Bash: printf

$ printf
printf: usage: printf [-v var] format [arguments]

Also see: https://linuxize.com/post/bash-printf-command/

Format Placeholder Syntax

%[flags][width][.precision]specifier

Flags

Some commonly used:

-Left align the printed text within the field. (default: right-aligned)
+Prefix the numbers with a + or - signs. (default: no + for positive number).
Negative number is always is prefixed with -.
0Pads numbers with leading zeros rather than space.

Also see: https://www.gnu.org/software/libc/manual/html_node/Integer-Conversions.html#Integer-Conversions

Specifiers

Some commonly used:

%sstring
%d, %iinteger
%uunsigned decimal integer
%f floating point
%efloating-point number in exponential notation (lower-case)
%Efloating-point number in exponential notation (upper-case)
%cchar (single character)
%ooctal integer
%xunsigned hexadecimal integer (lower-case)
%Xunsigned hexadecimal integer (upper-case)
%bstring with backslash escape character
%qshell-quoted, reusable as input
%%percent sign

Examples

$ printf "Hello World! \n"
Hello World!

$ printf "Hello %s! \n" World
Hello World!

$ printf "%s's age is %d. \n" "John Doe" 131
John Doe's age is 131.

printf "Pad up to 4 spaces:%4d" 1
Pad up to 4 spaces:   1

$ printf "Pad up to 4 spaces:%4d" 1111
Pad up to 4 spaces:1111

$ printf "Pad up to 4 zeros:%04d\n" 0
Pad up to 4 zeros:0000

$ printf "Pad up to 4 zeros:%04d\n" 1
Pad up to 4 zeros:0001

$ printf "Cost $%.2f" 3.333333
Cost $3.33
$ info printf

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.  *Note ‘printf’ format
directives: (libc)Output Conversion Syntax, 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 further5’
     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 hostsn
     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’.  *Note 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:ept
‘\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 theted
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’.  *Note 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 invokedr
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.

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