Find cron jobs that run between given times

Question

Is it possible to find all entries in a crontab that run between time X and time Y without having to parse the cron time entries myself? I'm mainly concerned with time hour and minute, not so much the other 3 time fields.

Answer 1

Anything is possible but you will have to parse crontab yourself.

There are no simple answers, but just because I can here's a partial solution in bash.

    #!/bin/bash

    start="${1-0:0}"
    end="${2-0:0}"
    start_hour=$(cut -d: -f1 <<<"$start")
    end_hour=$(cut -d: -f1 <<<"$end")
    start_min=$(cut -d: -f2 <<<"$start")
    end_min=$(cut -d: -f2 <<<"$end")

    # leading zeroes would be bad
    let start_hour=10#${start_hour}
    let end_hour=10#${end_hour}
    let start_min=10#${start_min}
    let end_min=10#${end_min}

    cat /etc/crontab | \
            grep -v ^\# | \
            grep -E -v '^([a-zA-Z]+)' | \
            awk '{print $1, $2, $7}' | \
    while read line ; do
            if [ ! -z "$line" ] ; then
                    h=$(cut -d' ' -f2 <<<"$line")
                    m=$(cut -d' ' -f1 <<<"$line")
                    cmd=$(cut -d' ' -f3- <<<"$line")

                    if [ "$h" = '*' ] || ( [ $h -ge $start_hour ] && [ $h -le $end_hour ] ) ; then
                            if [ "$m" = '*' ] || ( [ $m -ge $start_min ] && [ $m -le $end_min ] ) ; then
                                    echo $cmd
                            fi
                    fi
            fi
    done

Call like

cron_between 09:00 16:59

This certainly won't work for complex time specifications (e.g. */2) and only reports on the first part of the command. All of this can be corrected, but probably you'd be better off doing it in perl or something.

Answer 2

Since this doesn't seem possible without parsing cron, I decided to write it myself in perl:
(not sure why the formatting is fubar)

#!/usr/bin/perl -w
use strict;
use Set::CrossProduct;

my $begin;
my $end;

if($ARGV[0] && $ARGV[0] =~ /before/i){
    $begin = 0;
    $end = $ARGV[1];

}
elsif($ARGV[0] && $ARGV[0] =~ /after/i){
    $end = 2400;
    $begin = $ARGV[1]; 
}
else{
    $begin = $ARGV[0];
    $end = $ARGV[1];
}

if(!defined($begin) || !defined($end)){
    print STDERR "Invalid Arguments\n";
    exit 1;
}

my @crontab = `crontab -l`;

foreach my $cronjob (@crontab){
    chomp $cronjob;

next if $cronjob =~ /^ *\#/ ||$cronjob =~ /^ *$/  ;

#print "in: $cronjob\n";

my ($min,$hour,$day_of_month,$month,$day_of_week, @cmd) = split(/ /, $cronjob);

my @mins = expandRange($min,0,59);
my @hours = expandRange($hour,0,23);

my $cp = Set::CrossProduct->new([\@hours,\@mins]);

my $combos = $cp->combinations();

foreach my $time ( map { $_->[0]*100 + $_->[1] } @$combos){
if($time >= $begin && $time <= $end){
    print $cronjob,"\n";
    last; #don't print the job n times, just once
}
}


}

sub expandRange{

my ($in,$begin,$end) = @_;
#print "in: ($in)[$begin:$end]\n";
my @range;

my @vals = split(/,/,$in);
foreach my $val (@vals){
my $mult = 1;
if($val =~ /\/(.+)$/){
    $mult = $1;
    $val =~ s/\/(.+)//;
}

if($in =~ /\*/){
    @range = grep { $_ % $mult == 0 && $_ >= $begin &&  $_ <= $end  } $begin..$end;
}
elsif($val =~ /[\-:]/){
    my ($first, $last) = split(/[\-:]/,$val);
    push(@range, grep {  $_ % $mult == 0 && $_ >= $begin &&  $_ <= $end } $first..$last);
}
elsif($val >= $begin &&  $val <= $end) {
    push(@range, $val);
}
}

my %unique;
@unique{@range} = 1;

return sort keys %unique;


}