PRINTF(1)                  OpenBSD Reference Manual                  PRINTF(1)

NAME
     printf - formatted output

SYNOPSIS
     printf format [arguments ...]

DESCRIPTION
     printf formats and prints its arguments, after the first, under control
     of the format. The format is a character string which contains three
     types of objects: plain characters, which are simply copied to standard
     output, character escape sequences which are converted and copied to the
     standard output, and format specifications, each of which causes printing
     of the next successive argument.

     The arguments after the first are treated as strings if the corresponding
     format is b, c or s; otherwise it is evaluated as a C constant, with the
     following extensions:

           o   A leading plus or minus sign is allowed.

           o   If the leading character is a single or double quote, the value
               is the ASCII code of the next character.

     The format string is reused as often as necessary to satisfy the
     arguments. Any extra format specifications are evaluated with zero or the
     null string.

     Character escape sequences are in backslash notation as defined in ANSI
     X3.159-1989 (``ANSI C''). The characters and their meanings are as fol-
     lows:

           \e      Write an <escape> character.
           \a      Write a <bell> character.
           \b      Write a <backspace> character.
           \f      Write a <form-feed> character.
           \n      Write a <new-line> character.
           \r      Write a <carriage return> character.
           \t      Write a <tab> character.
           \v      Write a <vertical tab> character.
           \'      Write a <single quote> character.
           \\      Write a backslash character.
           \num    Write an 8-bit character whose ASCII value is the 1-, 2-,
                   or 3-digit octal number num.

     Each format specification is introduced by the percent (`%') character.
     The remainder of the format specifiers include, in the following order:

     Zero or more of the following flags:

             #       Specifies that the value should be printed in an
                     ``alternate form''. For the c, d, and s formats, this op-
                     tion has no effect.  For the o format the precision of
                     the number is increased to force the first character of
                     the output string to a zero.  For the x (X) format, a
                     non-zero result has the string 0x (0X) prepended to it.
                     For e, E, f, g, and G formats, the result will always
                     contain a decimal point, even if no digits follow the
                     point (normally, a decimal point only appears in the re-
                     sults of those formats if a digit follows the decimal
                     point).  For g and G formats, trailing zeros are not re-
                     moved from the result as they would otherwise be.

             -       Specifies the left adjustment of the output in the indi-

                     cated field.

             +       Specifies that there should always be a sign placed be-
                     fore the number when using signed formats.

             ` '     A space specifies that a blank should be left before a
                     positive number for a signed format.  A `+' overrides a
                     space if both are used.

             0       A zero character specifies that zero-padding should be
                     used rather than blank-padding.  This flag is ignored if
                     used with a precision specifier and any of the d, i, o,
                     u, or x (X) formats.  A `-' overrides a `0' if both are
                     used.

     Field Width:
             An optional digit string specifying a field width; if the output
             string has fewer characters than the field width it will be
             blank-padded on the left (or right, if the left-adjustment indi-
             cator has been given) to make up the field width (note that a
             leading zero is a flag, but an embedded zero is part of a field
             width).

     Precision:
             An optional period (`.'), followed by an optional digit string
             giving a precision which specifies the number of digits to appear
             after the decimal point, for e and f formats, or the maximum num-
             ber of characters to be printed from a string; if the digit
             string is missing, the precision is treated as zero.

     Format:
             A character which indicates the type of format to use (one of
             diouxXfEgGbcs).

     A field width or precision may be `*' instead of a digit string.  In this
     case an argument supplies the field width or precision.

     The format characters and their meanings are:

     diouXx      The argument is printed as a signed decimal (d or i), un-
                 signed octal, unsigned decimal, or unsigned hexadecimal (x or
                 X), respectively.

     f           The argument is printed in the style [-]ddd.ddd where the
                 number of d's after the decimal point is equal to the preci-
                 sion specification for the argument.  If the precision is
                 missing, 6 digits are given; if the precision is explicitly
                 0, no digits and no decimal point are printed.

     eE          The argument is printed in the style [-]d.ddde+-dd where
                 there is one digit before the decimal point and the number
                 after is equal to the precision specification for the argu-
                 ment; when the precision is missing, 6 digits are produced.
                 An upper-case `E' is used for an E format.

     gG          The argument is printed in style f or in style e (E) whichev-
                 er gives full precision in minimum space.

     b           Characters from the string argument are printed with back-
                 slash-escape sequences expanded.

     c           The first character of argument is printed.

     s           Characters from the string argument are printed until the end
                 is reached or until the number of characters indicated by the
                 precision specification is reached; however if the precision
                 is 0 or missing, all characters in the string are printed.

     %           Print a `%'; no argument is used.

     In no case does a non-existent or small field width cause truncation of a
     field; padding takes place only if the specified field width exceeds the
     actual width.

     The printf utility exits 0 on success or 1 on failure.

EXAMPLES
     Convert a hexidecimal value to decimal and print it out:

           printf "%d\n" 0x20

     Print the decimal representation of the character 'a' (see ascii(7)):

           printf "%d\n" \'a

SEE ALSO
     echo(1), printf(3)

STANDARDS
     The printf utility conforms to IEEE Std1003.2-1992 (``POSIX.2'').

HISTORY
     The printf command appeared in 4.3BSD-Reno.

CAVEATS
     It is important never to pass a string with user-supplied data as a for-
     mat without using `%s'. An attacker can put format specifiers in the
     string to mangle your stack, leading to a possible security hole.

     Always be sure to use the proper secure idiom:

           printf "%s" "$STRING"

BUGS
     Since arguments are translated from ASCII to floating-point, and then
     back again, floating-point precision may be lost.

OpenBSD 2.9                    November 5, 1993                              3
