BASH printf Notes

Cheat sheet for printf in bash

printf doesn't assume newlines, so add \n to create one.

Common Formats

Specifier Meaning Example
%s String printf "%s\n" "text"
%d Integer printf "%d\n" 50
%f Float printf "%f\n" 2.71828
%e Float in scientific notation (lower) printf "%e\n" 2.71828
%E Float in scientific notation (upper) printf "%E\n" 2.71828
%g Float (trim) in scientific notation (lower) printf "%g\n" 2.71828
%G Float (trim) in scientific notation (upper) printf "%G\n" 2.71828
%x Hex (lower) printf "%x\n" 255
%X Hex (upper) printf "%X\n" 255
%o Octal printf "%o\n" 8
%b Interpret backslash escapes printf "%b" "one\ntwo\three\n
%% Interpret backslash escapes printf "%s%%\n" "1"

Common Backslash Escapes

Escape Meaning
\n Newline
\t Tab
\v Vertical tab
\\ Backslash
\" Double quote
\r Carriage return
\f Form feed

Field Width and Alignment

Specifier Meaning Example
%10s right align in 10 spaces " apple"
%-10s left align in 10 spaces "apple "

Number Padding

Add a 0 before the width number:


printf "%05d\n" 50
00050

Precision for Strings and Floats

For strings, .N limits the number of characters printed:


printf "%.3s\n" "banana"
ban

For floats, .N sets the number of digits after the decimal point (notice that rounding is automatic):


printf "%.2f\n" 2.71828
2.72

Works for scientific notation, too:


printf "%.3e\n" 2.71828
2.718e+00

Dynamic Width and Precision

Use the asterisk with this syntax: %*s\n 10 "apple":


printf "%*s\n" 10 "apple"
     apple

Note: Width is about field size. Thus, in the above example, the 10 adds five empty fields before the string apple, since the string apple has five fields, totaling ten.

Hex and Octal Specifics

Use the # flag to add 0 as the leading digit.

Octal examples:


printf "%o\n" 30
36
printf "%#o\n" 30
036

Hex lower examples:


printf "%x\n" 30
1e
printf "%#x\n" 30
0x1e

Hex upper examples:


printf "%X\n" 30
1E
printf "%#X\n" 30
0X1E

Cases

Count in hexadecimal:


for i in {1..20} ; do
	printf "%X\n" "$i"
done