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sprintf FORMAT, LIST

Returns a string formatted by the usual printf conventions of the C library function sprintf. See below for more details and see sprintf(3) or printf(3) on your system for an explanation of the general principles.

For example:

# Format number with up to 8 leading zeroes
$result = sprintf("%08d", $number);

# Round number to 3 digits after decimal point
$rounded = sprintf("%.3f", $number);

Perl does its own sprintf formatting--it emulates the C function sprintf, but it doesn't use it (except for floating-point numbers, and even then only the standard modifiers are allowed). As a result, any non-standard extensions in your local sprintf are not available from Perl.

Unlike printf, sprintf does 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.

Perl's sprintf permits 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
%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 %e, %E, %g and %G for 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".

Between the % and the format letter, you may specify a number of 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. Eg:

printf '%2$d %1$d', 12, 34;      # prints "34 12"
printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"

one or more of: space prefix positive number with a space + prefix positive number with a plus sign - left-justify within the field 0 use zeros, not spaces, to right-justify # prefix non-zero octal with "0", non-zero hex with "0x", non-zero binary with "0b"

For example:

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 '<%#x>', 12;   # prints "<0xc>"
vector flag

The vector flag v, optionally specifying the join string to use. This flag tells perl to interpret the supplied string as a vector of integers, one for each character in the string, separated by a given string (a dot . by default). This can be useful for displaying ordinal values of characters in arbitrary strings:

printf "version is v%vd\n", $^V;     # Perl's version

Put an asterisk * before the v to override the string to use to separate the numbers:

printf "address is %*vX\n", ":", $addr;   # IPv6 address
printf "bits are %0*v8b\n", " ", $bits;   # random bitstring

You can also explicitly specify the argument number to use for the join string using eg *2$v:

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 (with eg *2$):

printf '<%s>', "a";       # prints "<a>"
printf '<%6s>', "a";      # prints "<     a>"
printf '<%*s>', 6, "a";   # prints "<     a>"
printf '<%*2$s>', "a", 6; # prints "<     a>"
printf '<%2s>', "long";   # prints "<long>" (does not truncate)

If a field width obtained through * is negative, it has the same effect as the - flag: left-justification.

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, this specifies the number of decimal places to show (the default being 6), eg:

# these examples are subject to system-specific variation
printf '<%f>', 1;    # prints "<1.000000>"
printf '<%.1f>', 1;  # prints "<1.0>"
printf '<%.0f>', 1;  # prints "<1>"
printf '<%e>', 10;   # prints "<1.000000e+01>"
printf '<%.1e>', 10; # prints "<1.0e+01>"

For integer conversions, specifying a precision implies that the output of the number itself should be zero-padded to this width:

printf '<%.6x>', 1;      # prints "<000001>"
printf '<%#.6x>', 1;     # prints "<0x000001>"
printf '<%-10.6x>', 1;   # prints "<000001    >"

For string conversions, specifying a precision truncates the string to fit in the specified width:

printf '<%.5s>', "truncated";   # prints "<trunc>"
printf '<%10.5s>', "truncated"; # prints "<     trunc>"

You can also get the precision from the next argument using .*:

printf '<%.6x>', 1;       # prints "<000001>"
printf '<%.*x>', 6, 1;    # prints "<000001>"

You cannot currently get the precision from a specified number, but it is intended that this will be possible in the future using eg .*2$:

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 l, h, V, q, L or ll. For integer conversions, 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" or "unsigned long long"
            (if your platform supports such a type, else it is an error)

For floating point conversions, 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 q, L or ll if your platform supports them.

The size specifier 'V' has no effect for Perl code, but it supported for compatibility with XS code; it means 'use the standard size for a Perl integer (or floating-point number)', which is already the default for Perl code.

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 in which they appear in the format specification before the value to format. Where an argument is specified using 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 in any case).


printf '<%*.*s>', $a, $b, $c;

would use $a for the width, $b for the precision and $c as the value to format, while:

print '<%*1$.*s>', $a, $b;

would use $a for the width and the precision, and $b as the value to format.

Here are some more examples - beware that when using an explicit index, the $ may need to be escaped:

printf "%2\$d %d\n",    12, 34;		# will print "34 12\n"
printf "%2\$d %d %d\n", 12, 34;		# will print "34 12 34\n"
printf "%3\$d %d %d\n", 12, 34, 56;		# will print "56 12 34\n"
printf "%2\$*3\$d %d\n", 12, 34, 3;		# will print " 34 12\n"

If use locale is in effect, the character used for the decimal point in formatted real numbers is affected by the LC_NUMERIC locale. See perllocale.

If Perl understands "quads" (64-bit integers) (this requires either that the platform natively support quads or that Perl be specifically compiled to support quads), the characters

d u o x X b i D U O

print quads, and they may optionally be preceded by

ll L q

For example

%lld %16LX %qo

You can find out whether your Perl supports quads via Config:

use Config;
($Config{use64bitint} eq 'define' || $Config{longsize} == 8) &&
	print "quads\n";

If Perl understands "long doubles" (this requires that the platform support long doubles), the flags

e f g E F G

may optionally be preceded by

ll L

For example

%llf %Lg

You can find out whether your Perl supports long doubles via Config:

use Config;
$Config{d_longdbl} eq 'define' && print "long doubles\n";