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PRINTF(1) BSD General Commands Manual PRINTF(1)
NAME
printf -- formatted output
SYNOPSIS
printf format [arguments ...]
DESCRIPTION
The printf utility 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 char-
acters, 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
c, b or s; otherwise it is evaluated as a C constant, with the following extensions:
o A leading plus or minus sign is allowed.
o 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 for-
mat specifications are evaluated with zero or the null string.
Character escape sequences are in backslash notation as defined in the ANSI X3.159-1989
(``ANSI C89''), with extensions. The characters and their meanings are as follows:
\a Write a <bell> character.
\b Write a <backspace> character.
\c Ignore remaining characters in this string.
\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 backslash character.
\num
\0num Write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal
number num.
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 ``alter-
nate form''. For c, d, and s, formats, this option has no effect. For the
o formats the precision of the number is increased to force the first char-
acter 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, for-
mats, the result will always contain a decimal point, even if no digits fol-
low 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 indi-
cated 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; 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 diouxXfwEgGcsb).
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 e '[-d.ddd+-dd]' where there is one digit
before the decimal point and the number after is equal to the precision specifi-
cation 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 preci-
sion in minimum space.
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; however if the precision is 0 or missing, all characters in the string
are printed.
b As for s, but interpret character escapes in backslash notation in the string
argument.
% Print a `%'; no argument is used.
The decimal point character is defined in the program's locale (category LC_NUMERIC).
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.
DIAGNOSTICS
The printf utility exits 0 on success, and >0 if an error occurs.
COMPATIBILITY
The traditional BSD behavior of converting arguments of numeric formats not beginning with a
digit to the ASCII code of the first character is not supported.
SEE ALSO
echo(1), printf(3)
STANDARDS
The printf command is expected to be compatible with the IEEE Std 1003.2 (``POSIX.2'') spec-
ification.
HISTORY
The printf command appeared in 4.3BSD-Reno. It is modeled after the standard library func-
tion, printf(3).
BUGS
Since the floating point numbers are translated from ASCII to floating-point and then back
again, floating-point precision may be lost.
ANSI hexadecimal character constants were deliberately not provided.
The escape sequence \000 is the string terminator. When present in the format, the format
will be truncated at the \000 character.
BSD June 6, 1993 BSD |
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