Re: strftime() using '-' to remove leading 0s functionality removed or broken?

[arnold]

Here is what I plan to add to the manual.

diff --git a/doc/gawk.texi b/doc/gawk.texi
index 1b758db3..e4da785f 100644
--- a/doc/gawk.texi
+++ b/doc/gawk.texi
@@ -19949,6 +19949,14 @@ The date in OpenVMS format (e.g., @samp{20-JUN-1991}).
 Additionally, the alternative representations are recognized but their
 normal representations are used.
 
+@quotation NOTE
+Similar to @code{printf()}, some versions of @code{strftime()} support
+the use of flags between the @code{%} and the format specification
+letter.  Check your local manpage for @code{strftime()} to see if it
+supports flags or not, and what they are. Be aware, however, that using
+any such flags is likely to make your script less portable to other systems.
+@end quotation
+
 @cindex @code{date} utility @subentry POSIX
 @cindex POSIX @command{awk} @subentry @code{date} utility and
 The following example is an @command{awk} implementation of the POSIX


Ed Morton <mortoneccc@comcast.net> wrote:

> Arnold - Yeah I don’t blame you. You could spend your life trying to
> keep up with things outside of your control and there’s definitely a
> strong argument for “if you’re using something that’s not documented
> then you’re on your own”. Thanks for taking a look.
>
> Ed Morton
>
> > On Jan 27, 2024, at 1:06 PM, arnold@skeeve.com wrote:
> > 
> > Hi Ed.
> > 
> > It's definitely an issue with the underlying C library version of
> > strftime, which is what gawk uses.
> > 
> > I'll take a look at the manual, but I'm not sure I want to
> > get into details like '-' flags which are unportable.
> > 
> > Thanks,
> > 
> > Arnold
> > 
> > Ed Morton <mortoneccc@comcast.net> wrote:
> > 
> >> Apparently the person for whom the `-` works in gawk 4.2.1 also sees it 
> >> working in gawk 5.3.0, see:
> >> 
> >>    https://imgur.com/a/YtgCkA6
> >> 
> >> They are testing on a Mac while I tested on 2 different laptops, both 
> >> running Windows 11, one in cygwin and the other git bash, so I'm 
> >> guessing this is something to do with underlying primitives. It's odd to 
> >> me  that `date` behaves differently from `gawk` in this regard but I 
> >> guess it's just implemented differently. FWIW perl behaves the same way 
> >> as gawk:
> >> 
> >>    $ cat tst.prl
> >>    #!/usr/bin/perl
> >>    use POSIX qw(strftime);
> >> 
> >>    # Modules used
> >>    use strict;
> >>    use warnings;
> >> 
> >>    # Print function
> >>    printf("Without -: %s\n", strftime "%m", localtime);
> >>    printf("With -:%s\n", strftime "%-m", localtime);
> >> 
> >>    $ ./tst.prl
> >>    Without -: 01
> >>    With -:
> >>    $
> >> 
> >> and so does python:
> >> 
> >>    $ cat tst.py
> >>    #!/usr/bin/python
> >>    from datetime import datetime
> >> 
> >>    now = datetime.now()
> >> 
> >>    print("Without -:", now.strftime("%m"))
> >>    print("With -:", now.strftime("%-m"))
> >> 
> >>    $ ./tst.py
> >>    Without -: 01
> >>    With -:
> >> 
> >> Assuming it's not something that can/should be made to work portably, 
> >> maybe it's worth a brief note in the documentation that this is a thing, 
> >> just like the underlying primitives impact on rounding and reading 
> >> binary files are described elsewhere in the docs?
> >> 
> >>     Ed.
> >> 
> >>> On 1/27/2024 6:56 AM, Ed Morton wrote:
> >>> Someone posted an answer at 
> >>> https://stackoverflow.com/a/77884684/1745001 that puts a `-` in front 
> >>> of `strftime()` format specifiers to remove leading `0`s so that, for 
> >>> example, we can print the month number by doing:
> >>> 
> >>>    awk 'BEGIN{print strftime("%-m")}'
> >>> 
> >>> and get `1` output instead of the `01` we'd get with
> >>> 
> >>>    awk 'BEGIN{print strftime("%m")}'
> >>> 
> >>> That's consistent with how GNU date (and apparently various other 
> >>> tools) works:
> >>> 
> >>>    $ date +'%-m'
> >>>    1
> >>>    $
> >>> 
> >>>    $ date +'%m'
> >>>    01
> >>>    $
> >>> 
> >>> and it's what that SO answer shows with gawk 4.2.1.
> >>> 
> >>> When I try to do the same with gawk 5.0.0 or later, though, then I get:
> >>> 
> >>>    $ awk 'BEGIN{print strftime("%-m")}'
> >>> 
> >>>    $
> >>> 
> >>>    $ awk 'BEGIN{print strftime("%m")}'
> >>>    01
> >>>    $
> >>> 
> >>> i.e. adding the `-` makes `strftime()` produce no output.
> >>> 
> >>> That functionality isn't documented in the manual best I can tell - is 
> >>> that functionality that was removed or is it breakage or something else?
> >>> 
> >>>     Ed.
>