LighthouseJ has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to find the difference in seconds between two dates. The two (and only two) dates come as standard out like: 
Sun 09 30 06 42 36 2007
Tue 10 02 06 01 55 2007

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(Note: the months correspond to September and October respectively.)

I tried to do this with awk because I use awk in plenty of other places but awk's mktime() is a GNU-only addition it seems and I only have access to barebones Solaris installs. The only alternative remaining I think is Perl's timelocal function in Time::Local which I believe is a part of the standard install, right? My goal is to put a Perl one-liner in a sh script and this is the last piece in the pipe. I've already written a Perl script which works but purely as an exercise for the monkish community, where are the improvements I'm missing?

Here's what I have currently but I am actively working on it though: 
my @array;
while (<>) {
    chomp;
    my @fields = split;
    shift @fields;
    unshift(@fields, pop(@fields));
    $fields[1]--; # decrement the month, timelocal is zero-based
    push (@array, timelocal (reverse @fields));
}

print $array[1] - $array[0];

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"The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why." -- `man perl`

Replies are listed 'Best First'.
Re: Diff'ing dates
by ikegami (Patriarch) on Oct 02, 2007 at 13:33 UTC 
    perl -MTime::Local -lane"END{print$t[1]-$t[0]}$F[1]--;push@t,timelocal
+@F[5,4,3,2,1,6]"

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    Update: 

    perl -MTime::Local -lane"END{print$t}$F[1]--;$t+=($.*2-3)*timelocal@F[
+5,4,3,2,1,6]"

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[d/l]
[select]
      Using your inspiring one-liner, I morphed my script with yours and came up with this:

      /bin/perl -MTime::Local -ne '{$t[1]-- && push(@epochs,timelocal(@t[5,4,3,2,1,6])) if (@t=split)} END { print $epochs[1] - $epochs[0]; }'

      The END block is most likely what will change because the value of the diff will be used to determine exit status.

      Thanks a lot for the fresh perspective, it was very helpful.

      "The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why." -- `man perl`
[reply]
[d/l]

        The exit code can be controled as follows: 

        END { exit 1+($epochs[0] <=> $epochs[1]) }

        [download]
        0: first time is earlier
1: both times are the same
2: second time is earlier

        [download]
        perl -MTime::Local -lane'END{exit 1+($d<=>0)}$F[1]--;$d+=($.*2-3)*time
+local@F[5,4,3,2,1,6]'

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[d/l]
[select]
      I tried the command and this is what I got: 
      $ echo -e "Sun 09 30 06 42 36 2007\nTue 10 02 06 01 55 2007\n" | perl 
+-MTime::Local -lane"END{print$t}$F[1]--;$t+=($.*2-3)*timelocal@F[5,4,
+3,2,1,6]"
Can't modify single ref constructor in postdecrement (--) at -e line 1
+, near "]--"
syntax error at -e line 1, near "+="
Execution of -e aborted due to compilation errors.

      [download]
      "The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why." -- `man perl`
[reply]
[d/l]
        Use single quotes on UNIX-like operating systems: 
        echo -e "Sun 09 30 06 42 36 2007\nTue 10 02 06 01 55 2007\n" | \
perl -MTime::Local -lane 'END{print$t}$F[1]--;$t+=($.*2-3)*timelocal@F
+[5,4,3,2,1,6]'

        [download]

        Double quotes cause your shell to interpret e.g. $t as a shell variable.

        --shmem 

        _($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}
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[d/l]
[select]
        Use the appropriate quotes for your shell. Switch double quotes for single quotes.
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