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

You could copy and paste the crontab file into Excel and then create a few functions that do this. Since the time fields are always in the same place, your columns in Excel would correspond to the timeframe in which that command is executed.

You'll have to write your formula so that is accounts for single integer values and repeating values (like 10 versus */10).

If your crobtab file changes a lot and you have many entries, then you could probably write a php script to parse this information pretty quickly.

Answer 2

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.