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printf(1)
NAME
printf - Writes formatted output
SYNOPSIS
printf format [argument...]
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
printf: XCU5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
None
OPERANDS
format
A string describing the manner of writing the output. This string is
explained in the DESCRIPTION section.
argument
The strings to be written under the control of the format. These
strings are explained in the DESCRIPTION section.
DESCRIPTION
The printf command converts, formats, and writes its arguments to the
standard output. The values specified by the argument variable are
formatted under control of the format variable.
Syntax of the argument Variable
The argument variable is a list of one or more strings to be written to the
standard output under the control of the format variable. These are
treated as strings if the corresponding conversion character is b, c, or s;
otherwise, it is evaluated as a C constant, with the following extensions:
A leading + (plus sign) or - (minus sign) is allowed.
If the leading character is a ' (single quote) or " (double quote), the
value is the numeric value in the underlying code set of the character
following the single quote or double quote.
Syntax of the format Variable
The format variable is a character string that contains three types of
objects:
· Plain characters that are copied to the output stream.
· The following escape sequences are both copied to the output stream
and cause the associated action to occur on display devices that are
capable of the action.
\\ Backslash
\a Alert
\b Backspace
\f Formfeed
\n Newline
\r Carriage Return
\t Tab
\v Vertical Tab
\ddd
Where ddd is a one-, two-, or three-digit octal number. These
escape sequences are displayed as a byte with the numeric value
specified by the octal number.
· A delta character in the format string is treated as a delta
character, rather than as a space character.
The format variable is reused as often as necessary to satisfy the
arguments. Any extra c or s conversion specifications are evaluated as if a
null string argument were supplied; other extra conversion specifications
are evaluated as if a zero argument were supplied.
Each conversion specification in the format variable has the following
syntax:
1. A % (percent sign).
2. Zero or more options, which modify the meaning of the conversion
specification. The option characters and their meanings are as
follows:
- The result of the conversion is left aligned within the field.
+ The result of a signed conversion always begins with a + (plus) or
- (minus).
blank
If the first character of a signed conversion is not a sign, a
blank is prefixed to the result. If both the blank and + options
appear, then the blank option is ignored.
# The value is converted to an alternative form. For c, d, i, u,
and s conversions, the option has no effect. For o conversion, it
increases the precision to force the first digit of the result to
be a 0 (zero). For x and X conversions, a nonzero result has 0x,
or 0X prefixed to it, respectively. For e, E, f, g, and G
conversions, the result always contains a radix character, even if
no digits follow the radix character. For g and G conversions,
trailing zeros are not removed from the result as they usually
are.
0 For d, i, o, u, x, X, e, E, f, g, and G conversions, leading zeros
(following any indication of sign or base) are used to pad to the
field width, no space padding is performed. If the 0 (zero) and -
options appear, the 0 (zero) option is ignored. For d, i, o, u, x,
and X conversions, if a precision is specified, the 0 (zero)
option is ignored.
3. An optional decimal digit string that specifies the minimum field
width. If the converted value has fewer characters than the field
width, the field is padded on the left to the length specified by the
field width. If the left-adjustment option flag (-) is specified, the
field is padded on the right.
4. An optional precision. The precision is a . (dot) followed by an
asterisk (*), or a decimal digit string. If no precision is given, it
is treated as 0 (zero). The precision specifies:
· The minimum number of digits to appear for the d, o, i, u, x, or
X conversions.
· The number of digits to appear after the radix character for the
e and f conversions.
· The maximum number of significant digits for the g conversion.
· The maximum number of bytes to be printed from a string in the s
conversion.
5. A character that indicates the type of conversion to be applied, as
follows:
% Performs no conversion. Prints a % (percent sign).
b Accepts a value as a string that may contain backslash-escape
sequences. Bytes from the converted string are printed until the
end of the string or number of bytes indicated by the precision
specification is reached. If the precision is omitted, all bytes
until the first null character are printed.
The following backslash-escape sequences are supported:
· The \Oddd sequence, where ddd is a one-, two-, or three-digit
octal number that is converted to a byte with the numeric
value specified by the octal number.
· The escape sequences previously listed under the description
of the format variable. These are converted to the individual
characters they represented.
· The \c sequence, which is not displayed and causes the printf
command to ignore any remaining characters in the string
parameter containing it, any remaining string parameters, and
any additional characters in the format variable.
c Prints the first character of the argument.
d, i
Accepts an integer value and converts it to a signed decimal
notation in the style [-]dddd. The precision specifies the
minimum number of digits to appear. If the value being converted
can be represented in fewer digits, it is expanded with leading
zeros. The default precision is 1. The result of converting a 0
(zero) value with a precision of 0 (zero) is a null string.
Specifying a field width with a 0 (zero) as a leading character
causes the field to be padded with leading zeros.
e, E
Accepts a float or double value and converts it to the exponential
form [-] d.dde +|- dd. There is one digit before the radix
character (shown here as the decimal point), and the number of
digits after the radix character is equal to the precision
specification. The LC_NUMERIC locale category determines the radix
character to use in this format. If no precision is specified,
then six digits are output. If the precision is 0 (zero), then no
radix character appears. The E conversion character produces a
number with E instead of e before the exponent. The exponent
always contains at least two digits. However, if the value to be
printed requires an exponent greater than two digits, additional
exponent digits are printed as necessary.
f Accepts a float or double value and converts it to decimal
notation in the format [-] ddd.ddd. The number of digits after
the radix character (shown here as the decimal point) is equal to
the precision specification. The LC_NUMERIC locale category
determines the radix character to use in this format. If no
precision is specified, then six digits are output. If the
precision is 0 (zero), then no radix character appears.
g, G
Accepts a float or double value and converts it in the style of
the f or e conversion characters (or E in the case of the G
conversion), with the precision specifying the number of
significant digits. Trailing zeros are removed from the result. A
radix character appears only if it is followed by a digit. The
style used depends on the value converted. Style g results only if
the exponent resulting from the conversion is less than -4, or if
it is greater than or equal to the precision.
o Accepts an integer value and converts it to unsigned octal
notation. The precision specifies the minimum number of digits to
appear. If the value being converted can be represented in fewer
digits, it is expanded with leading zeros. The default precision
is 1. The result of converting a 0 (zero) value with a precision
of 0 (zero) is a null string. Specifying a field width with a 0
(zero) as a leading character causes the field width value to be
padded with leading zeros. An octal value for field width is not
implied.
s Accepts a value as a string, and bytes from the string are printed
until the end of the string is encountered or the number of bytes
indicated by the precision is reached. If no precision is
specified, all characters up to the first null character are
printed.
u Accepts an integer value and converts it to unsigned decimal
notation. The precision specifies the minimum number of digits to
appear. If the value being converted can be represented in fewer
digits, it is expanded with leading zeros. The default precision
is 1. The result of converting a 0 (zero) value with a precision
of 0 (zero) is a null string. Specifying a field width with a 0
(zero) as a leading character causes the field width value to be
padded with leading zeros.
x, X
Accepts an integer value and converts it to unsigned hexadecimal
notation. The letters abcdef are used for the x conversion and the
letters ABCDEF are used for the X conversion. The precision
specifies the minimum number of digits to appear. If the value
being converted can be represented in fewer digits, it is expanded
with leading zeros. The default precision is 1. The result of
converting a 0 (zero) value with a precision of 0 (zero) is a null
string. Specifying a field width with a 0 (zero) as a leading
character causes the field width value to be padded with leading
zeros.
If the result of a conversion is wider than the field width, the field is
expanded to contain the converted result. No truncation occurs. However, a
small precision may cause truncation on the right.
EXAMPLES
1. The following printf command formats a series of numbers:
printf "%5d%4d\n" 1 21 321 4321 54321
This command produces the following output:
1 21
3214321
54321 0
The format variable is used three times to print all of the given
strings. The 0 (zero) is supplied by the printf command to satisfy the
last %4d conversion specification.
2. The following script includes printf commands to alert the user (sound
a beep) and to display prompts for entering a name and phone number.
The script then appends the user entries to a file.
printf "\aPlease fill in the following: \nName: "
read name
printf "Phone number: "
read phone
echo $name " " $phone >> phone_list
echo >> phone_list
ENVIRONMENT VARIABLES
The following environment variables affect the execution of printf:
LANG
Provides a default value for the internationalization variables that
are unset or null. If LANG is unset or null, the corresponding value
from the default locale is used. If any of the internationalization
variables contain an invalid setting, the utility behaves as if none of
the variables had been defined.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
Determines the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multibyte characters in arguments).
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
Determines the location of message catalogues for the processing of
LC_MESSAGES.
LC_NUMERIC
Determines the locale for numbers written using the e, E, f, g, or G
conversion characters.
SEE ALSO
Commands: awk(1), bc(1), echo(1), read(1)
Functions: printf(3)
Standards: standards(5)
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