Re: date does not support pipes

[Marc Chantreux]

On Sat, Jan 13, 2024 at 11:08:52AM +0100, Philip Rogers wrote:
> Thanks for the reply.

you're welcome.

> 1. Other utils do not require `-` to be specified, do they? For example, the
> manpage for sed says:
> > if no input files are specified, then the standard input is read.

because sed is a filter so it is expected to consume a stream which is
stdin by default.

On the other hand, date is a "generator" with no need to read from
stdin for its default behavior.

-f is the way to transform date into a generator
-  means "the relavant stdio", stdin in this case.

> 2. In any case, I think it should be documented to pass `-` to read from
> stdin

from date (1)             - print or set the system date and time

       -f, --file=DATEFILE
              like --date; once for each line of DATEFILE

the - thing is a convention in unix. should it be documented in all the
filter man pages?

> 3. The command `stat --format "%Y" check.txt | date -f-` does not work. It
> returns:
> 
> > date: invalid date ‘1705140089’


oh … you're right.  maybe it's worth a patch? btw this work:

        stat --format "%y" /etc/hostname | date -f-

> 4. On a related note, the man page I think should also document the use of
> `@` for seconds since the epoch.

this is in the examples section.

> Thanks again and best regards,

coreutils team will probably argue that it is documented in the section 29.9
of the info documentation.

        info date --index-search=Epoch

regards
marc