[SOLVED] Alternative way of sed range substitution in busybox sed or awk

Issue

Given following (part of) olsrd.conf file, I want to set single settings with sed or awk (however possible) within busybox.

LoadPlugin "olsrd_httpinfo.so.0.1" {
  # defaults to 1978
  #PlParam "Port"   "8080"
  # if you dont set these, the default is to listen only on the loopback device
  #PlParam "Host"   "80.23.53.22"
  #PlParam "Net"    "10.0.0.0 255.0.0.0"
  #PlParam "Net"     "0.0.0.0 0.0.0.0"
  #PlParam "Host"   "127.0.0.1"
}

LoadPlugin "olsrd_txtinfo.so.1.1" {
  #PlParam "port"   "2006"
  #PlParam  "accept" "0.0.0.0"
}

LoadPlugin "olsrd_jsoninfo.so.1.1" {
  #PlParam "port"   "9090"
  #PlParam  "accept" "0.0.0.0"
}

Using GNU sed this works quite well in usual Linux distros with following example:

MYPORT="1234"
sed -e "/^LoadPlugin.*olsrd_txtinfo.*/ , /}/ s/.*PlParam.*port.*$/PlParam \"port\" \"$MYPORT\"/I" olsrd.conf

But in busybox (v1.33.1) this gives error: sed: unsupported command ,

As far as I understand, busybox sed does not support ranges, thus this error message.

Is there an alternative to accomplish that with busybox sed or else maybe with busybox awk?

Solution

Besides removing the spaces around the , operator that are the culprint here, I suggest tweaking the regex a bit more:

• The .* at the end of the first matching line detecting pattern is redundant
• The -e is redundant here
• $ after the last .* in the subsitution command is redundant (.* already matches the whole line (string, in fact)
• If you use single quotes around the sed command, you would not have to worry about how to escape double quotation marks later. Only double-quote the variable part, and keep the rest in single quotes
• Also, if you capture the initial whitespace on the line with #PlParam (using ^\([[:space:]]*\)), you can keep the indentation (using \1 backreference in the replacement).

So, you can use

sed '/^LoadPlugin.*olsrd_txtinfo/,/}/ s/^\([[:space:]]*\).*PlParam.*port.*/\1PlParam "port" "'"$MYPORT"'"/I' olsrd.conf

See the online demo.

Answered By - Wiktor Stribiżew

Answer Checked By - Clifford M. (WPSolving Volunteer)