wtimedecode

#!/bin/sh
# wtimedecode (part of ossobv/vcutil) // wdoekes/2018 // Public Domain
# Reads 10-digit unix times on stdin and converts them to local time.
#
# Usage:
#
#     $ echo "[$(date +%s)] Some log message" | wtimedecode [--utc]
#     [2018-12-06T14:32:20+0100 (1544103140)] Some log message
#
# The inverse can be done with date(1):
#
#     $ date --date '2018-12-06T11:22:33+0400' +%s | wtimedecode
#     2018-12-06T08:22:33+0100 (1544080953)
#
#exec env LC_ALL=C perl -e '
#use Time::localtime;$|++;sub func{my $s=shift;$us=shift;ctime($s)." ($s$us)";}
#for(<>){s/\b(\d{10})(\.\d+)?/func($1,$2)/e;print}'
exec env LC_ALL=C perl -we '
use strict;use POSIX "strftime";
my ($opt)=@ARGV;my ($tm,$z)=(\&CORE::localtime,"%z");
($tm,$z)=(\&CORE::gmtime,"Z") if $opt and $opt eq "--utc";
sub func{my ($s,$us)=@_;$us="" if not $us;
strftime("%Y-%m-%dT%H:%M:%S".$z,$tm->($s))." ($s$us)";}
$|++;my($prev,$cont,$in)=("",1,"");
while(($cont&&($cont=sysread(STDIN,$in,4096)))||$prev){
my @a=split /\n/s,$prev.$in,-1;$prev=$in="";$prev=pop @a if $cont;
foreach (@a){$_.="\n";
s/\b(\d{10})(\.\d+)?/func($1,$2)/e;
print;}}' -- "$@"