wtimestamp

#!/usr/bin/env perl
# wtimestamp (part of ossobv/vcutil) // wdoekes/2015,2019 // Public Domain
#
# Reads lines from stdin and prepends them with the current time.
# Use this for applications that provide output but fail to add a timestamp.
#
# Usage:
#
#   $ application | wtimestamp
#   (outputs stdout from application with a nicely formatted time)
#
# Example:
#
#   $ for x in `seq 3`; do sleep 1.5; echo "line $x"; done | wtimestamp
#   2019-04-12 15:32:39.658942+0200: line 1
#   2019-04-12 15:32:41.161355+0200: line 2
#   2019-04-12 15:32:42.663128+0200: line 3
#
# Previous version, in sh:
#
#  while read -r line; do
#    echo "`date +'%Y-%m-%d %H:%M:%S%z'`: $line"
#  done
#
# Replaced by perl because of all the PID spawning overhead sometimes is
# too much (e.g. when we're monitoring execve's).
#
# See also: tai64n <https://cr.yp.to/daemontools/tai64n.html>
#
use POSIX 'strftime';use Time::HiRes 'gettimeofday';
$|++;my($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;
# It's actually quite horrible that all of the above is needed for a simple
# line-based buffer reading. Surely this could be simpler in perl?
my @v=gettimeofday();
my $f=sprintf '%%Y-%%m-%%d %%H:%%M:%%S.%06d%%z',$v[1];
my $t=strftime($f,,localtime $v[0]);
foreach (@a){$_.="\n";print("$t: $_");}}