dmesg convert timestamps to human format - bash

Question

I have the following sample of dmesg:
throttled log output.
57458] bar 3: test 2 on bar 8 is available
[ 19.696163] bar 1403: test on bar 1405 is available
[ 19.696167] foo: [ 19.696168] bar 3: test 5 on bar 1405 is available
[ 19.696178] foo: [ 19.696179] bar 1403: test 5 on bar 1405 is available
[ 20.928730] foo: [ 20.928733] bar 1403: test on bar 1408 is available
[ 20.928742] foo: [ 20.928745] bar 3: test on bar 1408 is available
[ 24.878861] foo: [ 25.878861] foo: [ 25.878863] bar 1403: bar 802 is present
I would like to convert all timestamps in the line to human format ("%d/%m/%Y %H:%M:%S")
Notes:
This system does not have dmesg -T nor has perl installed.
I would prefer a solution w/ sed or awk, but python is also an option.
I've found a few solutions to this problem, but none quite answers what I need. Nor do I know how to modify it to my needs.
awk -F"]" '{"cat /proc/uptime | cut -d \" \" -f 1" | getline st;a=substr( $1,2, length($1) - 1);print strftime("%d/%m/%Y %H:%M:%S",systime()-st+a)" "$0}'
Or
sed -n 's/\]//;s/\[//;s/\([^.]\)\.\([^ ]*\)\(.*\)/\1\n\3/p' | while read first; do read second; first=`date +"%d/%m/%Y %H:%M:%S" --date="#$(($seconds - $base + $first))"`; printf "[%s] %s\n" "$first" "$second"; done
There's also a python script in here. But outputs some errors which I have zero understanding in.
Thanks!

Answer 1

The following code simulates dmesg -T outcomes. It's inline awk within shell and can be stored as a standalone script or shell function:
awk -v UPTIME="$( cut -d' ' -f1 /proc/uptime )" '
BEGIN {
STARTTIME = systime() - UPTIME
}
match($0, /^\[[^\[\]]*\]/) {
s = substr($0, 2, RLENGTH - 2) + STARTTIME;
s = strftime("%a %b %d %H:%M:%S %Y", s);
sub(/^\[[^\[\]]*\]/, "[" s "]", $0);
print
}
'
It doesn't guarantee precision as dmesg -T provides but makes results a bit closer.

Answer 2

This is a bit touch-and-go, but it should at least give you something to work with:
awk '
{
# tail will be the part of the line that still requires processing
tail = $0;
# Read uptime from /proc/uptime and use it to calculate the system
# start time
"cat /proc/uptime | cut -d \" \" -f 1" | getline st;
starttime = systime() - st;
# while we find matches
while((start = match(tail, /\[[^[]*\]/)) != 0) {
# pick the timestamp from the match
s = substr(tail, start + 1, RLENGTH - 2);
# shorten the tail accordingly
tail = substr(tail, start + RLENGTH);
# format the time to our preference
t = strftime("%d/%m/%Y %H:%M:%S", starttime + s);
# substitute it into the original line. [] are replaced with || so
# the match is not re-replaced in the next iteration.
sub(/\[[^[]*\]/, "|" t "|", $0);
}
# When all matches have been replaced, print the line.
print $0
}' foo.txt