Check a user's input is correctly formatted

Question

I'm trying to validate a user's input when they enter a date into my bash script.

The correct format should be YYYY-MM-DD HH:MM:SS

What I have so far is this, but it's not quite right.

read -p "-" datetime
if [[ $datetime ! "*[^2000-2100]-[^01-12]-[^10-31] [^00-24]:[^00-60]:[^00-60]*" ]]
  then
    echo "Not a date"
fi

Hmmm... 2100-02-31 24:60:60 doesn't sound like a valid date/time to me... Even if the regex matching did work that way... — twalberg
– twalberg, Commented Dec 2, 2013 at 12:29

devnull · Accepted Answer · 2013-12-02 10:34:47Z

2

You could say:

if ! date -d "$datetime" >/dev/null 2>&1; then
  echo "Not a date"
fi

Using regexp isn't really recommended, but if you insist you could say:

if [[ "$datetime" != 2[0-1][0-9][0-9]-[0-1][0-9]-[0-3][0-9]\ [0-2][0-9]:[0-6][0-9]:[0-6][0-9] ]]; then
  then
    echo "Not a date"
fi

edited Dec 2, 2013 at 10:34

answered Dec 2, 2013 at 10:28

devnull

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8 Comments

devnull Over a year ago

@Steve Yes, better to use date rather than using regexp to parse date.

Steve Over a year ago

You know, this is crazy clever, because you can put it anything like "2 weeks friday 10pm" and it understands it.

devnull Over a year ago

@Steve Yup, it'll essentially validate everything that's considered good by date.

Steve Over a year ago

Yeah tried that, says it's more complex than they can easily list on the man page.

devnull Over a year ago

@MikeD I guess it wasn't obvious -- the objective of posting the regex version was an attempt to demonstrate the problem with the way OP was trying to use the regex.

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