Shell and handling dates

jcookeman · 07-30-2008, 11:30 AM

I have some scripts that take a date as an optional parameter. It's now becoming necessary to actually do some sanity checking on that date as it is required to be in a strict format. I've come up with the following pretty quick, but wonder if you guys have anything like this or a more clever way. The following does check for future dates and invalid dates such as Feb 29 on non-leap year.

Code:

#!/bin/env bash

shopt -s -o nounset

DDMMYY=${1-'today'}
HHMMSS=${2-'09:00'}

# Returns:
# 0 - valid date
# 1 - Future date
# 2 - Invalid date
check_date()
{
   { DATE="`date -d "$1 $2" +%s`" || return 2
     NOW="`date +%s`"
   } >>/dev/null 2>&1
     [[ "$DATE" -lt "$NOW" ]] && return 0 || return 1
}

# Returns: 
# Exit code of `date`
# Sets FMT_DATE to formatted date "DD-Mon-YY HH:MM:SS"
get_fmt_date()
{
     FMT_DATE="`date -d "$1 $2" +"%d-%b-%y %T"`"
     return $?
}

check_date $DDMMYY $HHMMSS || exit $?
get_fmt_date $DDMMYY $HHMMSS
echo $FMT_DATE

Example usage:

Code:

[jc@centosvm ~]$ ./test_date.sh 
30-Jul-08 09:00:00
[jc@centosvm ~]$ ./test_date.sh 2/29/08
29-Feb-08 09:00:00
[jc@centosvm ~]$ ./test_date.sh 2/29/08 1031
[jc@centosvm ~]$ ./test_date.sh 2/29/08 10:31
29-Feb-08 10:31:00
[jc@centosvm ~]$ ./test_date.sh 2/29/09
[jc@centosvm ~]$

Mr. C. · 07-30-2008, 01:09 PM

Nice.

This line (and others like it) is a little convoluted:

DATE="`date -d "$1 $2" +%s`"

Use either of the simpler:

DATE=$(date -d "$1 $2" +%s)
DATE=`date -d "$1 $2" +%s`

Consider placings braces around your compound logic groupings for clarity (who remembers precedence?)

{ [[ "$DATE" -lt "$NOW" ]] && return 0 ; } || return 1

You can't really append to the bit bucket:

>>/dev/null 2>&1 # appending is superfluous

> /dev/null 2>&1 # simple redirection is sufficient