Insert a line at the end of an ini section only if it doesn't exist - awk

Question

I have an smb.conf ini file which is overwritten whenever edited with a certain GUI tool, wiping out a custom setting. This means I need a cron job to ensure that one particular section in the file contains a certain option=value pair, and insert it at the end of the section if it doesn't exist.
Example
Ensure that hosts deny=192.168.23. exists within the [myshare] section:
[global]
printcap name = cups
winbind enum groups = yes
security = user
[myshare]
path=/mnt/myshare
browseable=yes
enable recycle bin=no
writeable=yes
hosts deny=192.168.23.
[Another Share]
invalid users=nobody,nobody
valid users=nobody,nobody
path=/mnt/share2
browseable=no
Long-winded solution using awk
After a long time struggling with sed, I concluded that it might not be the right tool for the job. So I moved over to awk and came up with this:
#!/bin/sh
file="smb.conf"
tmp="smb.conf.tmp"
section="myshare"
opt="hosts deny=192.168.23."
awk '
BEGIN {
this_section=0;
opt_found=0;
}
# Match the line where our section begins
/^[ \t]*\['"$section"'\][ \t]*$/ {
this_section=1;
print $0;
next;
}
# Match lines containing our option
this_section == 1 && /^[ \t]*'"$opt"'[ \t]*$/ {
opt_found=1;
}
# Match the following section heading
this_section == 1 && /^[ \t]*\[.*$/ {
this_section=0;
if (opt_found != 1) {
print "\t'"$opt"'";
}
}
# Print every line
{ print $0; }
END {
# In case our section is the very last in the file
if (this_section == 1 && opt_found != 1) {
print "\t'"$opt"'";
}
}
' $file > $tmp
# Overwrite $file only if $tmp is different
diff -q $file $tmp > /dev/null 2>&1
if [ $? -ne 0 ]; then
mv $tmp $file
# reload smb.conf here
else
rm $tmp
fi
I can't help feeling that this is a long script to achieve a simple task. Is there a more efficient/elegant way to insert a property in an ini file using basic shell tools like sed and awk?

Answer 1

Consider using Python 3's configparser:
#!/usr/bin/python3
import sys
from configparser import SafeConfigParser
cfg = SafeConfigParser()
cfg.read(sys.argv[1])
cfg['myshare']['hosts deny'] = '192.168.23.';
with open(sys.argv[1], 'w') as f:
cfg.write(f)
To be called as ./filename.py smb.conf (i.e., the first parameter is the file to change).
Note that comments are not preserved by this. However, since a GUI overwrites the config and doesn't preserve custom options, I suspect that comments are already nuked and that this is not a worry in your case.

Answer 2

Untested, should work though
awk -vT="hosts deny=192.168.23" 'x&&$0~T{x=0}x&&/^ *\[[^]]+\]/{print "\t\t"T;x=0}
/^ *\[myshare\]/{x++}1' file

Answer 3

This solution is a bit awkward. It uses the INI section header as the record separator. This means that there is an empty record before the first header, so when we match the header we're interested in, we have to read the next record to handle that INI section. Also, there are some printf commands because the records still contain leading and trailing newlines.
awk -v RS='[[][^]]+[]]' -v str="hosts deny=192.168.23." '
{printf "%s", $0; printf "%s", RT}
RT == "[myshare]" {
getline
printf "%s", $0
if (index($0, str) == 0) print str
printf "%s", RT
}
' smb.conf
RS is the awk variable that contains the regex to split the text into records.
RT is the awk variable that contains the actual text of the current record separator.

Answer 4

With GNU awk for a couple of extensions:
$ cat tst.awk
index($0,str) { found = 1 }
match($0,/^\s*\[([^]]+).*/,a) {
if ( (name == tgt) && !found ) { print indent str }
name = a[1]
found = 0
}
{ print; indent=gensub(/\S.*/,"","") }
.
$ awk -v tgt="myshare" -v str="hosts deny=192.168.23." -f tst.awk file
[global]
printcap name = cups
winbind enum groups = yes
security = user
[myshare]
path=/mnt/myshare
browseable=yes
enable recycle bin=no
writeable=yes
hosts deny=192.168.23.
[Another Share]
invalid users=nobody,nobody
valid users=nobody,nobody
path=/mnt/share2
browseable=no
.
$ awk -v tgt="myshare" -v str="fluffy bunny" -f tst.awk file
[global]
printcap name = cups
winbind enum groups = yes
security = user
[myshare]
path=/mnt/myshare
browseable=yes
enable recycle bin=no
writeable=yes
hosts deny=192.168.23.
fluffy bunny
[Another Share]
invalid users=nobody,nobody
valid users=nobody,nobody
path=/mnt/share2
browseable=no