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
12 printf — write formatted output
13
15 printf format [argument...]
16
18 The printf utility shall write formatted operands to the standard out‐
19 put. The argument operands shall be formatted under control of the for‐
20 mat operand.
21
23 None.
24
26 The following operands shall be supported:
27 format A string describing the format to use to write the remaining
29 operands. See the EXTENDED DESCRIPTION section.
30 argument The strings to be written to standard output, under the con‐
32 trol of format. See the EXTENDED DESCRIPTION section.
33
35 Not used.
36
38 None.
39
41 The following environment variables shall affect the execution of
42 printf:
43 LANG Provide a default value for the internationalization vari‐
45 ables that are unset or null. (See the Base Definitions vol‐
46 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
47 ables the precedence of internationalization variables used
48 to determine the values of locale categories.)
49 LC_ALL If set to a non-empty string value, override the values of
51 all the other internationalization variables.
52 LC_CTYPE Determine the locale for the interpretation of sequences of
54 bytes of text data as characters (for example, single-byte as
55 opposed to multi-byte characters in arguments).
56 LC_MESSAGES
58 Determine the locale that should be used to affect the format
59 and contents of diagnostic messages written to standard
60 error.
61 LC_NUMERIC
63 Determine the locale for numeric formatting. It shall affect
64 the format of numbers written using the e, E, f, g, and G
65 conversion specifier characters (if supported).
66 NLSPATH Determine the location of message catalogs for the processing
68 of LC_MESSAGES.
69
71 Default.
72
74 See the EXTENDED DESCRIPTION section.
75
77 The standard error shall be used only for diagnostic messages.
78
80 None.
81
83 The format operand shall be used as the format string described in the
84 Base Definitions volume of POSIX.1‐2017, Chapter 5, File Format Nota‐
85 tion with the following exceptions:
86 1. A <space> in the format string, in any context other than a flag of
88 a conversion specification, shall be treated as an ordinary charac‐
89 ter that is copied to the output.
90 2. A '' character in the format string shall be treated as a '' char‐
92 acter, not as a <space>.
93 3. In addition to the escape sequences shown in the Base Definitions
95 volume of POSIX.1‐2017, Chapter 5, File Format Notation ('\\',
96 '\a', '\b', '\f', '\n', '\r', '\t', '\v'), "\ddd", where ddd is a
97 one, two, or three-digit octal number, shall be written as a byte
98 with the numeric value specified by the octal number.
99 4. The implementation shall not precede or follow output from the d or
101 u conversion specifiers with <blank> characters not specified by
102 the format operand.
103 5. The implementation shall not precede output from the o conversion
105 specifier with zeros not specified by the format operand.
106 6. The a, A, e, E, f, F, g, and G conversion specifiers need not be
108 supported.
109 7. An additional conversion specifier character, b, shall be supported
111 as follows. The argument shall be taken to be a string that can
112 contain <backslash>-escape sequences. The following <back‐
113 slash>-escape sequences shall be supported:
114 -- The escape sequences listed in the Base Definitions volume of
116 POSIX.1‐2017, Chapter 5, File Format Notation ('\\', '\a',
117 '\b', '\f', '\n', '\r', '\t', '\v'), which shall be converted
118 to the characters they represent
119 -- "\0ddd", where ddd is a zero, one, two, or three-digit octal
121 number that shall be converted to a byte with the numeric value
122 specified by the octal number
123 -- '\c', which shall not be written and shall cause printf to
125 ignore any remaining characters in the string operand contain‐
126 ing it, any remaining string operands, and any additional char‐
127 acters in the format operand
128 The interpretation of a <backslash> followed by any other sequence
130 of characters is unspecified.
131 Bytes from the converted string shall be written until the end of
133 the string or the number of bytes indicated by the precision speci‐
134 fication is reached. If the precision is omitted, it shall be taken
135 to be infinite, so all bytes up to the end of the converted string
136 shall be written.
137 8. For each conversion specification that consumes an argument, the
139 next argument operand shall be evaluated and converted to the
140 appropriate type for the conversion as specified below.
141 9. The format operand shall be reused as often as necessary to satisfy
143 the argument operands. Any extra b, c, or s conversion specifiers
144 shall be evaluated as if a null string argument were supplied;
145 other extra conversion specifications shall be evaluated as if a
146 zero argument were supplied. If the format operand contains no con‐
147 version specifications and argument operands are present, the
148 results are unspecified.
149 10. If a character sequence in the format operand begins with a '%'
151 character, but does not form a valid conversion specification, the
152 behavior is unspecified.
153 11. The argument to the c conversion specifier can be a string contain‐
155 ing zero or more bytes. If it contains one or more bytes, the first
156 byte shall be written and any additional bytes shall be ignored. If
157 the argument is an empty string, it is unspecified whether nothing
158 is written or a null byte is written.
159 The argument operands shall be treated as strings if the corresponding
161 conversion specifier is b, c, or s, and shall be evaluated as if by the
162 strtod() function if the corresponding conversion specifier is a, A, e,
163 E, f, F, g, or G. Otherwise, they shall be evaluated as unsuffixed C
164 integer constants, as described by the ISO C standard, with the follow‐
165 ing extensions:
166 * A leading <plus-sign> or <hyphen-minus> shall be allowed.
168 * If the leading character is a single-quote or double-quote, the
170 value shall be the numeric value in the underlying codeset of the
171 character following the single-quote or double-quote.
172 * Suffixed integer constants may be allowed.
174 If an argument operand cannot be completely converted into an internal
176 value appropriate to the corresponding conversion specification, a
177 diagnostic message shall be written to standard error and the utility
178 shall not exit with a zero exit status, but shall continue processing
179 any remaining operands and shall write the value accumulated at the
180 time the error was detected to standard output.
181 It shall not be considered an error if an argument operand is not com‐
183 pletely used for a b, c, or s conversion.
184
186 The following exit values shall be returned:
187 0 Successful completion.
189 >0 An error occurred.
191
193 Default.
194 The following sections are informative.
196
198 The floating-point formatting conversion specifications of printf() are
199 not required because all arithmetic in the shell is integer arithmetic.
200 The awk utility performs floating-point calculations and provides its
201 own printf function. The bc utility can perform arbitrary-precision
202 floating-point arithmetic, but does not provide extensive formatting
203 capabilities. (This printf utility cannot really be used to format bc
204 output; it does not support arbitrary precision.) Implementations are
205 encouraged to support the floating-point conversions as an extension.
206 Note that this printf utility, like the printf() function defined in
208 the System Interfaces volume of POSIX.1‐2017 on which it is based,
209 makes no special provision for dealing with multi-byte characters when
210 using the %c conversion specification or when a precision is specified
211 in a %b or %s conversion specification. Applications should be
212 extremely cautious using either of these features when there are multi-
213 byte characters in the character set.
214 No provision is made in this volume of POSIX.1‐2017 which allows field
216 widths and precisions to be specified as '*' since the '*' can be
217 replaced directly in the format operand using shell variable substitu‐
218 tion. Implementations can also provide this feature as an extension if
219 they so choose.
220 Hexadecimal character constants as defined in the ISO C standard are
222 not recognized in the format operand because there is no consistent way
223 to detect the end of the constant. Octal character constants are lim‐
224 ited to, at most, three octal digits, but hexadecimal character con‐
225 stants are only terminated by a non-hex-digit character. In the ISO C
226 standard, the "##" concatenation operator can be used to terminate a
227 constant and follow it with a hexadecimal character to be written. In
228 the shell, concatenation occurs before the printf utility has a chance
229 to parse the end of the hexadecimal constant.
230 The %b conversion specification is not part of the ISO C standard; it
232 has been added here as a portable way to process <backslash>-escapes
233 expanded in string operands as provided by the echo utility. See also
234 the APPLICATION USAGE section of echo for ways to use printf as a
235 replacement for all of the traditional versions of the echo utility.
236 If an argument cannot be parsed correctly for the corresponding conver‐
238 sion specification, the printf utility is required to report an error.
239 Thus, overflow and extraneous characters at the end of an argument
240 being used for a numeric conversion shall be reported as errors.
241
243 To alert the user and then print and read a series of prompts:
244 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
258 percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
259 printf "%2d right\t%2d wrong\t(%s%%)\n" \
260 $right $wrong $percent
261 done < database_file
262 The command:
264 printf "%5d%4d\n" 1 21 321 4321 54321
267 produces:
269 1 21
272 3214321
273 54321 0
274 Note that the format operand is used three times to print all of the
276 given strings and that a '0' was supplied by printf to satisfy the last
277 %4d conversion specification.
278 The printf utility is required to notify the user when conversion
280 errors are detected while producing numeric output; thus, the following
281 results would be expected on an implementation with 32-bit twos-comple‐
282 ment integers when %d is specified as the format operand:
283 ┌────────────┬─────────────┬───────────────────────────────────────────┐
285 │ │ Standard │ │
286 │ Argument │ Output │ Diagnostic Output │
287 ├────────────┼─────────────┼───────────────────────────────────────────┤
288 │5a │ 5 │ printf: "5a" not completely converted │
289 │9999999999 │ 2147483647 │ printf: "9999999999" arithmetic overflow │
290 │-9999999999 │ -2147483648 │ printf: "-9999999999" arithmetic overflow │
291 │ABC │ 0 │ printf: "ABC" expected numeric value │
292 └────────────┴─────────────┴───────────────────────────────────────────┘
293 The diagnostic message format is not specified, but these examples con‐
294 vey the type of information that should be reported. Note that the
295 value shown on standard output is what would be expected as the return
296 value from the strtol() function as defined in the System Interfaces
297 volume of POSIX.1‐2017. A similar correspondence exists between %u and
298 strtoul() and %e, %f, and %g (if the implementation supports floating-
299 point conversions) and strtod().
300 In a locale using the ISO/IEC 646:1991 standard as the underlying code‐
302 set, the command:
303 printf "%d\n" 3 +3 -3 \'3 \"+3 "'-3"
306 produces:
308 3 Numeric value of constant 3
310 3 Numeric value of constant 3
312 -3 Numeric value of constant -3
314 51 Numeric value of the character '3' in the ISO/IEC 646:1991 stan‐
316 dard codeset
317 43 Numeric value of the character '+' in the ISO/IEC 646:1991 stan‐
319 dard codeset
320 45 Numeric value of the character '-' in the ISO/IEC 646:1991 stan‐
322 dard codeset
323 Note that in a locale with multi-byte characters, the value of a char‐
325 acter is intended to be the value of the equivalent of the wchar_t rep‐
326 resentation of the character as described in the System Interfaces vol‐
327 ume of POSIX.1‐2017.
328
330 The printf utility was added to provide functionality that has histori‐
331 cally been provided by echo. However, due to irreconcilable differ‐
332 ences in the various versions of echo extant, the version has few spe‐
333 cial features, leaving those to this new printf utility, which is based
334 on one in the Ninth Edition system.
335 The EXTENDED DESCRIPTION section almost exactly matches the printf()
337 function in the ISO C standard, although it is described in terms of
338 the file format notation in the Base Definitions volume of
339 POSIX.1‐2017, Chapter 5, File Format Notation.
340 Earlier versions of this standard specified that arguments for all con‐
342 versions other than b, c, and s were evaluated in the same way (as C
343 constants, but with stated exceptions). For implementations supporting
344 the floating-point conversions it was not clear whether integer conver‐
345 sions need only accept integer constants and floating-point conversions
346 need only accept floating-point constants, or whether both types of
347 conversions should accept both types of constants. Also by not distin‐
348 guishing between them, the requirement relating to a leading single-
349 quote or double-quote applied to floating-point conversions even though
350 this provided no useful functionality to applications that was not
351 already available through the integer conversions. The current standard
352 clarifies the situation by specifying that the arguments for floating-
353 point conversions are evaluated as if by strtod(), and the arguments
354 for integer conversions are evaluated as C integer constants, with the
355 special treatment of leading single-quote and double-quote applying
356 only to integer conversions.
357
359 None.
360
362 awk, bc, echo
363 The Base Definitions volume of POSIX.1‐2017, Chapter 5, File Format
365 Notation, Chapter 8, Environment Variables
366 The System Interfaces volume of POSIX.1‐2017, fprintf(), strtod()
368
370 Portions of this text are reprinted and reproduced in electronic form
371 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
372 table Operating System Interface (POSIX), The Open Group Base Specifi‐
373 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
374 Electrical and Electronics Engineers, Inc and The Open Group. In the
375 event of any discrepancy between this version and the original IEEE and
376 The Open Group Standard, the original IEEE and The Open Group Standard
377 is the referee document. The original Standard can be obtained online
378 at http://www.opengroup.org/unix/online.html .
379 Any typographical or formatting errors that appear in this page are
381 most likely to have been introduced during the conversion of the source
382 files to man page format. To report such errors, see https://www.ker‐
383 nel.org/doc/man-pages/reporting_bugs.html .
384IEEE/The Open Group 2017 PRINTF(1P)