What's the most elegant way to add Redis to /etc/services? - shell

Question

So today, April 23rd 2015, the Internet Assigned Numbers Authority had decreed the use of port 6379 to Redis, a frabjous day indeed!
I wish to com·mem·o·rate this splendid occasion by adding the following line to my /etc/services file:
redis 6379/tcp
What would be the best way to go about it? By best I mean, of course, the following:
Needless to say, the new line should be inserted in its proper place (i.e.g. under the Assigned Numbers block, right after gnutella-rtr 6347/udp on my system)
I've considered the use of various text editors, but it feels out of place
Ideally, the solution should be a copy-pastable one-liner
I can envision the awk script that could do that but I'm looking for something more, a certain je ne sais quoi
Update re #Markus' sed proposal: I'm afraid the problem would be applying this "patch" on other systems that do not necessarily have the same /etc/services file so, expanding on point #1 above, the solution must ensure that regardless the specifics of to-be-preceding service in the file, order is kept.
Update 2: a few points that seem important to state - a) while not mandatory, the solution's length (or lack of rather) is certainly an important part of its elegance (similarly for external dependencies [i.e. lack of these]); b) I/we assumed that /etc/services is sorted, but it would be interesting to see what happens when it isn't; c) assume that you have root privileges and be careful with that rm / -rf command.

Answer 1

A single line sort that puts it in the right place:
echo -e "redis\t\t6379/tcp" | sort -k2 -n -o /etc/services -m - /etc/services

Answer 2

Nothing in the rules against answering my own question - this one uses Redis exclusively:
cat /etc/services | redis-cli -x SET services; redis-cli --raw EVAL 'local s = redis.call("GET", KEYS[1]) local b, p, name, port, proto; p = 1 repeat b, p, name, port, proto = string.find(s, "([%a%w\-]*)%s*(%d+)/(%w+)", p) if (p and tonumber(port) > tonumber(ARGV[2])) then s = string.sub(s, 1, b-1) .. ARGV[1] .. "\t\t" .. ARGV[2] .. "/" .. ARGV[3] .. "\t\t\t# " .. ARGV[4] .. "\n" .. string.sub(s, b, string.len(s)) return s end until not(p)' 1 services redis 6379 tcp "remote dictionary server" > /etc/services
Formatted Lua code:
local s = redis.call("GET", KEYS[1])
local b, p, name, port, proto
p = 1
repeat
b, p, name, port, proto = string.find(s, "([%a%w\-]*)%s*(%d+)/(%w+)", p)
if (p and tonumber(port) > tonumber(ARGV[2])) then
s = string.sub(s, 1, b-1) .. ARGV[1] .. "\t\t" .. ARGV[2]
.. "/" .. ARGV[3] .. "\t\t\t# " .. ARGV[4] .. "\n"
.. string.sub(s, b, string.len(s))
return s
end
until not(p)
Note: a similar challenge (https://gist.github.com/jorinvo/2e43ffa981a97bc17259#gistcomment-1440996) had inspired this answer. I chose a pure Lua script approach instead of leveraging Sorted Sets... although I could :)

Answer 3

An idempotent awk one-liner that inserts 6379 in order would be:
awk -v inserted=0 '/^[a-z]/ { if ($2 + 0 == 6379) { inserted=1 }; if (inserted == 0 && $2 + 0 > 6379) { print "redis\t\t6379/tcp"; inserted=1 }; print $0 }' /etc/services > /tmp/services && mv /tmp/services /etc/services

Answer 4

Real men don't use sed/awk :)
TMP_SERVICES=/tmp/services.$RANDOM
while read line
do
printf %b "$line\n" >> $TMP_SERVICES
if [[ $line == *"6347/udp"* ]]; then
printf %b "redis\t\t6379/tcp\n" >> $TMP_SERVICES
fi
done<"/etc/services"
mv -fb $TMP_SERVICES /etc/services

Answer 5

How about a python script, Itamar?
It works on the notion of extracting the port number (called the index in the code) and if we are above 6378 but have not yet printed our Redis line, print it, then mark that sentinel true and just print all lines (including the one we are on) after.
#!/usr/bin/python
lines = open("/etc/services").readlines()
printed=False
for line in lines:
if printed:
print line.rstrip()
continue
datafields = line.split()
if line[0] == "#":
print line.rstrip()
else:
datafields = line.split()
try:
try:
index,proto = datafields[1].split("/")
index = int(index)
except:
index,proto = datafields[0].split("/")
index = int(index)
if index > 6378:
if not printed:
print "redis 6379/tcp #Redis DSS"
printed = True
print line.rstrip()
except:
print datafields
raise
The relevant section on my file for comparison:
gnutella-rtr 6347/tcp # gnutella-rtr
# Serguei Osokine <osokin#paragraph.com>
# 6348-6381 Unassigned
redis 6379/tcp #Redis DSS
metatude-mds 6382/udp # Metatude Dialogue Server
metatude-mds 6382/tcp # Metatude Dialogue Server
Notice the line above Redis is a range. Short of breaking the range this is a workable solution for me. You could break the range but IMO this works just fine. Splitting the range seems a bit much for a simple, elegant script. Especially considering the likelihood most services files don't have the unassigned ranges listed (this is on OS X) - and that they are in a comment anyway.
UPDATE
If you don't care about the local file and it's comments, this gets you all currently assigned ports which are not Reserved or Discard-ed:
curl -s http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv| awk -F',' '$4!~/(Discard|Unassigned|Reserved)/ && $1 && $2+0>0 && $1!~/FIX/ {printf "%-16s\t%s/%s\t#%s\n", $1,$2,$3,$4}' > /etc/services
The FIX test is because some of those lines have embedded newlines - which can be a pain in awk.

Answer 6

sed -i '/6347\/udp/a redis 6379\/tcp' /etc/services
good luck!
update
sed -i '/6347\/udp/a redis \t\t 6379\/tcp' /etc/services
looks better ...
update 2
lol
sed -i ''"$(echo $(echo $(grep -n $(awk {'print$2'} /etc/services | awk -F "/" '$1<6379'{'print$1'} | tail -1) /etc/services | awk -F ':' {'print$1'}|tail -1) + 1)|bc)"'i redis \t\t 6379\/tcp' /etc/services

Answer 7

I like the in-place subsitution of sed, so I combine it with an awk search of the next line in services
R="redis\t\t6379/tcp\t\t\t# data structure server" N=$(awk '{if($2+0 == 6379) exit(1);if ($2+0 > 6379) {print $0;exit(0)}}' /etc/services) && sed -i "s~$N~$R\n$N~" /etc/services