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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
PRINTF(1P) POSIX Programmer's Manual PRINTF(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
printf — write formatted output
printf format [argument...]
The printf utility shall write formatted operands to the standard
output. The argument operands shall be formatted under control of the
format operand.
None.
The following operands shall be supported:
format A string describing the format to use to write the
remaining operands. See the EXTENDED DESCRIPTION section.
argument The strings to be written to standard output, under the
control of format. See the EXTENDED DESCRIPTION section.
Not used.
None.
The following environment variables shall affect the execution of
printf:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte
as opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
LC_NUMERIC
Determine the locale for numeric formatting. It shall
affect the format of numbers written using the e, E, f, g,
and G conversion specifier characters (if supported).
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
See the EXTENDED DESCRIPTION section.
The standard error shall be used only for diagnostic messages.
None.
The format operand shall be used as the format string described in
the Base Definitions volume of POSIX.1‐2008, Chapter 5, File Format
Notation with the following exceptions:
1. A <space> in the format string, in any context other than a flag
of a conversion specification, shall be treated as an ordinary
character that is copied to the output.
2. A '' character in the format string shall be treated as a ''
character, not as a <space>.
3. In addition to the escape sequences shown in the Base Definitions
volume of POSIX.1‐2008, Chapter 5, File Format Notation ('\\',
'\a', '\b', '\f', '\n', '\r', '\t', '\v'), "\ddd", where ddd is a
one, two, or three-digit octal number, shall be written as a byte
with the numeric value specified by the octal number.
4. The implementation shall not precede or follow output from the d
or u conversion specifiers with <blank> characters not specified
by the format operand.
5. The implementation shall not precede output from the o conversion
specifier with zeros not specified by the format operand.
6. The a, A, e, E, f, F, g, and G conversion specifiers need not be
supported.
7. An additional conversion specifier character, b, shall be
supported as follows. The argument shall be taken to be a string
that may contain <backslash>-escape sequences. The following
<backslash>-escape sequences shall be supported:
-- The escape sequences listed in the Base Definitions volume of
POSIX.1‐2008, Chapter 5, File Format Notation ('\\', '\a',
'\b', '\f', '\n', '\r', '\t', '\v'), which shall be converted
to the characters they represent
-- "\0ddd", where ddd is a zero, one, two, or three-digit octal
number that shall be converted to a byte with the numeric
value specified by the octal number
-- '\c', which shall not be written and shall cause printf to
ignore any remaining characters in the string operand
containing it, any remaining string operands, and any
additional characters in the format operand
The interpretation of a <backslash> followed by any other
sequence of characters is unspecified.
Bytes from the converted string shall be written until the end of
the string or the number of bytes indicated by the precision
specification is reached. If the precision is omitted, it shall
be taken to be infinite, so all bytes up to the end of the
converted string shall be written.
8. For each conversion specification that consumes an argument, the
next argument operand shall be evaluated and converted to the
appropriate type for the conversion as specified below.
9. The format operand shall be reused as often as necessary to
satisfy the argument operands. Any extra c or s conversion
specifiers shall be evaluated as if a null string argument were
supplied; other extra conversion specifications shall be
evaluated as if a zero argument were supplied. If the format
operand contains no conversion specifications and argument
operands are present, the results are unspecified.
10. If a character sequence in the format operand begins with a '%'
character, but does not form a valid conversion specification,
the behavior is unspecified.
11. The argument to the c conversion specifier can be a string
containing zero or more bytes. If it contains one or more bytes,
the first byte shall be written and any additional bytes shall be
ignored. If the argument is an empty string, it is unspecified
whether nothing is written or a null byte is written.
The argument operands shall be treated as strings if the
corresponding conversion specifier is b, c, or s, and shall be
evaluated as if by the strtod() function if the corresponding
conversion specifier is a, A, e, E, f, F, g, or G. Otherwise, they
shall be evaluated as unsuffixed C integer constants, as described by
the ISO C standard, with the following extensions:
* A leading <plus-sign> or minus-sign shall be allowed.
* If the leading character is a single-quote or double-quote, the
value shall be the numeric value in the underlying codeset of the
character following the single-quote or double-quote.
* Suffixed integer constants may be allowed.
If an argument operand cannot be completely converted into an
internal value appropriate to the corresponding conversion
specification, a diagnostic message shall be written to standard
error and the utility shall not exit with a zero exit status, but
shall continue processing any remaining operands and shall write the
value accumulated at the time the error was detected to standard
output.
It is not considered an error if an argument operand is not
completely used for a c or s conversion.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
The floating-point formatting conversion specifications of printf()
are not required because all arithmetic in the shell is integer
arithmetic. The awk utility performs floating-point calculations and
provides its own printf function. The bc utility can perform
arbitrary-precision floating-point arithmetic, but does not provide
extensive formatting capabilities. (This printf utility cannot really
be used to format bc output; it does not support arbitrary
precision.) Implementations are encouraged to support the floating-
point conversions as an extension.
Note that this printf utility, like the printf() function defined in
the System Interfaces volume of POSIX.1‐2008 on which it is based,
makes no special provision for dealing with multi-byte characters
when using the %c conversion specification or when a precision is
specified in a %b or %s conversion specification. Applications should
be extremely cautious using either of these features when there are
multi-byte characters in the character set.
No provision is made in this volume of POSIX.1‐2008 which allows
field widths and precisions to be specified as '*' since the '*' can
be replaced directly in the format operand using shell variable
substitution. Implementations can also provide this feature as an
extension if they so choose.
Hexadecimal character constants as defined in the ISO C standard are
not recognized in the format operand because there is no consistent
way to detect the end of the constant. Octal character constants are
limited to, at most, three octal digits, but hexadecimal character
constants are only terminated by a non-hex-digit character. In the
ISO C standard, the "##" concatenation operator can be used to
terminate a constant and follow it with a hexadecimal character to be
written. In the shell, concatenation occurs before the printf utility
has a chance to parse the end of the hexadecimal constant.
The %b conversion specification is not part of the ISO C standard; it
has been added here as a portable way to process <backslash>-escapes
expanded in string operands as provided by the echo utility. See also
the APPLICATION USAGE section of echo(1p) for ways to use printf as a
replacement for all of the traditional versions of the echo utility.
If an argument cannot be parsed correctly for the corresponding
conversion specification, the printf utility is required to report an
error. Thus, overflow and extraneous characters at the end of an
argument being used for a numeric conversion shall be reported as
errors.
To alert the user and then print and read a series of prompts:
printf "\aPlease fill in the following: \nName: "
read name
printf "Phone number: "
read phone
To read out a list of right and wrong answers from a file, calculate
the percentage correctly, and print them out. The numbers are right-
justified and separated by a single <tab>. The percentage is written
to one decimal place of accuracy:
while read right wrong ; do
percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
printf "%2d right\t%2d wrong\t(%s%%)\n" \
$right $wrong $percent
done < database_file
The command:
printf "%5d%4d\n" 1 21 321 4321 54321
produces:
1 21
3214321
54321 0
Note that the format operand is used three times to print all of the
given strings and that a '0' was supplied by printf to satisfy the
last %4d conversion specification.
The printf utility is required to notify the user when conversion
errors are detected while producing numeric output; thus, the
following results would be expected on an implementation with 32-bit
twos-complement integers when %d is specified as the format operand:
┌────────────┬─────────────┬───────────────────────────────────────────┐
│ │ Standard │ │
│ Argument │ Output │ Diagnostic Output │
├────────────┼─────────────┼───────────────────────────────────────────┤
│5a │ 5 │ printf: "5a" not completely converted │
│9999999999 │ 2147483647 │ printf: "9999999999" arithmetic overflow │
│−9999999999 │ −2147483648 │ printf: "−9999999999" arithmetic overflow │
│ABC │ 0 │ printf: "ABC" expected numeric value │
└────────────┴─────────────┴───────────────────────────────────────────┘
The diagnostic message format is not specified, but these examples
convey the type of information that should be reported. Note that the
value shown on standard output is what would be expected as the
return value from the strtol() function as defined in the System
Interfaces volume of POSIX.1‐2008. A similar correspondence exists
between %u and strtoul() and %e, %f, and %g (if the implementation
supports floating-point conversions) and strtod().
In a locale using the ISO/IEC 646:1991 standard as the underlying
codeset, the command:
printf "%d\n" 3 +3 −3 \'3 \"+3 "'−3"
produces:
3 Numeric value of constant 3
3 Numeric value of constant 3
−3 Numeric value of constant −3
51 Numeric value of the character '3' in the ISO/IEC 646:1991
standard codeset
43 Numeric value of the character '+' in the ISO/IEC 646:1991
standard codeset
45 Numeric value of the character '−' in the ISO/IEC 646:1991
standard codeset
Note that in a locale with multi-byte characters, the value of a
character is intended to be the value of the equivalent of the
wchar_t representation of the character as described in the System
Interfaces volume of POSIX.1‐2008.
The printf utility was added to provide functionality that has
historically been provided by echo. However, due to irreconcilable
differences in the various versions of echo extant, the version has
few special features, leaving those to this new printf utility, which
is based on one in the Ninth Edition system.
The EXTENDED DESCRIPTION section almost exactly matches the printf()
function in the ISO C standard, although it is described in terms of
the file format notation in the Base Definitions volume of
POSIX.1‐2008, Chapter 5, File Format Notation.
Earlier versions of this standard specified that arguments for all
conversions other than b, c, and s were evaluated in the same way (as
C constants, but with stated exceptions). For implementations
supporting the floating-point conversions it was not clear whether
integer conversions need only accept integer constants and floating-
point conversions need only accept floating-point constants, or
whether both types of conversions should accept both types of
constants. Also by not distinguishing between them, the requirement
relating to a leading single-quote or double-quote applied to
floating-point conversions even though this provided no useful
functionality to applications that was not already available through
the integer conversions. The current standard clarifies the situation
by specifying that the arguments for floating-point conversions are
evaluated as if by strtod(), and the arguments for integer
conversions are evaluated as C integer constants, with the special
treatment of leading single-quote and double-quote applying only to
integer conversions.
None.
awk(1p), bc(1p), echo(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 5, File Format
Notation, Chapter 8, Environment Variables
The System Interfaces volume of POSIX.1‐2008, fprintf(3p), strtod(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PRINTF(1P)
Pages that refer to this page: echo(1p), file(1p), pax(1p)