Perl 5 version 12.1 documentation
- sprintf FORMAT, LIST
Returns a string formatted by the usual
printfconventions of the C library function
sprintf. See below for more details and see
printf(3)on your system for an explanation of the general principles.
Perl does its own
sprintfformatting: it emulates the C function sprintf(3), but doesn't use it except for floating-point numbers, and even then only standard modifiers are allowed. Non-standard extensions in your local sprintf(3) are therefore unavailable from Perl.
sprintfdoes not do what you probably mean when you pass it an array as your first argument. The array is given scalar context, and instead of using the 0th element of the array as the format, Perl will use the count of elements in the array as the format, which is almost never useful.
sprintfpermits the following universally-known conversions:
- %% a percent sign
- %c a character with the given number
- %s a string
- %d a signed integer, in decimal
- %u an unsigned integer, in decimal
- %o an unsigned integer, in octal
- %x an unsigned integer, in hexadecimal
- %e a floating-point number, in scientific notation
- %f a floating-point number, in fixed decimal notation
- %g a floating-point number, in %e or %f notation
In addition, Perl permits the following widely-supported conversions:
- %X like %x, but using upper-case letters
- %E like %e, but using an upper-case "E"
- %G like %g, but with an upper-case "E" (if applicable)
- %b an unsigned integer, in binary
- %B like %b, but using an upper-case "B" with the # flag
- %p a pointer (outputs the Perl value's address in hexadecimal)
- %n special: *stores* the number of characters output so far
- into the next variable in the parameter list
Finally, for backward (and we do mean "backward") compatibility, Perl permits these unnecessary but widely-supported conversions:
- %i a synonym for %d
- %D a synonym for %ld
- %U a synonym for %lu
- %O a synonym for %lo
- %F a synonym for %f
Note that the number of exponent digits in the scientific notation produced by
%Gfor numbers with the modulus of the exponent less than 100 is system-dependent: it may be three or less (zero-padded as necessary). In other words, 1.23 times ten to the 99th may be either "1.23e99" or "1.23e099".
%and the format letter, you may specify several additional attributes controlling the interpretation of the format. In order, these are:
- format parameter index
An explicit format parameter index, such as
2$. By default sprintf will format the next unused argument in the list, but this allows you to take the arguments out of order:
one or more of:
- space prefix non-negative number with a space
- + prefix non-negative number with a plus sign
- - left-justify within the field
- 0 use zeros, not spaces, to right-justify
- # ensure the leading "0" for any octal,
- prefix non-zero hexadecimal with "0x" or "0X",
- prefix non-zero binary with "0b" or "0B"
- printf '<% d>', 12; # prints "< 12>"
- printf '<%+d>', 12; # prints "<+12>"
- printf '<%6s>', 12; # prints "< 12>"
- printf '<%-6s>', 12; # prints "<12 >"
- printf '<%06s>', 12; # prints "<000012>"
- printf '<%#o>', 12; # prints "<014>"
- printf '<%#x>', 12; # prints "<0xc>"
- printf '<%#X>', 12; # prints "<0XC>"
- printf '<%#b>', 12; # prints "<0b1100>"
- printf '<%#B>', 12; # prints "<0B1100>"
When a space and a plus sign are given as the flags at once, a plus sign is used to prefix a positive number.
When the # flag and a precision are given in the %o conversion, the precision is incremented if it's necessary for the leading "0".
- vector flag
This flag tells Perl to interpret the supplied string as a vector of integers, one for each character in the string. Perl applies the format to each integer in turn, then joins the resulting strings with a separator (a dot
.by default). This can be useful for displaying ordinal values of characters in arbitrary strings:
Put an asterisk
vto override the string to use to separate the numbers:
You can also explicitly specify the argument number to use for the join string using something like
*2$v; for example:
- printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":"; # 3 IPv6 addresses
- (minimum) width
Arguments are usually formatted to be only as wide as required to display the given value. You can override the width by putting a number here, or get the width from the next argument (with
*) or from a specified argument (e.g., with
If a field width obtained through
*is negative, it has the same effect as the
- precision, or maximum width
You can specify a precision (for numeric conversions) or a maximum width (for string conversions) by specifying a
.followed by a number. For floating-point formats except 'g' and 'G', this specifies how many places right of the decimal point to show (the default being 6). For example:
For "g" and "G", this specifies the maximum number of digits to show, including thoe prior to the decimal point and those after it; for example:
- # These examples are subject to system-specific variation.
- printf '<%g>', 1; # prints "<1>"
- printf '<%.10g>', 1; # prints "<1>"
- printf '<%g>', 100; # prints "<100>"
- printf '<%.1g>', 100; # prints "<1e+02>"
- printf '<%.2g>', 100.01; # prints "<1e+02>"
- printf '<%.5g>', 100.01; # prints "<100.01>"
- printf '<%.4g>', 100.01; # prints "<100>"
For integer conversions, specifying a precision implies that the output of the number itself should be zero-padded to this width, where the 0 flag is ignored:
- printf '<%.6d>', 1; # prints "<000001>"
- printf '<%+.6d>', 1; # prints "<+000001>"
- printf '<%-10.6d>', 1; # prints "<000001 >"
- printf '<%10.6d>', 1; # prints "< 000001>"
- printf '<%010.6d>', 1; # prints "< 000001>"
- printf '<%+10.6d>', 1; # prints "< +000001>"
- printf '<%.6x>', 1; # prints "<000001>"
- printf '<%#.6x>', 1; # prints "<0x000001>"
- printf '<%-10.6x>', 1; # prints "<000001 >"
- printf '<%10.6x>', 1; # prints "< 000001>"
- printf '<%010.6x>', 1; # prints "< 000001>"
- printf '<%#10.6x>', 1; # prints "< 0x000001>"
For string conversions, specifying a precision truncates the string to fit the specified width:
You can also get the precision from the next argument using
If a precision obtained through
*is negative, it counts as having no precision at all.
- printf '<%.*s>', 7, "string"; # prints "<string>"
- printf '<%.*s>', 3, "string"; # prints "<str>"
- printf '<%.*s>', 0, "string"; # prints "<>"
- printf '<%.*s>', -1, "string"; # prints "<string>"
- printf '<%.*d>', 1, 0; # prints "<0>"
- printf '<%.*d>', 0, 0; # prints "<>"
- printf '<%.*d>', -1, 0; # prints "<0>"
You cannot currently get the precision from a specified number, but it is intended that this will be possible in the future, for example using
- printf "<%.*2$x>", 1, 6; # INVALID, but in future will print "<000001>"
For numeric conversions, you can specify the size to interpret the number as using
ll. For integer conversions (
d u o x X b i D U O), numbers are usually assumed to be whatever the default integer size is on your platform (usually 32 or 64 bits), but you can override this to use instead one of the standard C types, as supported by the compiler used to build Perl:
- l interpret integer as C type "long" or "unsigned long"
- h interpret integer as C type "short" or "unsigned short"
- q, L or ll interpret integer as C type "long long", "unsigned long long".
- or "quads" (typically 64-bit integers)
The last will raise an exception if Perl does not understand "quads" in your installation. (This requires either that the platform natively support quads, or that Perl were specifically compiled to support quads.) You can find out whether your Perl supports quads via Config:
For floating-point conversions (
e f g E F G), numbers are usually assumed to be the default floating-point size on your platform (double or long double), but you can force "long double" with
llif your platform supports them. You can find out whether your Perl supports long doubles via Config:
You can find out whether Perl considers "long double" to be the default floating-point size to use on your platform via Config:
It can also be that long doubles and doubles are the same thing:
The size specifier
Vhas no effect for Perl code, but is supported for compatibility with XS code. It means "use the standard size for a Perl integer or floating-point number", which is the default.
- order of arguments
Normally, sprintf() takes the next unused argument as the value to format for each format specification. If the format specification uses
*to require additional arguments, these are consumed from the argument list in the order they appear in the format specification before the value to format. Where an argument is specified by an explicit index, this does not affect the normal order for the arguments, even when the explicitly specified index would have been the next argument.
- printf "<%*.*s>", $a, $b, $c;
$afor the width,
$bfor the precision, and
$cas the value to format; while:
- printf "<%*1$.*s>", $a, $b;
$afor the width and precision, and
$bas the value to format.
Here are some more examples; be aware that when using an explicit index, the
$may need escaping:
use localeis in effect and POSIX::setlocale() has been called, the character used for the decimal separator in formatted floating-point numbers is affected by the LC_NUMERIC locale. See perllocale and POSIX.