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gawk: Printf Ordering

 
 13.4.2 Rearranging 'printf' Arguments
 -------------------------------------
 
 Format strings for 'printf' and 'sprintf()' (Printf) present a
 special problem for translation.  Consider the following:(1)
 
      printf(_"String `%s' has %d characters\n",
                string, length(string)))
 
    A possible German translation for this might be:
 
      "%d Zeichen lang ist die Zeichenkette `%s'\n"
 
    The problem should be obvious: the order of the format specifications
 is different from the original!  Even though 'gettext()' can return the
 translated string at runtime, it cannot change the argument order in the
 call to 'printf'.
 
    To solve this problem, 'printf' format specifiers may have an
 additional optional element, which we call a "positional specifier".
 For example:
 
      "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n"
 
    Here, the positional specifier consists of an integer count, which
 indicates which argument to use, and a '$'.  Counts are one-based, and
 the format string itself is _not_ included.  Thus, in the following
 example, 'string' is the first argument and 'length(string)' is the
 second:
 
      $ gawk 'BEGIN {
      >     string = "Don\47t Panic"
      >     printf "%2$d characters live in \"%1$s\"\n",
      >                         string, length(string)
      > }'
      -| 11 characters live in "Don't Panic"
 
    If present, positional specifiers come first in the format
 specification, before the flags, the field width, and/or the precision.
 
    Positional specifiers can be used with the dynamic field width and
 precision capability:
 
      $ gawk 'BEGIN {
      >    printf("%*.*s\n", 10, 20, "hello")
      >    printf("%3$*2$.*1$s\n", 20, 10, "hello")
      > }'
      -|      hello
      -|      hello
 
      NOTE: When using '*' with a positional specifier, the '*' comes
      first, then the integer position, and then the '$'.  This is
      somewhat counterintuitive.
 
    'gawk' does not allow you to mix regular format specifiers and those
 with positional specifiers in the same string:
 
      $ gawk 'BEGIN { printf "%d %3$s\n", 1, 2, "hi" }'
      error-> gawk: cmd. line:1: fatal: must use `count$' on all formats or none
 
      NOTE: There are some pathological cases that 'gawk' may fail to
      diagnose.  In such cases, the output may not be what you expect.
      It's still a bad idea to try mixing them, even if 'gawk' doesn't
      detect it.
 
    Although positional specifiers can be used directly in 'awk'
 programs, their primary purpose is to help in producing correct
 translations of format strings into languages different from the one in
 which the program is first written.
 
    ---------- Footnotes ----------
 
    (1) This example is borrowed from the GNU 'gettext' manual.
 

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