Format-Control Letters

A format specifier starts with the character `%' and ends with a format-control letter; it tells the printf statement how to output one item. (If you actually want to output a `%', write `%%'.) The format-control letter specifies what kind of value to print. The rest of the format specifier is made up of optional modifiers which are parameters to use, such as the field width.

Here is a list of the format-control letters:

c

This prints a number as an ASCII character. Thus, `printf "%c", 65' outputs the letter `A'. The output for a string value is the first character of the string.

d

i

These are equivalent. They both print a decimal integer. The `%i' specification is for compatibility with ANSI C.

e

E

This prints a number in scientific (exponential) notation. For example,

printf "%4.3e\n", 1950

prints `1.950e+03', with a total of four significant figures of which three follow the decimal point. The `4.3' are modifiers, discussed below. `%E' uses `E' instead of `e' in the output.

f

This prints a number in floating point notation. For example,

printf "%4.3f", 1950

prints `1950.000', with a total of four significant figures of which three follow the decimal point. The `4.3' are modifiers, discussed below.

g

G

This prints a number in either scientific notation or floating point notation, whichever uses fewer characters. If the result is printed in scientific notation, `%G' uses `E' instead of `e'.

o

This prints an unsigned octal integer. (In octal, or base-eight notation, the digits run from `0' to `7'; the decimal number eight is represented as `10' in octal.)

s

This prints a string.

x

X

This prints an unsigned hexadecimal integer. (In hexadecimal, or base-16 notation, the digits are `0' through `9' and `a' through `f'. The hexadecimal digit `f' represents the decimal number 15.) `%X' uses the letters `A' through `F' instead of `a' through `f'.

%

This isn't really a format-control letter, but it does have a meaning when used after a `%': the sequence `%%' outputs one `%'. It does not consume an argument, and it ignores any modifiers.

When using the integer format-control letters for values that are outside the range of a C long integer, gawk will switch to the `%g' format specifier. Other versions of awk may print invalid values, or do something else entirely (d.c.).

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