isdate(USP)

Name

isdate : Checks an 8-digit date

Synopsis

Usage   : isdate <date>

Version : Mon Jan 17 11:50:14 JST 2022

Edition : 1

Description

Checks if the 8-digit date passed as <date> is a valid date.  If it

is, the command exits normally, otherwise the command exits with an

error (exit status 1).

Example

$ isdate 20090101

$ echo $?

0

$ isdate 20090199

$ echo $?

1

Note

Leap Years

  Years divisible by 4 are leap years. (February has 29 days)

  Years divisible by 100 are not leap years. (February has 28 days)

  Years divisible by 400 are leap years. (February has 29 days)

Known Issues

September 1752 is missing 11 days from the 3rd to the 13th, however

this command does not cause an error for these dates.  These days

were removed when converting from the Julian calendar to the

Gregorian calendar. ("$ cal 9 1752" is used for confirmation.)

# 20230609 takahashi modify from "13 days from the 3rd to the 15th" to "11 days from the 3rd to the 13th" in <Known Issues>