PRINTF(1)

PRINTF(1) | General Commands Manual | PRINTF(1)

# NAME

printf — formatted output

# SYNOPSIS

printf | format [arguments ...]

# DESCRIPTION

printf formats and prints its arguments, after the first, under control of the format. The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument.

The arguments after the first are treated as strings if the corresponding format is either b, B, c, or s; otherwise it is evaluated as a C constant, with the following extensions:

- A leading plus or minus sign is allowed.
- If the leading character is a single or double quote, the value is the ASCII code of the next character.

The format string is reused as often as necessary to satisfy the arguments. Any extra format specifications are evaluated with zero or the null string.

Character escape sequences are in backslash notation as defined in ANSI X3.159-1989 (“ANSI C89”). The characters and their meanings are as follows:

\e
  Write an <escape> character.
\a
  Write a <bell> character.
\b
  Write a <backspace> character.
\f
  Write a <form-feed> character.
\n
  Write a <new-line> character.
\r
  Write a <carriage return> character.
\t
  Write a <tab> character.
\v
  Write a <vertical tab> character.
\́
  Write a <single quote> character.
\"
  Write a <double quote> character.
\\
  Write a backslash character.
\num
  Write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal number num.
\xxx
  Write an 8-bit character whose ASCII value is the 1- or 2-digit hexadecimal number xx.

Each format specification is introduced by the percent character (“%”). The remainder of the format specification includes, in the following order:

Zero or more of the following flags:
  #
    A ‘#’ character specifying that the value should be printed in an “alternative form”. For b, c, d, and s formats, this option has no effect. For the o format the precision of the number is increased to force the first character of the output string to a zero. For the x (X) format, a non-zero result has the string `0x` (`0X`) prepended to it. For e, E, f, g, and G formats, the result will always contain a decimal point, even if no digits follow the point (normally, a decimal point only appears in the results of those formats if a digit follows the decimal point). For g and G formats, trailing zeros are not removed from the result as they would otherwise be.
  -
    A minus sign ‘-’ which specifies left adjustment of the output in the indicated field;
  +
    A ‘+’ character specifying that there should always be a sign placed before the number when using signed formats.
  ‘ ’
    A space specifying that a blank should be left before a positive number for a signed format. A ‘+’ overrides a space if both are used;
  0
    A zero `0' character indicating that zero-padding should be used rather than blank-padding. A ‘-’ overrides a ‘0’ if both are used;
Field Width:
  An optional digit string specifying a field width; if the output string has fewer characters than the field width it will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width (note that a leading zero is a flag, but an embedded zero is part of a field width);
Precision:
  An optional period, ‘.’, followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, for e and f formats, or the maximum number of characters to be printed from a string (b, B, and s formats); if the digit string is missing, the precision is treated as zero;
Format:
  A character which indicates the type of format to use (one of diouxXfwEgGbBcs).

A field width or precision may be ‘*’ instead of a digit string. In this case an argument supplies the field width or precision.

The format characters and their meanings are:

diouXx
  The argument is printed as a signed decimal (d or i), unsigned octal, unsigned decimal, or unsigned hexadecimal (X or x), respectively.
f
  The argument is printed in the style [-]ddd.ddd where the number of d's after the decimal point is equal to the precision specification for the argument. If the precision is missing, 6 digits are given; if the precision is explicitly 0, no digits and no decimal point are printed.
eE
  The argument is printed in the style [-]d.ddde±dd where there is one digit before the decimal point and the number after is equal to the precision specification for the argument; when the precision is missing, 6 digits are produced. An upper-case E is used for an ‘E’ format.
gG
  The argument is printed in style f or in style e (E) whichever gives full precision in minimum space.
b
  Characters from the string argument are printed with backslash-escape sequences expanded.

  The following additional backslash-escape sequences are supported:

  \c
    Causes printf to ignore any remaining characters in the string operand containing it, any remaining string operands, and any additional characters in the format operand.
  \0num
    Write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal number num.
  \^c
    Write the control character c. Generates characters `\000' through `\037`, and `\177' (from `\^?').
  \M-c
    Write the character c with the 8th bit set. Generates characters `\241' through `\376`.
  \M^c
    Write the control character c with the 8th bit set. Generates characters `\200' through `\237`, and `\377' (from `\M^?').
B
  Characters from the string argument are printed with unprintable characters backslash-escaped using the `\c',`\^c',`\M-c'or`\M^c', formats described above.
c
  The first character of argument is printed.
s
  Characters from the string argument are printed until the end is reached or until the number of characters indicated by the precision specification is reached; if the precision is omitted, all characters in the string are printed.
%
  Print a `%'; no argument is used.

In no case does a non-existent or small field width cause truncation of a field; padding takes place only if the specified field width exceeds the actual width.

# EXIT STATUS

The printf utility exits 0 on success, and >0 if an error occurs.

# SEE ALSO

echo(1), printf(3), vis(3), printf(9)

# STANDARDS

The printf utility conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

Support for the floating point formats and `*' as a field width and precision are optional in POSIX.

The behaviour of the %B format and the \', \", \xxx, \e and \[M][-|^]c escape sequences are undefined in POSIX.

# BUGS

Since the floating point numbers are translated from ASCII to floating-point and then back again, floating-point precision may be lost.

Hexadecimal character constants are restricted to, and should be specified as, two character constants. This is contrary to the ISO C standard but does guarantee detection of the end of the constant.

# NOTES

All formats which treat the argument as a number first convert the argument from its external representation as a character string to an internal numeric representation, and then apply the format to the internal numeric representation, producing another external character string representation. One might expect the %c format to do likewise, but in fact it does not.

To convert a string representation of a decimal, octal, or hexadecimal number into the corresponding character, two nested printf invocations may be used, in which the inner invocation converts the input to an octal string, and the outer invocation uses the octal string as part of a format. For example, the following command outputs the character whose code is 0x0A, which is a newline in ASCII:

> `printf "$(printf "\\%o" "0x0A")"`

May 6, 2008 | NetBSD 7.0