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 op‐
29 erands. See the EXTENDED DESCRIPTION section.
30 argument
32 The strings to be written to standard output, under the control
33 of format. See the EXTENDED DESCRIPTION section.
34
37 Not used.
38
40 None.
41
43 The following environment variables shall affect the execution of
44 printf:
45 LANG Provide a default value for the internationalization variables
47 that are unset or null. (See the Base Definitions volume of
48 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
49 ables for the precedence of internationalization variables used
50 to determine the values of locale categories.)
51 LC_ALL If set to a non-empty string value, override the values of all
53 the other internationalization variables.
54 LC_CTYPE
56 Determine the locale for the interpretation of sequences of
57 bytes of text data as characters (for example, single-byte as
58 opposed to multi-byte characters in arguments).
59 LC_MESSAGES
61 Determine the locale that should be used to affect the format
62 and contents of diagnostic messages written to standard error.
63 LC_NUMERIC
65 Determine the locale for numeric formatting. It shall affect the
67 format of numbers written using the e, E, f, g, and G conversion
68 specifier characters (if supported).
69 NLSPATH
71 Determine the location of message catalogs for the processing of
72 LC_MESSAGES .
73
76 Default.
77
79 See the EXTENDED DESCRIPTION section.
80
82 The standard error shall be used only for diagnostic messages.
83
85 None.
86
88 The format operand shall be used as the format string described in the
89 Base Definitions volume of IEEE Std 1003.1-2001, Chapter 5, File Format
90 Notation with the following exceptions:
91 1. A <space> in the format string, in any context other than a flag of
93 a conversion specification, shall be treated as an ordinary charac‐
94 ter that is copied to the output.
95 2. A ' ' character in the format string shall be treated as a ' '
97 character, not as a <space>.
98 3. In addition to the escape sequences shown in the Base Definitions
100 volume of IEEE Std 1003.1-2001, Chapter 5, File Format Notation (
101 '\\', '\a', '\b', '\f', '\n', '\r', '\t', '\v' ), "\ddd", where ddd
102 is a one, two, or three-digit octal number, shall be written as a
103 byte with the numeric value specified by the octal number.
104 4. The implementation shall not precede or follow output from the d or
106 u conversion specifiers with <blank>s not specified by the format
107 operand.
108 5. The implementation shall not precede output from the o conversion
110 specifier with zeros not specified by the format operand.
111 6. The e, E, f, g, and G conversion specifiers need not be supported.
113 7. An additional conversion specifier character, b, shall be supported
115 as follows. The argument shall be taken to be a string that may
116 contain backslash-escape sequences. The following backslash-escape
117 sequences shall be supported:
118 * The escape sequences listed in the Base Definitions volume of
120 IEEE Std 1003.1-2001, Chapter 5, File Format Notation ( '\\',
121 '\a', '\b', '\f', '\n', '\r', '\t', '\v' ), which shall be con‐
122 verted to the characters they represent
123 * "\0ddd", where ddd is a zero, one, two, or three-digit octal
125 number that shall be converted to a byte with the numeric value
126 specified by the octal number
127 * '\c', which shall not be written and shall cause printf to
129 ignore any remaining characters in the string operand containing
130 it, any remaining string operands, and any additional characters
131 in the format operand
132 The interpretation of a backslash followed by any other sequence of
134 characters is unspecified.
135 Bytes from the converted string shall be written until the end of the
137 string or the number of bytes indicated by the precision specification
138 is reached. If the precision is omitted, it shall be taken to be infi‐
139 nite, so all bytes up to the end of the converted string shall be writ‐
140 ten.
141 8. For each conversion specification that consumes an argument, the
143 next argument operand shall be evaluated and converted to the
144 appropriate type for the conversion as specified below.
145 9. The format operand shall be reused as often as necessary to satisfy
147 the argument operands. Any extra c or s conversion specifiers shall
148 be evaluated as if a null string argument were supplied; other
149 extra conversion specifications shall be evaluated as if a zero
150 argument were supplied. If the format operand contains no conver‐
151 sion specifications and argument operands are present, the results
152 are unspecified.
153 10. If a character sequence in the format operand begins with a '%'
155 character, but does not form a valid conversion specification, the
156 behavior is unspecified.
157 The argument operands shall be treated as strings if the corresponding
159 conversion specifier is b, c, or s ; otherwise, it shall be evaluated
160 as a C constant, as described by the ISO C standard, with the following
161 extensions:
162 * A leading plus or minus sign shall be allowed.
164 * If the leading character is a single-quote or double-quote, the
166 value shall be the numeric value in the underlying codeset of the
167 character following the single-quote or double-quote.
168 If an argument operand cannot be completely converted into an internal
170 value appropriate to the corresponding conversion specification, a
171 diagnostic message shall be written to standard error and the utility
172 shall not exit with a zero exit status, but shall continue processing
173 any remaining operands and shall write the value accumulated at the
174 time the error was detected to standard output.
175 It is not considered an error if an argument operand is not completely
177 used for a c or s conversion or if a string operand's first or second
178 character is used to get the numeric value of a character.
179
181 The following exit values shall be returned:
182 0 Successful completion.
184 >0 An error occurred.
186
189 Default.
190 The following sections are informative.
192
194 The floating-point formatting conversion specifications of printf() are
195 not required because all arithmetic in the shell is integer arithmetic.
196 The awk utility performs floating-point calculations and provides its
197 own printf function. The bc utility can perform arbitrary-precision
198 floating-point arithmetic, but does not provide extensive formatting
199 capabilities. (This printf utility cannot really be used to format bc
200 output; it does not support arbitrary precision.) Implementations are
201 encouraged to support the floating-point conversions as an extension.
202 Note that this printf utility, like the printf() function defined in
204 the System Interfaces volume of IEEE Std 1003.1-2001 on which it is
205 based, makes no special provision for dealing with multi-byte charac‐
206 ters when using the %c conversion specification or when a precision is
207 specified in a %b or %s conversion specification. Applications should
208 be extremely cautious using either of these features when there are
209 multi-byte characters in the character set.
210 No provision is made in this volume of IEEE Std 1003.1-2001 which
212 allows field widths and precisions to be specified as '*' since the '*'
213 can be replaced directly in the format operand using shell variable
214 substitution. Implementations can also provide this feature as an
215 extension if they so choose.
216 Hexadecimal character constants as defined in the ISO C standard are
218 not recognized in the format operand because there is no consistent way
219 to detect the end of the constant. Octal character constants are lim‐
220 ited to, at most, three octal digits, but hexadecimal character con‐
221 stants are only terminated by a non-hex-digit character. In the ISO C
222 standard, the "##" concatenation operator can be used to terminate a
223 constant and follow it with a hexadecimal character to be written. In
224 the shell, concatenation occurs before the printf utility has a chance
225 to parse the end of the hexadecimal constant.
226 The %b conversion specification is not part of the ISO C standard; it
228 has been added here as a portable way to process backslash escapes
229 expanded in string operands as provided by the echo utility. See also
230 the APPLICATION USAGE section of echo for ways to use printf as a
231 replacement for all of the traditional versions of the echo utility.
232 If an argument cannot be parsed correctly for the corresponding conver‐
234 sion specification, the printf utility is required to report an error.
235 Thus, overflow and extraneous characters at the end of an argument
236 being used for a numeric conversion shall be reported as errors.
237
239 To alert the user and then print and read a series of prompts:
240 printf "\aPlease fill in the following: \nName: "
243 read name
244 printf "Phone number: "
245 read phone
246 To read out a list of right and wrong answers from a file, calculate
248 the percentage correctly, and print them out. The numbers are right-
249 justified and separated by a single <tab>. The percentage is written to
250 one decimal place of accuracy:
251 while read right wrong ; do
254 percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
255 printf "%2d right\t%2d wrong\t(%s%%)\n" \
256 $right $wrong $percent
257 done < database_file
258 The command:
259 printf "%5d%4d\n" 1 21 321 4321 54321
262 produces:
264 1 21
267 3214321
268 54321 0
269 Note that the format operand is used three times to print all of the
271 given strings and that a '0' was supplied by printf to satisfy the last
272 %4d conversion specification.
273 The printf utility is required to notify the user when conversion
275 errors are detected while producing numeric output; thus, the following
276 results would be expected on an implementation with 32-bit twos-comple‐
277 ment integers when %d is specified as the format operand:
278 Standard
280 Argument Output Diagnostic Output
281 5a 5 printf: "5a" not completely converted
282 9999999999 2147483647 printf: "9999999999" arithmetic overflow
283 -9999999999 -2147483648 printf: "-9999999999" arithmetic overflow
284 ABC 0 printf: "ABC" expected numeric value
285 The diagnostic message format is not specified, but these examples con‐
287 vey the type of information that should be reported. Note that the
288 value shown on standard output is what would be expected as the return
289 value from the strtol() function as defined in the System Interfaces
290 volume of IEEE Std 1003.1-2001. A similar correspondence exists between
291 %u and strtoul() and %e, %f, and %g (if the implementation supports
292 floating-point conversions) and strtod().
293 In a locale using the ISO/IEC 646:1991 standard as the underlying code‐
295 set, the command:
296 printf "%d\n" 3 +3 -3 \'3 \"+3 "'-3"
299 produces:
301 3 Numeric value of constant 3
303 3 Numeric value of constant 3
305 -3 Numeric value of constant -3
307 51 Numeric value of the character '3' in the ISO/IEC 646:1991 stan‐
309 dard codeset
310 43 Numeric value of the character '+' in the ISO/IEC 646:1991 stan‐
312 dard codeset
313 45 Numeric value of the character '-' in the ISO/IEC 646:1991 stan‐
315 dard codeset
316 Note that in a locale with multi-byte characters, the value of a char‐
319 acter is intended to be the value of the equivalent of the wchar_t rep‐
320 resentation of the character as described in the System Interfaces vol‐
321 ume of IEEE Std 1003.1-2001.
322
324 The printf utility was added to provide functionality that has histori‐
325 cally been provided by echo. However, due to irreconcilable differences
326 in the various versions of echo extant, the version has few special
327 features, leaving those to this new printf utility, which is based on
328 one in the Ninth Edition system.
329 The EXTENDED DESCRIPTION section almost exactly matches the printf()
331 function in the ISO C standard, although it is described in terms of
332 the file format notation in the Base Definitions volume of
333 IEEE Std 1003.1-2001, Chapter 5, File Format Notation.
334
336 None.
337
339 awk, bc, echo, the System Interfaces volume of IEEE Std 1003.1-2001,
340 printf()
341
343 Portions of this text are reprinted and reproduced in electronic form
344 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
345 -- Portable Operating System Interface (POSIX), The Open Group Base
346 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
347 Electrical and Electronics Engineers, Inc and The Open Group. In the
348 event of any discrepancy between this version and the original IEEE and
349 The Open Group Standard, the original IEEE and The Open Group Standard
350 is the referee document. The original Standard can be obtained online
351 at http://www.opengroup.org/unix/online.html .
352IEEE/The Open Group 2003 PRINTF(1P)