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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
my $result = sprintf("%08d", $number);
# Round number to 3 digits after decimal point
my $rounded = sprintf("%.3f", $number);
Perl does its own "sprintf" formatting: 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.
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
%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 argument in the parameter list
%a hexadecimal floating point
%A like %a, but using upper-case letters
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". Similarly for %a and %A: the exponent or the
hexadecimal digits may float: especially the "long doubles" Perl
configuration option may cause surprises.
Between the "%" 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:
printf '%2$d %1$d', 12, 34; # prints "34 12"
printf '%3$d %d %1$d', 1, 2, 3; # prints "3 1 1"
flags
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"
For example:
printf '<% d>', 12; # prints "< 12>"
printf '<% d>', 0; # prints "< 0>"
printf '<% d>', -12; # prints "<-12>"
printf '<%+d>', 12; # prints "<+12>"
printf '<%+d>', 0; # prints "<+0>"
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,
the space is ignored.
printf '<%+ d>', 12; # prints "<+12>"
printf '<% +d>', 12; # prints "<+12>"
When the # flag and a precision are given in the %o
conversion, the precision is incremented if it's necessary
for the leading "0".
printf '<%#.5o>', 012; # prints "<00012>"
printf '<%#.5o>', 012345; # prints "<012345>"
printf '<%#.0o>', 0; # prints "<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:
printf "%vd", "AB\x{100}"; # prints "65.66.256"
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", " ", $bits; # random bitstring
You can also explicitly specify the argument number to use
for the join string using something like "*2$v"; for
example:
printf '%*4$vX %*4$vX %*4$vX', # 3 IPv6 addresses
@addr[1..3], ":";
(minimum) width
Arguments are usually formatted to be only as wide as
required to display the given value. You can override the
width by putting a number here, or get the width from the
next argument (with "*") or from a specified argument (e.g.,
with "*2$"):
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 except "g"
and "G", this specifies how many places right of the decimal
point to show (the default being 6). For example:
# 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 "g" and "G", this specifies the maximum number of
significant digits to show; 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>"
printf '<%.1g>', 0.0111; # prints "<0.01>"
printf '<%.2g>', 0.0111; # prints "<0.011>"
printf '<%.3g>', 0.0111; # prints "<0.0111>"
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:
printf '<%.5s>', "truncated"; # prints "<trunc>"
printf '<%10.5s>', "truncated"; # prints "< trunc>"
You can also get the precision from the next argument using
".*", or from a specified argument (e.g., with ".*2$"):
printf '<%.6x>', 1; # prints "<000001>"
printf '<%.*x>', 6, 1; # prints "<000001>"
printf '<%.*2$x>', 1, 6; # prints "<000001>"
printf '<%6.*2$x>', 1, 4; # prints "< 0001>"
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>"
size
For numeric conversions, you can specify the size to
interpret the number as using "l", "h", "V", "q", "L", or
"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:
hh interpret integer as C type "char" or "unsigned
char" on Perl 5.14 or later
h interpret integer as C type "short" or
"unsigned short"
j interpret integer as C type "intmax_t" on Perl
5.14 or later; and prior to Perl 5.30, only with
a C99 compiler (unportable)
l interpret integer as C type "long" or
"unsigned long"
q, L, or ll interpret integer as C type "long long",
"unsigned long long", or "quad" (typically
64-bit integers)
t interpret integer as C type "ptrdiff_t" on Perl
5.14 or later
z interpret integer as C types "size_t" or
"ssize_t" on Perl 5.14 or later
Note that, in general, using the "l" modifier (for example,
when writing "%ld" or "%lu" instead of "%d" and "%u") is
unnecessary when used from Perl code. Moreover, it may be
harmful, for example on Windows 64-bit where a long is
32-bits.
As of 5.14, none of these raises an exception if they are
not supported on your platform. However, if warnings are
enabled, a warning of the "printf" warning class is issued
on an unsupported conversion flag. Should you instead prefer
an exception, do this:
use warnings FATAL => "printf";
If you would like to know about a version dependency before
you start running the program, put something like this at
its top:
use 5.014; # for hh/j/t/z/ printf modifiers
You can find out whether your Perl supports quads via
Config:
use Config;
if ($Config{use64bitint} eq "define"
|| $Config{longsize} >= 8) {
print "Nice quads!\n";
}
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 "q", "L", or "ll" if your platform
supports them. You can find out whether your Perl supports
long doubles via Config:
use Config;
print "long doubles\n" if $Config{d_longdbl} eq "define";
You can find out whether Perl considers "long double" to be
the default floating-point size to use on your platform via
Config:
use Config;
if ($Config{uselongdouble} eq "define") {
print "long doubles by default\n";
}
It can also be that long doubles and doubles are the same
thing:
use Config;
($Config{doublesize} == $Config{longdblsize}) &&
print "doubles are long doubles\n";
The size specifier "V" has 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.
So:
printf "<%*.*s>", $a, $b, $c;
uses $a for the width, $b for the precision, and $c as the
value to format; while:
printf '<%*1$.*s>', $a, $b;
would use $a for the width and precision, and $b as the
value to format.
Here are some more examples; be aware that when using an
explicit index, the "$" may need escaping:
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"
printf "%*1\$.*f\n", 4, 5, 10; # will print "5.0000\n"
If "use locale" (including "use locale ':not_characters'") is 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.
Generated by phpMan Author: Che Dong Under GNU General Public License
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