Shell Programming and Scripting

Hi,

I found the following biweekly script by searching google:

###############################################
why not schedule it weekly, cache the "date" of the last run to a
file, and then at the beginning of your shell script
compare the current date with the cached date and only approach to the
real code when they are two-week difference.
This logic should be very easy to implement in both cronjob and the
shell script.

Code:

#/bin/sh
 
BASEDIR=/path/to/cron/bin
CACHEFILE=$BASEDIR/lastrun.txt
TODAY=$(date +%F)
DAY14=$(date -d'-14 days' +%F)
 
if ! [ -s "$CACHEFILE" ]; then
date +%F > "$CACHEFILE"
else
LASTRUN=$(<"$CACHEFILE")
if [ "$DAY14" != "$LASTRUN" ]; then
echo "not scheduled"
exit
fi
echo "$TODAY" > "$CACHEFILE"
fi
 echo "program here"

####################################################
This line gives error when i use -x debug option, can someone please help me to fix this?
usage: date [-jnu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ...
[-f fmt date | [[[[[cc]yy]mm]dd]HH]MM[.ss]] [+format]

Thanks
Sincerely,
RM

The options you are trying to use with date aren't supported by all implementations. You can either install AT&T's AST tools which has a date command that does, or install the GNU date which also supports it. I personally would write it this way -- integer math is easier than trying to strip apart a human readable date and adjusting for month/year boundaries.

Code:

#!/usr/bin/env ksh                 
# should also work in bash if you prefer

now=$( date +%s )                                   # current time -- seconds past epoch
nrd=$(( (now - (now % 86400)) + (86400 * 14) ))     # two weeks from today (midnight) -- next run date
cache_file=$HOME/${0%%*/}.next                      # holds date that next run is allowed on
if [[ -f $cache_file ]]
then
    read ok2run <$cache_file
    if (( ok2run > now ))                           # next run date still in future
    then
        echo "abort: hasn't been too weeks; last execution was: $(tail -1 $cache_file)"
        exit 1
    fi
fi
printf "%s\n%s\n" $nrd "$(date)" >$cache_file       # save timestamp of next date ok and date for humans

# continue with rest of script
echo "good to go"       # just for testing/confirmation

It first gets the current time in seconds since the epoch (I believe most date commands support the +%s format, and someone will chime in here if I'm wrong). From there it computes the value of midnight two weeks out -- allowing the script to be run on the same day of the week (two weeks out), any time after midnight.

It uses a cache file to save the next valid execution timestamp, and a human readable string of the last time the command was executed. If there is no file it assumes that it is ok to run.

Hope this was at least some help.

date +%s (seconds since the epoch) is also a GNU extra to the date command.

The simplest way is to work from data +%U (week number in the year). Using mathematics appropriate to your Shell, divide the number by 2 and take the remainder. This gives you 0=odd , 1=even .


When you get anomalies, please post what Operating System and version your are running and what Shell you are using.

agama, methyl - Thanks so much.