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man pages section 1: User Commands

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Updated: Thursday, June 13, 2019
 
 

printf(1)

Name

printf - write formatted output

Synopsis

/usr/bin/printf

printf format [argument]...

ksh

printf format [string...]

Description

/usr/bin/printf

The printf utility writes each string operand to standard output using format to control the output format.

Operands

/usr/bin/printf

The following operands are supported by /usr/bin/printf:

format

A string describing the format to use to write the remaining operands. The format operand is used as the format string described on the formats(7) manual page, with the following exceptions:

  • A SPACE character in the format string, in any context other than a flag of a conversion specification, is treated as an ordinary character that is copied to the output.

  • A character in the format string is treated as a character, not as a SPACE character.

  • In addition to the escape sequences described on the formats(7) manual page (\\, \a, \b , \f, \n, \r, \t, \v), \ddd, where ddd is a one-, two- or three-digit octal number, is written as a byte with the numeric value specified by the octal number.

  • The program does not precede or follow output from the d or u conversion specifications with blank characters not specified by the format operand.

  • The program does not precede output from the o conversion specification with zeros not specified by the format operand.

  • An additional conversion character, b, is supported as follows. The argument is taken to be a string that can contain backslash-escape sequences. The following backslash-escape sequences are supported:

    • the escape sequences listed on the formats(7) manual page (\\, \a, \b, \f, \n, \r, \t, \v), which are converted to the characters they represent

    • \0ddd, where ddd is a zero-, one-, two- or three-digit octal number that is converted to a byte with the numeric value specified by the octal number

    • \c, which is written and 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.

The interpretation of a backslash followed by any other sequence of characters is unspecified.

Bytes from the converted string are 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 is taken to be infinite, so all bytes up to the end of the converted string are written. For each specification that consumes an argument, the next argument operand is evaluated and converted to the appropriate type for the conversion as specified below. The format operand is reused as often as necessary to satisfy the argument operands. 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. If the format operand contains no conversion specifications and argument operands are present, the results are unspecified. If a character sequence in the format operand begins with a % character, but does not form a valid conversion specification, the behavior is unspecified.

argument

The strings to be written to standard output, under the control of format. The argument operands are treated as strings if the corresponding conversion character is b, c or s. Otherwise, it is evaluated as a C constant, as described by the ISO C standard, 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 numeric value in the underlying codeset of the character following the single- or double-quote.

If an argument operand cannot be completely converted into an internal value appropriate to the corresponding conversion specification, a diagnostic message is written to standard error and the utility does not exit with a zero exit status, but continues processing any remaining operands and writes the value accumulated at the time the error was detected to standard output.

ksh

The format operands support the full range of ANSI C/C99/XPG6 formatting specifiers as well as additional specifiers:

%b

Each character in the string operand is processed specially, as follows:

\a

Alert character.

\b

Backspace character.

\c

Terminate output without appending NEWLINE. The remaining string operands are ignored.

\E

Escape character (ASCII octal 033).

\f

FORM FEED character.

\n

NEWLINE character.

\t

TAB character.

\v

Vertical tab character.

\\

Backslash character.

\0x

The 8-bit character whose ASCII code is the 1-, 2-, or 3-digit octal number x.

%B

Treat the argument as a variable name and output the value without converting it to a string. This is most useful for variables of type –b.

%H

Output string with characters <, &, >, ", and non-printable characters, properly escaped for use in HTML and XML documents.

%P

Treat string as an extended regular expression and convert it to a shell pattern.

%q

Output string quoted in a manner that it can be read in by the shell to get back the same string. However, empty strings resulting from missing string operands are not quoted.

%R

Treat string as an shell pattern expression and convert it to an extended regular expression.

%T

Treat string as a date/time string and format it. The T can be preceded by (dformat), where dformat is a date format as defined by the date(1) command.

%Z

Output a byte whose value is 0.

When performing conversions of string to satisfy a numeric format specifier, if the first character of string is "or', the value is the numeric value in the underlying code set of the character following the "or'. Otherwise, string is treated like a shell arithmetic expression and evaluated.

If a string operand cannot be completely converted into a value appropriate for that format specifier, an error occurs, but remaining string operands continue to be processed.

In addition to the format specifier extensions, the following extensions of ANSI C/C99/XPG6 are permitted in format specifiers:

  • The escape sequences \E and \e expand to the escape character which is octal 033 in ASCII.

  • The escape sequence \cx expands to CTRL-x.

  • The escape sequence \C[.name.] expands to the collating element name.

  • The escape sequence \x{hex}expands to the character corresponding to the hexadecimal value hex.

  • The format modifier flag = can be used to center a field to a specified width. When the output is a terminal, the character width is used rather than the number of bytes.

  • Each of the integral format specifiers can have a third modifier after width and precision that specifies the base of the conversion from 2 to 64. In this case, the # modifier causes base# to be prepended to the value.

  • The # modifier can be used with the d specifier when no base is specified to cause the output to be written in units of 1000 with a suffix of one of k M G T P E.

  • The # modifier can be used with the i specifier to cause the output to be written in units of 1024 with a suffix of one of Ki Mi Gi Ti Pi Ei.

If there are more string operands than format specifiers, the format string is reprocessed from the beginning. If there are fewer string operands than format specifiers, then string specifiers are treated as if empty strings were supplied, numeric conversions are treated as if 0 was supplied, and time conversions are treated as if now was supplied.

/usr/bin/printf is equivalent to ksh's printf built-in and print -f, which allows additional options to be specified.

Usage

/usr/bin/printf

The printf utility, like the printf(3C) function on which it is based, makes no special provision for dealing with multi-byte characters when using the %c conversion specification. Applications should be extremely cautious using either of these features when there are multi-byte characters in the character set.

Field widths and precisions cannot be specified as *.

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 USAGE section of the echo(1) manual page 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 reports an error. Thus, overflow and extraneous characters at the end of an argument being used for a numeric conversion are to be reported as errors.

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.

Examples

/usr/bin/printf Examples

Example 1 Printing a Series of Prompts

The following example alerts the user, then prints and reads a series of prompts:

example% printf "\aPlease fill in the following: \nName: "
read name
printf "Phone number: "
read phone
Example 2 Printing a Table of Calculations

The following example prints a table of calculations. It reads out a list of right and wrong answers from a file, calculates the percentage correctly, and prints them out. The numbers are right-justified and separated by a single tab character. The percentage is written to one decimal place of accuracy:

example% 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
Example 3 Printing number strings

The command:

example% printf "%5d%4d\n" 1 21 321 4321 54321

produces:

    1  21
  3214321
54321   0

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.

Example 4 Tabulating Conversion Errors

The following example tabulates conversion errors.

The printf utility tells the user when conversion errors are detected while producing numeric output. These results would be expected on an implementation with 32-bit twos-complement integers when %d is specified as the format operand:

Arguments
Standard
Diagnostic
5a
5
printf: 5a not completely converted
9999999999
2147483647
printf: 9999999999: Results too large
-9999999999
-2147483648
printf: -9999999999: Results too large
ABC
0
printf: ABC expected numeric value

The value shown on standard output is what would be expected as the return value from the function strtol(3C). A similar correspondence exists between %u and strtoul(3C), and %e, %f and %g and strtod(3C).

Example 5 Printing Output for a Specific Locale

The following example prints output for a specific locale. In a locale using the ISO/IEC 646:1991 standard as the underlying codeset, the command:

example% 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 SO/IEC 646:1991 standard codeset

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.

If an argument operand cannot be completely converted into an internal value appropriate to the corresponding conversion specification, a diagnostic message is written to standard error and the utility does exit with a zero exit status, but continues processing any remaining operands and writes the value accumulated at the time the error was detected to standard output.

ksh Examples

The following examples illustrate the use of the ksh93 version of printf.

Example 6 Alternative floating point representation 1

The printf utility supports an alternative floating point representation (see printf(3C) entry for the “%a”/” %A”), which allows the output of floating-point values in a format that avoids the usual base16 to base10 rounding errors.

example% printf "%a\n" 2 3.1 NaN

produces:

0x1.0000000000000000000000000000p+01
0x1.8ccccccccccccccccccccccccccdp+01
nan
Example 7 Alternative floating point representation 2

The following example shows two different representations of the same floating-point value.

example% x=2 ; printf "%f == %a\n" x x

produces:

2.000000 == 0x1.0000000000000000000000000000p+01
Example 8 Output of unicode values

The following command will print the EURO unicode symbol (code-point 0x20ac).

example% LC_ALL=en_US.UTF-8 printf "\u[20ac]\n"

produces:

<euro>

where <euro> represents the EURO currency symbol character.

Example 9 Convert unicode character to unicode code-point value

The following command will print the hexadecimal value of a given character.

example% export LC_ALL=en_US.UTF-8
example% printf "%x\n" "'<euro>"

where <euro> represents the EURO currency symbol character (code-point 0x20ac).

produces:

20ac
Example 10 Print the numeric value of an ASCII character
example% printf "%d\n" "'A"

produces:

65
Example 11 Print the language-independent date and time format

To print the language-independent date and time format, the following statement could be used:

example% printf "format" weekday month day hour min

For example,

$ printf format "Sunday" "July" 3 10 2

For American usage, format could be the string:

"%s, %s %d, %d:%.2d\n"

producing the message:

Sunday, July 3, 10:02

Whereas for EU usage, format could be the string:

"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"

Note that the '$' characters must be properly escaped, such as

"%1\$s, %3\$d. %2\$s, %4\$d:%5\$.2d\n" in this case

producing the message:

Sunday, 3. July, 10:02

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of printf: LANG, LC_ALL , LC_CTYPE, LC_MESSAGES, LC_NUMERIC, and NLSPATH.

Exit Status

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

Attributes

See attributes(7) for descriptions of the following attributes:

/usr/bin/printf

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
text/locale
CSI
Enabled
Interface Stability
Committed
Standard

ksh

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os
Interface Stability
Uncommitted

See Also

awk(1), bc(1), date(1), echo(1), ksh(1), printf(3C), strtod(3C), strtol(3C), strtoul(3C), attributes(7), environ(7), formats(7), standards(7)

Notes

Using format specifiers (characters following '%') which are not listed in the printf(3C) or this manual page will result in undefined behavior.

Using escape sequences (the character following a backslash ('\')) which are not listed in the printf(3C) or this manual page will result in undefined behavior.

Floating-point values follow C99, XPG6 and IEEE 754 standard behavior and can handle values the same way as the platform's |long double| datatype.

Floating-point values handle the sign separately which allows signs for values like NaN (for example, -nan), Infinite (for example, -inf) and zero (for example, -0.0).