STANDARD INPUT

None.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of printf:

LANG

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

LC_ALL

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

LC_CTYPE

This variable shall determine the locale for the interpretation of sequences of bytes of text data as characters (e.g., single- versus multibyte characters in arguments).

LC_MESSAGES

This variable shall determine the language in which messages should be written.

LC_NUMERIC

This variable shall determine the locale for numeric formatting. It shall affect the format of numbers written using the e, E, f, g, and G conversion characters (if supported).

ASYNCHRONOUS EVENTS

Default.

STANDARD OUTPUT

See EXTENDED DESCRIPTION .

STANDARD ERROR

Used only for diagnostic messages.

OUTPUT FILES

None.

EXAMPLES

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 right, 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 Diagnostic Output 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 C Standard {7} function strtol(). 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 ISO / IEC 646 {1} as the underlying code set, 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 ISO / IEC 646 {1} code set 43 Numeric value of the character ‘‘+’’ in ISO / IEC 646 {1} code set 45 Numeric value of the character ‘‘−’’ in ISO / IEC 646 {1} code set

Note that in a locale with multibyte 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 C Standard {7}.

HISTORY OF DECISIONS MADE

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 in this standard has few special features, leaving those to this new printf utility, which is based on one in the Ninth Edition at AT&T Bell Labs.

The Extended Description almost exactly matches the C Standard {7} printf function, although it is described in terms of the file format notation in 2.12. The floating point formatting conversion specifications 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 doesn’t 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 C Standard {7} printf function on which it is based, makes no special provision for dealing with multibyte 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 multibyte characters in the character set. Field widths and precisions cannot 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 C Standard {7} 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 nonhex-digit character. In the C Standard {7}, 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 C Standard {7}; it has been added here as a portable way to process backslash-escapes expanded in string operands as provided by the System V version of the echo utility. See also the rationale for 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 are to be reported as errors. If written in C, the printf utility could use the strtol() function to parse optionally signed numeric arguments, strtoul() to parse unsigned numeric arguments, and strtod() to parse floating point arguments (if floating point conversions are supported). 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.