printf - Write formatted output

Format

printf format [argument ...]

Description

printf writes the argument operands to standard output, formatted according to the format operand.

format is a format string that is composed of conversion specifications that convert and add the next argument to the output. format can contain backslash-escape sequences. These conversions are similar to those used by the American National Standard C standard. Conversion specifications have the form: 
%[flag][width]
[precision][char]
where flag is one of the following options:
-
Left-justifies the field; default is right justification.
+
Always prefixes a signed value with a sign (+ or -).
space
Reserves a character position at the start of the string for the minus sign (for negative numbers) or a space (for positive numbers). If both space and - appear as flags, the space flag is ignored.
#
Prefixes octal values with 0 and hexadecimal values with 0x or 0X. For floating-point values, this causes the decimal point always to be displayed even if no characters follow it.
0
Pads numeric values with leading zeros. If both 0 and - appear as flags, the 0 flag is ignored.

width is the minimum field width of the output field. If the converted value is shorter than the minimum width, printf pads it with spaces or zeros.

In a string, precision is the maximum number of bytes to be printed from the string; in a number, the precision is the number of digits to be printed to right of the decimal point in a floating-point value. width or precision can be specified as *, in which case the value is read from the next argument, which must be an integer. For example: 
printf "%*.*d\n" 20 10 200
is equivalent to: 
printf "%20.10d\n" 200
The conversion character char is one of the following:
b
A string that may contain a backslash-escape sequence.
c
Single character of an integer value; the first character of a string.
d
Decimal integer.
e,E
Floating point (scientific notation).
f,F
Floating point.
g,G
The shorter of e and f (suppresses nonsignificant zeros).
i
Decimal integer.
o
Unsigned octal integer.
s
String.
u
Unsigned decimal integer.
x,X
Unsigned hexadecimal integer.

When there are more arguments than positions in format, the format string is applied again to the remaining arguments. When there are fewer arguments than there are positions in the format string, printf fills the remaining positions with null strings (character fields) or zeros (numeric fields).

Caution

The POSIX.2POSIX.2 printf facility (like the C language printf on which it is based), does not accommodate double-byte characters gracefully when using %c conversion, or either of %b or %s conversions with a specified precision. Use these features cautiously when you have double-byte characters in the character set.

In a double-byte environment, normal backslash-escape characters are handled correctly (printf shifts state as required) but octal and hexadecimal escape characters do not change state. This behavior is significant in a shift-lock environment. For example, if an octal escape character contains the shift-in character, it is the user's responsibility to ensure that there is also a shift-out character. Further, an octal or hexadecimal backslash escape character that comes immediately after a double-byte character may or may not be processed in the shifted state.

Localization

printf uses the following localization environment variables:
  • LANG
  • LC_ALL
  • LC_CTYPE
  • LC_MESSAGES
  • LC_NUMERIC
  • LC_SYNTAX
  • NLSPATH

Exit values

0
Successful completion.
>0
The number of failures due to any of the following reasons:
  • Missing format specifications.
  • Arguments that were supplied for a format string that does not accept them (that is, that has no %s).
  • Incorrect integer argument.
  • Incorrect floating-point argument.

Portability

POSIX.2, X/Open Portability Guide, UNIX System V.

The %F format and the handling of * as a width or precision argument are extensions of the POSIX standard.

Related information

echo, printf