one liner automagic strftime()

[seki]

Hi Monks!

I use often the localtime() / strftime() couple, but while looking at my collection of one-liners tools, I am puzzled by an epoch translator that displays local time without specifying a format.

If I eval the following code,

perl -le'print localtime 1503403724'

the result is not surprisingly

4481422711722331

but the following command line filter

echo 1503403724 | perl -pe's/([\d.]+)/localtime $1/e;'

displays the formated

Tue Aug 22 14:08:44 2017

Is there some untold magic with the inline loop parameter, or with the executable regex?

For the record, the onle-liner is originaly used to translate some log files with a time-stamp on each line in the form of an epoch date instead of a readable date format. Example:

cat var/nagios.log | perl -pe's/([\d.]+)/localtime $1/e;' | less

[hdb]

In the substitution operator the right hand side is evaluated in scalar context and thus localtime returns the formatted date as a string as per documentation:

use strict;
use warnings;

my @x = localtime 1503403724;
print "@x\n";

my $x = localtime 1503403724;
print "$x\n";

my $z = "ccc";
$z =~ s/ccc/wantarray()?"list":"scalar"/e;
print "$z\n";

[seki]

Arf. So no magic, just the list / scalar context. I have always missed that paragraph of the localtime() perldoc... Thanks.

[hdb]

Difficult to say as "Any sufficiently advanced technology is indistinguishable from magic." (Arthur C. Clarke)

Perl surely falls into that category...

[Laurent_R]

Try this:

$ perl -le'print scalar localtime  1503403724'
Tue Aug 22 14:08:44 2017