15.2 printf: Format and print data

printf does formatted printing of text. Synopsis:

printf format [argument]…

printf prints the format string, interpreting ‘%’ directives and ‘\’ escapes to format numeric and string arguments in a way that is mostly similar to the C ‘printf’ function. See printf format directives in The GNU C Library Reference Manual, for details. The differences are listed below.

Due to shell aliases and built-in printf functions, using an unadorned printf interactively or in a script may get you different functionality than that described here. Invoke it via env (i.e., env printf …) to avoid interference from the shell.

  • The format argument is reused as necessary to convert all the given arguments. For example, the command ‘printf %s a b’ outputs ‘ab’.
  • Missing arguments are treated as null strings or as zeros, depending on whether the context expects a string or a number. For example, the command ‘printf %sx%d’ prints ‘x0’.
  • An additional escape, ‘\c’, causes printf to produce no further output. For example, the command ‘printf 'A%sC\cD%sF' B E’ prints ‘ABC’.
  • The hexadecimal escape sequence ‘\xhh’ has at most two digits, as opposed to C where it can have an unlimited number of digits. For example, the command ‘printf '\x07e'’ prints two bytes, whereas the C statement ‘printf ("\x07e")’ prints just one.
  • An additional directive ‘%b’, prints its argument string with ‘\’ escapes interpreted in the same way as in the format string, except that octal escapes are of the form ‘\0ooo’ where ooo is 0 to 3 octal digits. If ‘\ooo’ is nine-bit value, ignore the ninth bit. If a precision is also given, it limits the number of bytes printed from the converted string.
  • An additional directive ‘%q’, prints its argument string in a format that can be reused as input by most shells. Non-printable characters are escaped with the POSIX proposed ‘$’ syntax, and shell metacharacters are quoted appropriately. This is an equivalent format to ls --quoting=shell-escape output.
  • Numeric arguments must be single C constants, possibly with leading ‘+’ or ‘-’. For example, ‘printf %.4d -3’ outputs ‘-0003’.
  • If the leading character of a numeric argument is ‘"’ or ‘'’ then its value is the numeric value of the immediately following character. Any remaining characters are silently ignored if the POSIXLY_CORRECT environment variable is set; otherwise, a warning is printed. For example, ‘printf "%d" "'a"’ outputs ‘97’ on hosts that use the ASCII character set, since ‘a’ has the numeric value 97 in ASCII.

A floating point argument is interpreted according to the LC_NUMERIC category of either the current or the C locale, and is printed according to the current locale. For example, in a locale whose decimal point character is a comma, the command ‘printf '%g %g' 2,5 2.5’ outputs ‘2,5 2,5’. See Floating point.

printf interprets ‘\ooo’ in format as an octal number (if ooo is 1 to 3 octal digits) specifying a byte to print, and ‘\xhh’ as a hexadecimal number (if hh is 1 to 2 hex digits) specifying a character to print. Note however that when ‘\ooo’ specifies a number larger than 255, printf ignores the ninth bit. For example, ‘printf '\400'’ is equivalent to ‘printf '\0'’.

printf interprets two character syntaxes introduced in ISO C 99: ‘\u’ for 16-bit Unicode (ISO/IEC 10646) characters, specified as four hexadecimal digits hhhh, and ‘\U’ for 32-bit Unicode characters, specified as eight hexadecimal digits hhhhhhhh. printf outputs the Unicode characters according to the LC_CTYPE locale. Unicode characters in the ranges U+0000…U+009F, U+D800…U+DFFF cannot be specified by this syntax, except for U+0024 ($), U+0040 (@), and U+0060 ()`.

The processing of ‘\u’ and ‘\U’ requires a full-featured iconv facility. It is activated on systems with glibc 2.2 (or newer), or when libiconv is installed prior to this package. Otherwise ‘\u’ and ‘\U’ will print as-is.

The only options are a lone --help or --version. See Common options. Options must precede operands.

The Unicode character syntaxes are useful for writing strings in a locale independent way. For example, a string containing the Euro currency symbol

$ env printf '\u20AC 14.95'

will be output correctly in all locales supporting the Euro symbol (ISO-8859-15, UTF-8, and others). Similarly, a Chinese string

$ env printf '\u4e2d\u6587'

will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).

Note that in these examples, the printf command has been invoked via env to ensure that we run the program found via your shell’s search path, and not a shell alias or a built-in function.

For larger strings, you don’t need to look up the hexadecimal code values of each character one by one. ASCII characters mixed with \u escape sequences is also known as the JAVA source file encoding. You can use GNU recode 3.5c (or newer) to convert strings to this encoding. Here is how to convert a piece of text into a shell script which will output this text in a locale-independent way:

$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
    '\u4e2d\u6587\n' > sample.txt
$ recode BIG5..JAVA < sample.txt \
    | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
    > sample.sh

An exit status of zero indicates success, and a nonzero value indicates failure.