Returns a string formatted by the usual
printf conventions of the C
sprintf. See below for more details
and see sprintf(3) or printf(3) on your system for an explanation of
the general principles.
Perl does its own
sprintf formatting--it emulates the C
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.
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
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
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".
and the format letter, you may specify a number of
additional attributes controlling the interpretation of the format.
In order, these are:
An explicit format parameter index, such as
2$. By default sprintf
will format the next unused argument in the list, but this allows you
to take the arguments out of order, e.g.:
one or more of: space prefix positive number with a space + prefix positive number with a plus sign - left-justify within the field 0 use zeros, not spaces, to right-justify # prefix non-zero octal with "0", non-zero hex with "0x", non-zero binary with "0b"
This flag tells perl to interpret the supplied string as a vector of
integers, one for each character in the string. Perl applies the format to
each integer in turn, then joins the resulting strings with a separator (a
. by default). This can be useful for displaying ordinal values of
characters in arbitrary strings:
Put an asterisk
to override the string to
use to separate the numbers:
You can also explicitly specify the argument number to use for
the join string using e.g.
- printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":"; # 3 IPv6 addresses
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 e.g.
If a field width obtained through
is negative, it has the same
effect as the
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, with the exception of 'g' and 'G', this specifies
the number of decimal places to show (the default being 6), e.g.:
For 'g' and 'G', this specifies the maximum number of digits to show, including prior to the decimal point as well as after it, e.g.:
- # 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:
For string conversions, specifying a precision truncates the string to fit in the specified width:
You can also get the precision from the next argument using
You cannot currently get the precision from a specified number,
but it is intended that this will be possible in the future 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
. For integer
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 produce errors if Perl does not understand "quads" in your installation. (This requires that either the platform natively supports quads or Perl was 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
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 the case that long doubles and doubles are the same thing:
The size specifier
has no effect for Perl code, but it is 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.
Normally, sprintf takes the next unused argument as the value to
format for each format specification. If the format specification
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, $c;
for the width,
for the precision and
as the value to format, while:
- print '<%*1$.*s>', $a, $b;
for the width and the precision, and
value to format.
Here are some more examples - beware that when using an explicit
may need to be escaped: