
+ }
+
+ open(my $out, ">", $f) || die "mr: write $f: $!\n";
+ print $out @out;
+ close $out;
+}
+
+# Finally, some useful actions that mr knows about by default.