Tweak perl script for human-readable dmesg output

Question

In RHEL 6 I have the kernel parameter:

printk.time=1

So that my dmesg would have a timestamp. However it shows in seconds from restart, like this:

[12.23456]

I found a script that you place inside .bashrc that converts the seconds to HR date.

dmesg_with_human_timestamps () {
$(type -P dmesg) "$@" | perl -w -e 'use strict;
    my ($uptime) = do { local @ARGV="/proc/uptime";<>}; ($uptime) = ($uptime =~ /^(\d+)\./);
    foreach my $line (<>) {
        printf( ($line=~/^\[\s*(\d+)\.\d+\](.+)/) ? ( "[%s]%s\n",  scalar localtime(time - $uptime + $1), $2 ) : $line )
    }'
}
alias dmesg=dmesg_with_human_timestamps

This works great and my dmesg output now looks like this:

[Fri Jun 10 13:07:14 2016]

But how can I change the code to make that look like this:

[2016/06/10 13:25:28]

Answer 1

The POSIX module includes the strftime function, which allows via strftime(3) conversion specifier characters the desired templating of time:

% perl -MPOSIX=strftime -E 'say strftime "[%F %T]", localtime(time)'
[2011-02-17 10:55:37]
%

So in your case make it perl -MPOSIX=strftime -e ... and then

printf( ($line=~/^\[\s*(\d+)\.\d+\](.+)/) ? ( "[%s]%s\n", strftime("%F %T", localtime(time - $uptime + $1)), $2 ) : $line )

You may need the more verbose %Y-%m-%d %H... template if your strftime(3) lacks %F, see strftime(3) for details.