Why is one of these date commands valid and the other not?

Question

[user@mymachine folder]$ echo `date --date=tomorrow +%Y%m%d`
20160802
[user@mymachine folder]$ echo `date -d=tomorrow +%Y%m%d`
date: invalid date `=tomorrow'

I'm using Centos 5 if that makes any difference.

Short options are separated from their argument by a space: date --date=tomorrow +%Y%m%d date -d tomorrow +%Y%m%d — user4556274, Aug 01 '16 at 18:52
Thank you. Most helpful. I can see that you are correct on my machine. — seanmus, Aug 01 '16 at 18:54
@user4556274: Post that as an answer as it is obviously valid. — Julie Pelletier, Aug 01 '16 at 19:01
(1) Why are you saying echo \date --date=tomorrow +%Y%m%d`` instead of just date --date=tomorrow +%Y%m%d?   (2) If you have a reason to use command substitution, you might want to change \…`` to $(…) just for clarity — see this, this, and this. — G-Man Says 'Reinstate Monica', Aug 03 '16 at 22:11

sjsam · Accepted Answer · 2016-08-01T19:14:02.827

3

The short options or unix style options are usually separated from its argument using a space, but space is not strictly required in some cases

For instance

echo `date -dtomorrow +%Y%m%d`

and

echo `date -d tomorrow +%Y%m%d`

would work just fine

However in case of,

echo date -d=tomorrow +%Y%m%d

=tomorrow is considered the argument to d but it doesn't make a valid date string

edited Aug 01 '16 at 19:14

answered Aug 01 '16 at 19:02

sjsam

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Why is one of these date commands valid and the other not?

1 Answers1