check if argument is a valid date in bash shell

问题:

I am writing a bash shell script in Linux, this program will accept a date (mm-dd-yyyy) as a parameter. I am wondering if there is a simply way to check if the date is valid? is there an operator and I can just use test to check?

回答1:

you can check with date -d "datestring"

so date -d "12/07/2012" is valid, but using hyphen is not valid for bash.

You can also use words: date -d 'yesterday' or date -d '1 week ago' are both valid.

回答2:

You can extract the day, month, and year values from the input date value MM-DD-YYYY and validate it as the unambiguous (ISO) format YYYY-MM-DD instead (you can validate a DD-MM-YYY formatted date as "correct" using date, e.g. 25-12-2010, but it is not a valid MM-DD-YYY date, hence the need to change the date format first)

---

A valid date in the correct format is OK

30th November 2005 is valid:

$ DATE=11-30-2005; d=${DATE:3:2}; m=${DATE:0:2}; Y=${DATE:6:4}; echo "year=$Y, month=$m, day=$d"; if date -d "$Y-$m-$d" &> /dev/null; then echo VALID; else echo INVALID; fi
year=2005, month=11, day=30  
VALID

$ DATE=11-30-2005; if date -d "${DATE:6:4}-${DATE:0:2}-${DATE:3:2}" &> /dev/null; then echo VALID; else echo INVALID; fi
VALID

---

An invalid date in the correct format is NOT OK

31st November 2005 does not validate:

$ DATE=11-31-2005; d=${DATE:3:2}; m=${DATE:0:2}; Y=${DATE:6:4}; echo "year=$Y, month=$m, day=$d"; if date -d "$Y-$m-$d" &> /dev/null; then echo VALID; else echo INVALID; fi
year=2005, month=11, day=31  
INVALID

$ DATE=11-31-2005; if date -d "${DATE:6:4}-${DATE:0:2}-${DATE:3:2}" &> /dev/null; then echo VALID; else echo INVALID; fi
INVALID

---

A valid date in the incorrect format is NOT OK

20th April 1979 in DD-MM-YYYY format does not validate as a MM-DD-YYYY date:

$ DATE=20-04-1979; d=${DATE:3:2}; m=${DATE:0:2}; Y=${DATE:6:4}; echo "year=$Y, month=$m, day=$d"; if date -d "$Y-$m-$d" &> /dev/null; then echo VALID; else echo INVALID; fi
year=1979, month=20, day=04  
INVALID

$ DATE=20-04-1979; if date -d "${DATE:6:4}-${DATE:0:2}-${DATE:3:2}" &> /dev/null; then echo VALID; else echo INVALID; fi
INVALID

---

Alternate simpler method: use BASH variable string replace hyphens to slashes

$ DATE="04-30-2005"; [[ $(date -d "${DATE//-/\/}" 2> /dev/null) ]] && echo VALID || echo INVALID
VALID

$ DATE="04-31-2005"; [[ $(date -d "${DATE//-/\/}" 2> /dev/null) ]] && echo VALID || echo INVALID
INVALID

回答3:

For script use, I kept it as simple as I could. Testing the date value with the date function then checking the exit code of the process.

date -d "02/01/2000" 2>: 1>:; echo $?

This will redirect the standard in and standard error to null : and using echo to return the exit code with $? allows me to check for 0=good date and 1=bad date.

回答4:

The following worked well for me. Many thanks to my co-worker, Tyler Chamberlain, for the OSX solution.

# Validate a given date/time in Bash on either Linux or Mac (OSX).

# Expected date/time format (in quotes from the command line):  YYYY-MM-DD HH:MM:SS
# Example(s):  ./this_script "2012-02-29 13:00:00"   # IS valid
#              ./this_script "2013-02-29 13:00:00"   # Is NOT valid

START_DATETIME=$1

function report_error_and_exit
{
   local MSG=$1
   echo "$MSG" >&2
   exit 1
}

# We can use OSTYPE to determine what OS we're running on.
# From http://stackoverflow.com/questions/394230/detect-the-os-from-a-bash-script

# Determine whether the given START_DATETIME is valid.
if [[ "$OSTYPE" == "linux-gnu" ]]
then
   # Validate the date on a Linux machine (Redhat or Debian).  On Linux, this is 
   # as easy as adding one minute and checking the return code.  If one minute 
   # cannot be added, then the starting value is not a valid date/time.
   date -d "$START_DATETIME UTC + 1 min" +"%F %T" &> /dev/null
   test $? -eq 0 || report_error_and_exit "'$START_DATETIME' is not a valid date/time value. $OSTYPE"
elif [[ "$OSTYPE" == "darwin"* ]]
then
   # Validate the date on a Mac (OSX).  This is done by adding and subtracting
   # one minute from the given date/time.  If the resulting date/time string is identical 
   # to the given date/time string, then the given date/time is valid.  If not, then the
   # given date/time is invalid.
   TEST_DATETIME=$(date -v+1M -v-1M -jf "%F %T" "$START_DATETIME" +"%F %T" 2> /dev/null)

   if [[ "$TEST_DATETIME" != "$START_DATETIME" ]]
   then
      report_error_and_exit "'$START_DATETIME' is not a valid date/time value. $OSTYPE"
   fi
fi

echo "The date/time is valid."

I tested this script on a Red Hat-based system, a Debian-based system and OSX, and it worked as expected on all three platforms. I did not have time to test on Windows (Cygwin).

回答5:

case statements make it easy to support multiple formats and capturing date-parts, i.e.

 case ${date} in
    [0-3][0-9]-[0-1][0-9]-[0-9][0-9][0-9][0-9] )
       yr=...
       mn=...
       dy=... 
    ;;
    [0-1][0-9]-[0-3][0-9]-[0-9][0-9][0-9][0-9] )
       yr=...
       dy=... 
       mn=...
    ;;
    .... other formats
    ;;
    * )
      echo "ERROR on date format, from value=$date, expected formats ..."
      return 1
    ;;     
 esac

I hope this helps.

回答6:

You can use the strptime() function available in Python's time or datetime modules or Perl's Time::Piece module.