bin/145748: hexdump(1) %s format qualifier broken

Garrett Cooper yanegomi at
Wed Apr 21 00:50:03 UTC 2010

The following reply was made to PR bin/145748; it has been noted by GNATS.

From: Garrett Cooper <yanegomi at>
To: Wayne Sierke <ws at>
Cc: bug-followup at
Subject: Re: bin/145748: hexdump(1) %s format qualifier broken
Date: Tue, 20 Apr 2010 17:49:43 -0700

 On Tue, Apr 20, 2010 at 7:33 AM, Wayne Sierke <ws at> wrote:
 >> The fact that "%4s" fails and isn't noted in the addendum is a failure
 >> according to the specifications of hexdump as per the manpage; "%.4s"
 >> passing is a reasonable workaround for broken "%[:digit:]s"
 >> functionality.
 > I should have made my earlier reply more explicit. It doesn't seem to be
 > a failure.
 The issue with %4s failing is still a failure. The non-issue with
 %.4s, %0.4s etc not failing is not a failure; it's just a bit more
 obfuscated logic.
 > The part of the hexdump(1) manpage quoted previously:
 > o A byte count or field precision is required for each ``s'' con-
 > version character (unlike the fprintf(3) default which prints
 > the entire string if the precision is unspecified).
 That statement is misleading. It should make the above statement with
 field width, not [field] precision. FWIW, the statement `field
 precision' makes absolutely no sense in the terminology used by
 printf(3), and is most likely a typo.
 And finally, yes I agree that %s is illegal because you can't qualify
 the number of characters required for each format unit -- something
 that's required for hexdump to function. %4s, etc with precision not
 being specified is legal however.
 > And as observed hexdump does accept the required value when passed a
 > "field precision" - the numeric value immediately after the period in
 > "%.4s" (NB not a "field width" - as described in fprintf(3) and slightly
 > more clearly in printf(3)).
 From printf(3):
      o   An optional decimal digit string specifying a minimum field width.
          If the converted value has fewer characters than the field width, it
          will be padded with spaces on the left (or right, if the left-adjust-
          ment flag has been given) to fill out the field width.
      o   An optional precision, in the form of a period . followed by an
          optional digit string.  If the digit string is omitted, the precision
          is taken as zero.  This gives the minimum number of digits to appear
          for d, i, o, u, x, and X conversions, the number of digits to appear
          after the decimal-point for a, A, e, E, f, and F conversions, the
          maximum number of significant digits for g and G conversions, or the
          maximum number of characters to be printed from a string for s con-
 Note the word `optional' in the first and second clauses. `.' isn't
 required except to disambiguate precision from field width.

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