date pipe - bug or my mistake?

sy flag

I faced a strange behavior of the date command:

echo '1 JAN 2023' | LC_ALL=en_US.utf8  date -d -

This produces plainly wrong output:

Sun Jun 11 12:00:00 AM CEST 2023

But this is ok:

LC_ALL=en_US.utf8  date -d '1 Jan 2023'  # Sun Jan  1 12:00:00 AM CET 2023

This is ok as well:

my_date='1 JAN 2023'
LC_ALL=en_US.utf8  date -d  "$my_date" # Sun Jan  1 12:00:00 AM CET 2023

I cannot get the pipe version working. Is a bug or am I doing something wrong?

hr flag

The date command's --date / -d option expects a string argument - the standard input is discarded, and - is parsed as a date input string according to the GNU date command's General date syntax, which says

Hyphens not followed by a digit are currently ignored.


The empty string means the beginning of today (i.e., midnight).

So your command is simply equivalent to LC_ALL=en_US.utf8 date -d 'today 00:00'.

To take input from a pipe, you'd either need to convert stdin to an argument - for example with xargs:

$ echo '1 JAN 2023' | LC_ALL=en_US.utf8  xargs -d '\n' date -d
Sun Jan  1 12:00:00 AM EST 2023

or (as suggested by Raffa) by passing it through to a command that does read standard input, capturing that command's output in a command substitution:

$ echo '1 JAN 2023' | LC_ALL=en_US.utf8  date -d "$(cat -)"
Sun Jan  1 12:00:00 AM EST 2023

It's much simpler to use the -f option instead, which does read from standard input:

$ echo '1 JAN 2023' | LC_ALL=en_US.utf8  date -f -
Sun Jan  1 12:00:00 AM EST 2023

From man date:

   -f, --file=DATEFILE
          like --date; once for each line of DATEFILE
Raffa avatar
jp flag
Might be worth noting that utilities that can read and *echo* from the pipe such as `cat` and `tee` should work as well in a command substitution syntax ... e.g. `echo '1 JAN 2023' | date -d "$(cat)"` and `echo '1 JAN 2023' | date -d "$(tee)"`
hr flag
@Raffa thanks - done
xerostomus avatar
sy flag
Thank you all, I guess that "date -f - " is the best as it is no bashism, this is as it ought to work. (Stdin is a virtual file in fact.) It is nice to have so many smart people around, isn't it? :-)
cn flag

As others mentioned, date doesn't read from standard input; the -d option expects the date string in the next argument. You can use command substitution to put the output of a command there.

date -d "$(echo '1 JAN 2023')"
ua flag

I don't know what version of date are you using but man date doesn't mention that when - is specified input is taken from standard input:

$ echo something | date -d -
Sun Jun 11 00:00:00 CEST 2023
$ date -d -
Sun Jun 11 00:00:00 CEST 2023
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