man/cat1p/printf.1p.txt
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printf(P) printf(P)
NAME printf - write formatted output SYNOPSIS printf format[argument...] DESCRIPTION The printf utility shall write formatted operands to the standard output. The argument operands shall be format- ted under control of the format operand. OPTIONS None. OPERANDS 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. STDIN Not used. INPUT FILES None. ENVIRONMENT VARIABLES The following environment variables shall affect the execution of printf: LANG Provide a default value for the internationaliza- tion 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 cate- gories.) 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 mes- sages 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 . ASYNCHRONOUS EVENTS Default. STDOUT See the EXTENDED DESCRIPTION section. STDERR The standard error shall be used only for diagnostic messages. OUTPUT FILES None. EXTENDED DESCRIPTION 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: 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. A '' character in the format string shall be treated as a '' character, not as a <space>. 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 num- ber. The implementation shall not precede or follow output from the d or u conversion specifiers with <blank>s not specified by the format operand. The implementation shall not precede output from the o conversion specifier with zeros not specified by the format operand. The e , E , f , g , and G conversion specifiers need not be supported. 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 sup- ported: The escape sequences listed in the Base Defini- tions 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 preci- sion is omitted, it shall be taken to be infinite, so all bytes up to the end of the converted string shall be written. For each conversion specification that consumes an argu- ment, the next argument operand shall be evaluated and converted to the appropriate type for the conversion as specified below. The format operand shall be reused as often as necessary to satisfy the argument operands. Any extra c or s con- version 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 con- version 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 conver- sion 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 accumu- lated 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. EXIT STATUS The following exit values shall be returned: 0 Successful completion. >0 An error occurred. CONSEQUENCES OF ERRORS Default. The following sections are informative. APPLICATION USAGE The floating-point formatting conversion specifications of printf() are not required because all arithmetic in the shell is integer arithmetic. The awk utility per- forms floating-point calculations and provides its own printf function. The bc utility can perform arbitrary- precision floating-point arithmetic, but does not pro- vide 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() func- tion defined in the System Interfaces volume of IEEE Std 1003.1-2001 on which it is based, makes no spe- cial 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 specifi- cation. Applications should be extremely cautious using either of these features when there are multi-byte char- acters in the character set. No provision is made in this volume of IEEE Std 1003.1-2001 which allows field widths and pre- cisions 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 charac- ter. In the ISO C standard, the "##" concatenation oper- ator 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 con- stant. 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 corre- sponding conversion specification, the printf utility is required to report an error. Thus, overflow and extrane- ous characters at the end of an argument being used for a numeric conversion shall be reported as errors. 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 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 sup- plied by printf to satisfy the last %4d conversion spec- ification. 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 stan- dard output is what would be expected as the return value from the strtol() function as defined in the Sys- tem 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 charac- ter as described in the System Interfaces volume of IEEE Std 1003.1-2001. RATIONALE The printf utility was added to provide functionality that has historically been provided by echo. However, due to irreconcilable differences in the various ver- sions of echo extant, the version has few special fea- tures, 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. FUTURE DIRECTIONS None. SEE ALSO awk , bc , echo , the System Interfaces volume of IEEE Std 1003.1-2001, printf() COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operat- ing System Interface (POSIX), The Open Group Base Speci- fications Issue 6, Copyright (C) 2001-2003 by the Insti- tute 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.open- group.org/unix/online.html . POSIX 2003 printf(P) |