Hi,

Ruby substitutes the elements in the array for the percent signs in

the string. The “3d” and “04.2f” tell Ruby how to format those

numbers:

“The number is: %.2f” % 1.23456

=> “The number is: 1.23”

## The documentation for sprintf has more info:

[email protected]:~/lightconsole$ ri sprintf

--------------------------------------------------------- Kernel#sprintf

format(format_string [, arguments…] ) => string

sprintf(format_string [, arguments…] ) => string

```
Returns the string resulting from applying format_string to any
additional arguments. Within the format string, any characters
other than format sequences are copied to the result. A format
sequence consists of a percent sign, followed by optional flags,
width, and precision indicators, then terminated with a field type
character. The field type controls how the corresponding sprintf
argument is to be interpreted, while the flags modify that
interpretation. The field type characters are listed in the table
at the end of this section. The flag characters are:
Flag | Applies to | Meaning
---------+--------------+-----------------------------------------
space | bdeEfgGiouxX | Leave a space at the start of
| | positive numbers.
---------+--------------+-----------------------------------------
(digit)$ | all | Specifies the absolute argument number
| | for this field. Absolute and relative
| | argument numbers cannot be mixed in a
| | sprintf string.
---------+--------------+-----------------------------------------
# | beEfgGoxX | Use an alternative format. For the
| | conversions `o', `x', `X', and `b',
| | prefix the result with ``0'', ``0x'',
```

`0X'', | | and`

0b’’, respectively. For `e', | |`

E’, `f',`

g’, and ‘G’, force a decimal

| | point to be added, even if no digits

follow.

| | For `g’ and ‘G’, do not remove trailing

zeros.

---------±-------------±----------------------------------------

+ | bdeEfgGiouxX | Add a leading plus sign to positive

numbers.

---------±-------------±----------------------------------------

- | all | Left-justify the result of this

conversion.

---------±-------------±----------------------------------------

0 (zero) | bdeEfgGiouxX | Pad with zeros, not spaces.

---------±-------------±----------------------------------------

* | all | Use the next argument as the field

width.

| | If negative, left-justify the result.

If the

| | asterisk is followed by a number and a

dollar

| | sign, use the indicated argument as the

width.

```
The field width is an optional integer, followed optionally by a
period and a precision. The width specifies the minimum number of
characters that will be written to the result for this field. For
numeric fields, the precision controls the number of decimal
places displayed. For string fields, the precision determines the
maximum number of characters to be copied from the string. (Thus,
the format sequence %10.10s will always contribute exactly ten
characters to the result.)
The field types are:
Field | Conversion
------+--------------------------------------------------------------
b | Convert argument as a binary number.
c | Argument is the numeric code for a single character.
d | Convert argument as a decimal number.
E | Equivalent to `e', but uses an uppercase E to indicate
| the exponent.
e | Convert floating point argument into exponential
```

notation

| with one digit before the decimal point. The precision

| determines the number of fractional digits (defaulting

to six).

f | Convert floating point argument as [-]ddd.ddd,

| where the precision determines the number of digits

after

| the decimal point.

G | Equivalent to `g', but use an uppercase`

E’ in exponent

form.

g | Convert a floating point number using exponential form

| if the exponent is less than -4 or greater than or

| equal to the precision, or in d.dddd form otherwise.

i | Identical to `d’.

o | Convert argument as an octal number.

p | The valuing of argument.inspect.

s | Argument is a string to be substituted. If the format

| sequence contains a precision, at most that many

characters

| will be copied.

u | Treat argument as an unsigned decimal number. Negative

integers

| are displayed as a 32 bit two’s complement plus one for

the

| underlying architecture; that is, 2 ** 32 + n.

However, since

| Ruby has no inherent limit on bits used to represent

the

| integer, this value is preceded by two dots (…) in

order to

| indicate a infinite number of leading sign bits.

X | Convert argument as a hexadecimal number using

uppercase

| letters. Negative numbers will be displayed with two

| leading periods (representing an infinite string of

| leading 'FF’s.

x | Convert argument as a hexadecimal number.

| Negative numbers will be displayed with two

| leading periods (representing an infinite string of

| leading 'ff’s.

```
Examples:
sprintf("%d %04x", 123, 123) #=> "123 007b"
sprintf("%08b '%4s'", 123, 123) #=> "01111011 ' 123'"
sprintf("%1$*2$s %2$d %1$s", "hello", 8) #=> " hello 8
```

hello"

sprintf("%1$*2$s %2$d", “hello”, -8) #=> “hello -8”

sprintf("%+g:% g:%-g", 1.23, 1.23, 1.23) #=> “+1.23:

1.23:1.23”

sprintf("%u", -123) #=> “…4294967173”

Dan

On Wed, Apr 16, 2008 at 9:38 PM, Clement Ow