1PRINTF(1P) POSIX Programmer's Manual PRINTF(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 printf — write formatted output
14
16 printf format [argument...]
17
19 The printf utility shall write formatted operands to the standard out‐
20 put. The argument operands shall be formatted under control of the for‐
21 mat operand.
22
24 None.
25
27 The following operands shall be supported:
28 format A string describing the format to use to write the remaining
30 operands. See the EXTENDED DESCRIPTION section.
31 argument The strings to be written to standard output, under the con‐
33 trol of format. See the EXTENDED DESCRIPTION section.
34
36 Not used.
37
39 None.
40
42 The following environment variables shall affect the execution of
43 printf:
44 LANG Provide a default value for the internationalization vari‐
46 ables that are unset or null. (See the Base Definitions vol‐
47 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
48 ables the precedence of internationalization variables used
49 to determine the values of locale categories.)
50 LC_ALL If set to a non-empty string value, override the values of
52 all the other internationalization variables.
53 LC_CTYPE Determine the locale for the interpretation of sequences of
55 bytes of text data as characters (for example, single-byte as
56 opposed to multi-byte characters in arguments).
57 LC_MESSAGES
59 Determine the locale that should be used to affect the format
60 and contents of diagnostic messages written to standard
61 error.
62 LC_NUMERIC
64 Determine the locale for numeric formatting. It shall affect
65 the format of numbers written using the e, E, f, g, and G
66 conversion specifier characters (if supported).
67 NLSPATH Determine the location of message catalogs for the processing
69 of LC_MESSAGES.
70
72 Default.
73
75 See the EXTENDED DESCRIPTION section.
76
78 The standard error shall be used only for diagnostic messages.
79
81 None.
82
84 The format operand shall be used as the format string described in the
85 Base Definitions volume of POSIX.1‐2008, Chapter 5, File Format Nota‐
86 tion with the following exceptions:
87 1. A <space> in the format string, in any context other than a flag of
89 a conversion specification, shall be treated as an ordinary charac‐
90 ter that is copied to the output.
91 2. A '' character in the format string shall be treated as a '' char‐
93 acter, not as a <space>.
94 3. In addition to the escape sequences shown in the Base Definitions
96 volume of POSIX.1‐2008, Chapter 5, File Format Notation ('\\',
97 '\a', '\b', '\f', '\n', '\r', '\t', '\v'), "\ddd", where ddd is a
98 one, two, or three-digit octal number, shall be written as a byte
99 with the numeric value specified by the octal number.
100 4. The implementation shall not precede or follow output from the d or
102 u conversion specifiers with <blank> characters not specified by
103 the format operand.
104 5. The implementation shall not precede output from the o conversion
106 specifier with zeros not specified by the format operand.
107 6. The a, A, e, E, f, F, g, and G conversion specifiers need not be
109 supported.
110 7. An additional conversion specifier character, b, shall be supported
112 as follows. The argument shall be taken to be a string that may
113 contain <backslash>-escape sequences. The following <back‐
114 slash>-escape sequences shall be supported:
115 -- The escape sequences listed in the Base Definitions volume of
117 POSIX.1‐2008, Chapter 5, File Format Notation ('\\', '\a',
118 '\b', '\f', '\n', '\r', '\t', '\v'), which shall be converted
119 to the characters they represent
120 -- "\0ddd", where ddd is a zero, one, two, or three-digit octal
122 number that shall be converted to a byte with the numeric value
123 specified by the octal number
124 -- '\c', which shall not be written and shall cause printf to
126 ignore any remaining characters in the string operand contain‐
127 ing it, any remaining string operands, and any additional char‐
128 acters in the format operand
129 The interpretation of a <backslash> followed by any other sequence
131 of characters is unspecified.
132 Bytes from the converted string shall be written until the end of
134 the string or the number of bytes indicated by the precision speci‐
135 fication is reached. If the precision is omitted, it shall be taken
136 to be infinite, so all bytes up to the end of the converted string
137 shall be written.
138 8. For each conversion specification that consumes an argument, the
140 next argument operand shall be evaluated and converted to the
141 appropriate type for the conversion as specified below.
142 9. The format operand shall be reused as often as necessary to satisfy
144 the argument operands. Any extra c or s conversion specifiers shall
145 be evaluated as if a null string argument were supplied; other
146 extra conversion specifications shall be evaluated as if a zero
147 argument were supplied. If the format operand contains no conver‐
148 sion specifications and argument operands are present, the results
149 are unspecified.
150 10. If a character sequence in the format operand begins with a '%'
152 character, but does not form a valid conversion specification, the
153 behavior is unspecified.
154 11. The argument to the c conversion specifier can be a string contain‐
156 ing zero or more bytes. If it contains one or more bytes, the first
157 byte shall be written and any additional bytes shall be ignored. If
158 the argument is an empty string, it is unspecified whether nothing
159 is written or a null byte is written.
160 The argument operands shall be treated as strings if the corresponding
162 conversion specifier is b, c, or s, and shall be evaluated as if by the
163 strtod() function if the corresponding conversion specifier is a, A, e,
164 E, f, F, g, or G. Otherwise, they shall be evaluated as unsuffixed C
165 integer constants, as described by the ISO C standard, with the follow‐
166 ing extensions:
167 * A leading <plus-sign> or minus-sign shall be allowed.
169 * If the leading character is a single-quote or double-quote, the
171 value shall be the numeric value in the underlying codeset of the
172 character following the single-quote or double-quote.
173 * Suffixed integer constants may be allowed.
175 If an argument operand cannot be completely converted into an internal
177 value appropriate to the corresponding conversion specification, a
178 diagnostic message shall be written to standard error and the utility
179 shall not exit with a zero exit status, but shall continue processing
180 any remaining operands and shall write the value accumulated at the
181 time the error was detected to standard output.
182 It is not considered an error if an argument operand is not completely
184 used for a c or s conversion.
185
187 The following exit values shall be returned:
188 0 Successful completion.
190 >0 An error occurred.
192
194 Default.
195 The following sections are informative.
197
199 The floating-point formatting conversion specifications of printf() are
200 not required because all arithmetic in the shell is integer arithmetic.
201 The awk utility performs floating-point calculations and provides its
202 own printf function. The bc utility can perform arbitrary-precision
203 floating-point arithmetic, but does not provide extensive formatting
204 capabilities. (This printf utility cannot really be used to format bc
205 output; it does not support arbitrary precision.) Implementations are
206 encouraged to support the floating-point conversions as an extension.
207 Note that this printf utility, like the printf() function defined in
209 the System Interfaces volume of POSIX.1‐2008 on which it is based,
210 makes no special provision for dealing with multi-byte characters when
211 using the %c conversion specification or when a precision is specified
212 in a %b or %s conversion specification. Applications should be
213 extremely cautious using either of these features when there are multi-
214 byte characters in the character set.
215 No provision is made in this volume of POSIX.1‐2008 which allows field
217 widths and precisions to be specified as '*' since the '*' can be
218 replaced directly in the format operand using shell variable substitu‐
219 tion. Implementations can also provide this feature as an extension if
220 they so choose.
221 Hexadecimal character constants as defined in the ISO C standard are
223 not recognized in the format operand because there is no consistent way
224 to detect the end of the constant. Octal character constants are lim‐
225 ited to, at most, three octal digits, but hexadecimal character con‐
226 stants are only terminated by a non-hex-digit character. In the ISO C
227 standard, the "##" concatenation operator can be used to terminate a
228 constant and follow it with a hexadecimal character to be written. In
229 the shell, concatenation occurs before the printf utility has a chance
230 to parse the end of the hexadecimal constant.
231 The %b conversion specification is not part of the ISO C standard; it
233 has been added here as a portable way to process <backslash>-escapes
234 expanded in string operands as provided by the echo utility. See also
235 the APPLICATION USAGE section of echo for ways to use printf as a
236 replacement for all of the traditional versions of the echo utility.
237 If an argument cannot be parsed correctly for the corresponding conver‐
239 sion specification, the printf utility is required to report an error.
240 Thus, overflow and extraneous characters at the end of an argument
241 being used for a numeric conversion shall be reported as errors.
242
244 To alert the user and then print and read a series of prompts:
245 printf "\aPlease fill in the following: \nName: "
247 read name
248 printf "Phone number: "
249 read phone
250 To read out a list of right and wrong answers from a file, calculate
252 the percentage correctly, and print them out. The numbers are right-
253 justified and separated by a single <tab>. The percentage is written
254 to one decimal place of accuracy:
255 while read right wrong ; do
257 percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
258 printf "%2d right\t%2d wrong\t(%s%%)\n" \
259 $right $wrong $percent
260 done < database_file
261 The command:
263 printf "%5d%4d\n" 1 21 321 4321 54321
265 produces:
267 1 21
269 3214321
270 54321 0
271 Note that the format operand is used three times to print all of the
273 given strings and that a '0' was supplied by printf to satisfy the last
274 %4d conversion specification.
275 The printf utility is required to notify the user when conversion
277 errors are detected while producing numeric output; thus, the following
278 results would be expected on an implementation with 32-bit twos-comple‐
279 ment integers when %d is specified as the format operand:
280 ┌────────────┬─────────────┬───────────────────────────────────────────┐
282 │ │ Standard │ │
283 │ Argument │ Output │ Diagnostic Output │
284 ├────────────┼─────────────┼───────────────────────────────────────────┤
285 │5a │ 5 │ printf: "5a" not completely converted │
286 │9999999999 │ 2147483647 │ printf: "9999999999" arithmetic overflow │
287 │−9999999999 │ −2147483648 │ printf: "−9999999999" arithmetic overflow │
288 │ABC │ 0 │ printf: "ABC" expected numeric value │
289 └────────────┴─────────────┴───────────────────────────────────────────┘
290 The diagnostic message format is not specified, but these examples con‐
291 vey the type of information that should be reported. Note that the
292 value shown on standard output is what would be expected as the return
293 value from the strtol() function as defined in the System Interfaces
294 volume of POSIX.1‐2008. A similar correspondence exists between %u and
295 strtoul() and %e, %f, and %g (if the implementation supports floating-
296 point conversions) and strtod().
297 In a locale using the ISO/IEC 646:1991 standard as the underlying code‐
299 set, the command:
300 printf "%d\n" 3 +3 −3 \'3 \"+3 "'−3"
302 produces:
304 3 Numeric value of constant 3
306 3 Numeric value of constant 3
308 −3 Numeric value of constant −3
310 51 Numeric value of the character '3' in the ISO/IEC 646:1991 stan‐
312 dard codeset
313 43 Numeric value of the character '+' in the ISO/IEC 646:1991 stan‐
315 dard codeset
316 45 Numeric value of the character '−' in the ISO/IEC 646:1991 stan‐
318 dard codeset
319 Note that in a locale with multi-byte characters, the value of a char‐
321 acter is intended to be the value of the equivalent of the wchar_t rep‐
322 resentation of the character as described in the System Interfaces vol‐
323 ume of POSIX.1‐2008.
324
326 The printf utility was added to provide functionality that has histori‐
327 cally been provided by echo. However, due to irreconcilable differ‐
328 ences in the various versions of echo extant, the version has few spe‐
329 cial features, leaving those to this new printf utility, which is based
330 on one in the Ninth Edition system.
331 The EXTENDED DESCRIPTION section almost exactly matches the printf()
333 function in the ISO C standard, although it is described in terms of
334 the file format notation in the Base Definitions volume of
335 POSIX.1‐2008, Chapter 5, File Format Notation.
336 Earlier versions of this standard specified that arguments for all con‐
338 versions other than b, c, and s were evaluated in the same way (as C
339 constants, but with stated exceptions). For implementations supporting
340 the floating-point conversions it was not clear whether integer conver‐
341 sions need only accept integer constants and floating-point conversions
342 need only accept floating-point constants, or whether both types of
343 conversions should accept both types of constants. Also by not distin‐
344 guishing between them, the requirement relating to a leading single-
345 quote or double-quote applied to floating-point conversions even though
346 this provided no useful functionality to applications that was not
347 already available through the integer conversions. The current standard
348 clarifies the situation by specifying that the arguments for floating-
349 point conversions are evaluated as if by strtod(), and the arguments
350 for integer conversions are evaluated as C integer constants, with the
351 special treatment of leading single-quote and double-quote applying
352 only to integer conversions.
353
355 None.
356
358 awk, bc, echo
359 The Base Definitions volume of POSIX.1‐2008, Chapter 5, File Format
361 Notation, Chapter 8, Environment Variables
362 The System Interfaces volume of POSIX.1‐2008, fprintf(), strtod()
364
366 Portions of this text are reprinted and reproduced in electronic form
367 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
368 -- Portable Operating System Interface (POSIX), The Open Group Base
369 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
370 cal and Electronics Engineers, Inc and The Open Group. (This is
371 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
372 event of any discrepancy between this version and the original IEEE and
373 The Open Group Standard, the original IEEE and The Open Group Standard
374 is the referee document. The original Standard can be obtained online
375 at http://www.unix.org/online.html .
376 Any typographical or formatting errors that appear in this page are
378 most likely to have been introduced during the conversion of the source
379 files to man page format. To report such errors, see https://www.ker‐
380 nel.org/doc/man-pages/reporting_bugs.html .
381IEEE/The Open Group 2013 PRINTF(1P)