Originální popis anglicky:
printf - write formatted output
Návod, kniha: POSIX Programmer's Manual
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
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for 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 IEEE Std 1003.1-2001, 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 IEEE Std 1003.1-2001, 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>s 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 e , E , 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 IEEE Std 1003.1-2001, 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.
The
argument operands shall be treated as strings if the corresponding
conversion specifier is
b ,
c , or
s ; otherwise, it
shall be evaluated as a C constant, as described by the ISO C standard,
with the following extensions:
- *
- A leading plus 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.
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 or if a string operand's first or second
character is used to get the numeric value of a character.
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 IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001 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 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:
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
IEEE Std 1003.1-2001. 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 IEEE Std 1003.1-2001.
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
IEEE Std 1003.1-2001, Chapter 5, File Format Notation.
None.
awk ,
bc ,
echo , the System Interfaces volume of
IEEE Std 1003.1-2001,
printf()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html
.
