printf(1)printf(1)NAMEprintf - print formatted output
SYNOPSISprintf format [arg . . .]
DESCRIPTION
The printf command converts, formats, and prints its args under control
of the format. It fully supports conversion specifications for strings
(%s descriptor); however, the results are undefined for the other
conversion specifications not specifically mentioned below.
format a character string that contains three types of objects: 1)
plain characters, which are simply copied to the output stream;
2) conversion specifications, each of which results in fetching
zero or more args; and 3) C-language escape sequences, which
are translated into the corresponding characters.
arg string(s) to be printed under the control of format. The
results are undefined if there are insufficient args for the
format.
Each conversion specification is introduced by the character %. After
the %, the following appear in sequence:
An optional field, consisting of a decimal digit string followed by
a $, specifying the next arg to be converted. If this field is not
provided, the arg following the last arg converted is used.
An optional decimal digit string specifying a minimum field width.
If the converted value has fewer characters than the field width, it
is padded on the left (or right, if the left-adjustment flag `-' has
been given) to the field width. The padding is with blanks unless
the field width digit string starts with a zero, in which case the
padding is with zeros.
An optional precision that gives the maximum number of characters to
be printed from a string in %s conversion. The precision takes the
form of a period (.) followed by a decimal digit string; a null
digit string is treated as zero (nothing is printed). Padding
specified by the precision overrides the padding specified by the
field width. That is, if precision is specified, its value is used
to control the number of characters printed.
A field width or precision or both may be indicated by an asterisk
(*) instead of a digit string. In this case, an integer arg
supplies the field width or precision. The arg that is actually
converted is not fetched until the conversion letter is seen, so the
args specifying field width or precision must appear before the arg
(if any) to be converted. A negative field width argument is taken
as a `-' (left-adjustment) flag followed by a positive field width.
If the precision argument is negative, it is changed to zero
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(nothing is printed). In no case does a non-existent or small field
width cause truncation of a field; if the result of a conversion is
wider than the field width, the field is simply expanded to contain
the conversion result.
The conversion characters and their meanings are:
%e, %E, %f, %g and %G
These conversion specifications are not supported.
%b The argument will be taken to be a string that may contain
backslash-escape sequences.
%s The arg is taken to be a string and characters from the string are
printed until a null character (\0) is encountered or the number of
characters indicated by the precision specification is reached. If
the precision is missing, it is taken to be infinite, so all
characters up to the first null character are printed. A null value
for arg yields undefined results.
%% Print a %; no argument is converted.
EXTENDED DESCRIPTIONprintf does not precede or follow output from the %d or %u conversion
specifications with blank characters not specified by the format operand.
printf does not precede output from the %o conversion specification with
zeros not specified by the format operand.
The following backslash-escape sequences are supported:
File Format Notation (\\, \a, \b, \f, \n, \r, \t, \v), which will be
converted to the characters they represent.
\0ddd,
where ddd is a zero-, one-, two- or three-digit octal number that will be
converted to a byte with the numeric value specified by the octal
number\c, which will not be written and will 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 will be written until the end of the
string or the number of bytes indicated by the precision specification is
reached.
If the precision is omitted, it will be taken to be infinite, so all
bytes up to the end of the converted string will be written. For each
specification that consumes an argument, the next argument operand will
be evaluated and converted to the appropriate type for the conversion as
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specified below.
The format operand will be reused as often as necessary to satisfy the
argument operands.
Any extra %c or %s conversion specifications will be evaluated as if a
null string argument were supplied; other extra conversion specifications
will be evaluated as if a zero argument were supplied.
If the format operand contains no conversion 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 conversion specification, the behaviour is unspecified.The
argument operands will be treated as strings if the corresponding
conversion character is %b, %c or %s; otherwise, it will be evaluated as
a C constant, as described by the ISO C standard, with the following
extensions:
A leading plus or minus sign will be allowed.
If the leading character is a single- or double-quote, the value will be
the numeric value in the underlying codeset of the character following
the single- or double-quote.
If an argument operand cannot be completely converted into an internal
value appropriate to the corresponding conversion specification, a
diagnostic message will be written to standard error and the utility will
not exit with a zero exit status, but will continue processing any
remaining operands and will write the value accumulated at the time the
error was detected to standard output.
EXIT STATUS
The following exit values are returned:
0 Successful completion.
>0 An error occurred.
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. 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.
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 with 32-bit twos-complement integers when %d is
specified as the format operand:
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Diagnostic Output
printf: "5a" not completely converted
printf: "9999999999" arithmetic overflow
printf: "-9999999999" arithmetic overflow
printf: "ABC" expected numeric value
Note that the value shown on standard output is what would be expected as
the return value from the function strtol. A similar correspondence
exists between %u and strtoul.
EXAMPLES
The command
printf '%s %s %s\n' Good Morning World
results in the output:
Good Morning World
The following command produces the same output.
printf '%2$s %s %1$s\n' World Good Morning
Here is an example that prints the first 6 characters of $PATH left-
adjusted in a 10-character field:
printf 'First 6 chars of %s are %-10.6s.0 $PATH $PATH
If $PATH has the value /usr/bin:/usr/local/bin, then the above command
would print the following output:
First 6 chars of /usr/bin:/usr/local/bin are /usr/b .
To alert the user and then print and read a series of prompts:
printf "\aPlease fill in the following: \nName: "
read name
printf "Phone number: "
read phone
To read out a list of right and wrong answers from a file, calculate the
percentage correctly, and print them out. The numbers are right-
justified and separated by a single tab character. The percentage is
written to one decimal place of accuracy:
while read right wrong ; do
percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
printf "%2d right%2d wrong(%s%%)0 \
$right $wrong $percent
done < database_file
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The command:
printf "%5d%4d\n" 1 21 321 4321 54321
produces:
1 21
321 4321
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.
SEE ALSOprintf(3S)
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