printf: move help strings to markdown file

[m11o]

issue: #4368

printf --help outputs the following.

./target/debug/printf --help
Print output based off of the format string and proceeding arguments.

Usage: ../../../target/debug/printf FORMATSTRING [ARGUMENT]...

Arguments:
  [FORMATSTRING]  
  [ARGUMENT]...   

Options:
      --help     Print help information
      --version  Print version information

basic anonymous string templating:

prints format string at least once, repeating as long as there are remaining arguments
output prints escaped literals in the format string as character literals
output replaces anonymous fields with the next unused argument, formatted according to the field.

Prints the , replacing escaped character sequences with character literals
and substitution field sequences with passed arguments

literally, with the exception of the below
escaped character sequences, and the substitution sequences described further down.

### ESCAPE SEQUENCES

The following escape sequences, organized here in alphabetical order,
will print the corresponding character literal:

* \"      double quote

* \\\\    backslash

* \\a     alert (BEL)

* \\b     backspace

* \\c     End-of-Input

* \\e     escape

* \\f     form feed

* \\n     new line

* \\r     carriage return

* \\t     horizontal tab

* \\v     vertical tab

* \\NNN   byte with value expressed in octal value NNN (1 to 3 digits)
          values greater than 256 will be treated

* \\xHH   byte with value expressed in hexadecimal value NN (1 to 2 digits)

* \\uHHHH Unicode (IEC 10646) character with value expressed in hexadecimal value HHHH (4 digits)

* \\uHHHH Unicode character with value expressed in hexadecimal value HHHH (8 digits)

* %%      a single %

### SUBSTITUTIONS

#### SUBSTITUTION QUICK REFERENCE

Fields

* %s: string
* %b: string parsed for literals second parameter is max length

* %c: char no second parameter

* %i or %d: 64-bit integer
* %u:       64 bit unsigned integer
* %x or %X: 64-bit unsigned integer as hex
* %o:       64-bit unsigned integer as octal
            second parameter is min-width, integer
            output below that width is padded with leading zeroes

* %f or %F: decimal floating point value
* %e or %E: scientific notation floating point value
* %g or %G: shorter of specially interpreted decimal or SciNote floating point value.
            second parameter is
              -max places after decimal point for floating point output
              -max number of significant digits for scientific notation output

parameterizing fields

examples:


printf '%4.3i' 7


It has a first parameter of 4 and a second parameter of 3 and will result in ' 007'


printf '%.1s' abcde


It has no first parameter and a second parameter of 1 and will result in 'a'


printf '%4c' q


It has a first parameter of 4 and no second parameter and will result in  '   q'

The first parameter of a field is the minimum width to pad the output to
if the output is less than this absolute value of this width,
it will be padded with leading spaces, or, if the argument is negative,
with trailing spaces. the default is zero.

The second parameter of a field is particular to the output field type.
defaults can be found in the full substitution help below

special prefixes to numeric arguments

* 0 (e.g. 010):    interpret argument as octal (integer output fields only)
* 0x (e.g. 0xABC): interpret argument as hex (numeric output fields only)
* \' (e.g. \'a):   interpret argument as a character constant

#### HOW TO USE SUBSTITUTIONS

Substitutions are used to pass additional argument(s) into the FORMAT string, to be formatted a
particular way. E.g.


printf 'the letter %X comes before the letter %X' 10 11


will print
'the letter A comes before the letter B'

because the substitution field %X means
'take an integer argument and write it as a hexadecimal number'

Passing more arguments than are in the format string will cause the format string to be
repeated for the remaining substitutions


printf 'it is %i F in %s \n' 22 Portland 25 Boston 27 New York


will print
'it is 22 F in Portland
it is 25 F in Boston
it is 27 F in Boston
'
If a format string is printed but there are less arguments remaining
than there are substitution fields, substitution fields without
an argument will default to empty strings, or for numeric fields
the value 0

#### AVAILABLE SUBSTITUTIONS

This program, like GNU coreutils printf,
interprets a modified subset of the POSIX C printf spec,
a quick reference to substitutions is below.

#### STRING SUBSTITUTIONS

All string fields have a 'max width' parameter
%.3s means 'print no more than three characters of the original input'

* %s: string

* %b: escaped string - the string will be checked for any escaped literals from
      the escaped literal list above, and translate them to literal characters.
      e.g. \\n will be transformed into a newline character.
      One special rule about %b mode is that octal literals are interpreted differently
      In arguments passed by %b, pass octal-interpreted literals must be in the form of \\0NNN
      instead of \\NNN. (Although, for legacy reasons, octal literals in the form of \\NNN will
      still be interpreted and not throw a warning, you will have problems if you use this for a
      literal whose code begins with zero, as it will be viewed as in \\0NNN form.)

#### CHAR SUBSTITUTIONS

The character field does not have a secondary parameter.

* %c: a single character

#### INTEGER SUBSTITUTIONS

All integer fields have a 'pad with zero' parameter
%.4i means an integer which if it is less than 4 digits in length,
is padded with leading zeros until it is 4 digits in length.

* %d or %i: 64-bit integer

* %u: 64-bit unsigned integer

* %x or %X: 64-bit unsigned integer printed in Hexadecimal (base 16)
            %X instead of %x means to use uppercase letters for 'a' through 'f'

* %o: 64-bit unsigned integer printed in octal (base 8)

#### FLOATING POINT SUBSTITUTIONS

All floating point fields have a 'max decimal places / max significant digits' parameter
%.10f means a decimal floating point with 7 decimal places past 0
%.10e means a scientific notation number with 10 significant digits
%.10g means the same behavior for decimal and Sci. Note, respectively, and provides the shortest
of each's output.

Like with GNU coreutils, the value after the decimal point is these outputs is parsed as a
double first before being rendered to text. For both implementations do not expect meaningful
precision past the 18th decimal place. When using a number of decimal places that is 18 or
higher, you can expect variation in output between GNU coreutils printf and this printf at the
18th decimal place of +/- 1

* %f: floating point value presented in decimal, truncated and displayed to 6 decimal places by
      default. There is not past-double behavior parity with Coreutils printf, values are not
      estimated or adjusted beyond input values.

* %e or %E: floating point value presented in scientific notation
            7 significant digits by default
            %E means use to use uppercase E for the mantissa.

* %g or %G: floating point value presented in the shortest of decimal and scientific notation
            behaves differently from %f and %E, please see posix printf spec for full details,
            some examples of different behavior:
            Sci Note has 6 significant digits by default
            Trailing zeroes are removed
            Instead of being truncated, digit after last is rounded

Like other behavior in this utility, the design choices of floating point
behavior in this utility is selected to reproduce in exact
the behavior of GNU coreutils' printf from an inputs and outputs standpoint.

### USING PARAMETERS

Most substitution fields can be parameterized using up to 2 numbers that can
be passed to the field, between the % sign and the field letter.

The 1st parameter always indicates the minimum width of output, it is useful for creating
columnar output. Any output that would be less than this minimum width is padded with
leading spaces
The 2nd parameter is proceeded by a dot.
You do not have to use parameters

### SPECIAL FORMS OF INPUT

For numeric input, the following additional forms of input are accepted besides decimal:

Octal (only with integer): if the argument begins with a 0 the proceeding characters
will be interpreted as octal (base 8) for integer fields

Hexadecimal: if the argument begins with 0x the proceeding characters will be interpreted
will be interpreted as hex (base 16) for any numeric fields
for float fields, hexadecimal input results in a precision
limit (in converting input past the decimal point) of 10^-15

Character Constant: if the argument begins with a single quote character, the first byte
of the next character will be interpreted as an 8-bit unsigned integer. If there are
additional bytes, they will throw an error (unless the environment variable POSIXLY_CORRECT
is set)

[sylvestre]

please use a list here

[sylvestre]

please remove all that

[sylvestre]

please fix the warnings

[sylvestre]

please use ``` for the example

[sylvestre]

please run rustfmt

[sylvestre]

in general, could you please use more * when it is list
` for keyword
and

```for examples

thanks

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail-2/inotify-dir-recreate. tests/tail-2/inotify-dir-recreate is passing on 'main'. Maybe you have to rebase?

[sylvestre]

Suggested change

	will print
	'it is 22 F in Portland
	it is 25 F in Boston
	it is 27 F in Boston
	'
	will print

it is 22 F in Portland
it is 25 F in Boston
it is 27 F in Boston

[sylvestre]

please replace this by ```

[sylvestre]

how does the -h usage display now?
Because the preview on github shows \\ while it should be \ (the others have the same issue)

[m11o]

@sylvestre

Thank you for your feedback.

how does the -h usage display now?

I have confirmed the output we executed printf --help

Because the preview on github shows \ while it should be \ (the others have the same issue)

I would like to clarify my intentions with the proposed changes:

1. I adhered to the existing code format, preserving the original escape sequences.
2. I used backticks (` `) to emphasize the keywords.

I have a question regarding to the points you raised.

In Markdown, to display an alert(BEL, \a) using an escape sequence, it is necessary to write it as \\a. However, we execute printf --help, it would display \\a instead of just \a.
I recognize that there is a discrepancy between the Markdown format and the actual output of the command.

I would be genuinely grateful for your guidance on which should be considered correct. Should we prioritize the Markdown format or the actual output of the printf --help command?

Thanks.