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The printf command

This command lets you print the value of a variable by formatting it using rules. It is pretty similar to the printf in C language.

Syntax:

$printf [-v variable_name] format [arguments]

Options:

OPTION Description
FORMAT FORMAT controls the output, and defines the way that the ARGUMENTs will be expressed in the output
ARGUMENT An ARGUMENT will be inserted into the formatted output according to the definition of FORMAT
--help Display help and exit
--version Output version information adn exit

Formats:

The anatomy of the FORMAT string can be extracted into three different parts,

  • ordinary characters, which are copied exactly the same characters as were used originally to the output.
  • interpreted character sequences, which are escaped with a backslash ("\").
  • conversion specifications, this one will define the way the ARGUMENTs will be expressed as part of the output.

You can see those parts in this example,

printf " %s is where over %d million developers shape \"the future of sofware.\" " Github 65

The output:

Github is where over 65 million developers shape "the future of sofware."

There are two conversion specifications %s and %d, and there are two escaped characters which are the opening and closing double-quotes wrapping the words of the future of software. Other than that are the ordinary characters.

Conversion Specifications:

Each conversion specification begins with a % and ends with a conversion character. Between the % and the conversion character there may be, in order:
- A minus sign. This tells printf to left-adjust the conversion of the argument
number An integer that specifies field width; printf prints a conversion of ARGUMENT in a field at least number characters wide. If necessary it will be padded on the left (or right, if left-adjustment is called for) to make up the field width
. A period, which separates the field width from the precision
number An integer, the precision, which specifies the maximum number of characters to be printed from a string, or the number of digits after the decimal point of a floating-point value, or the minimum number of digits for an integer
h or l These differentiate between a short and a long integer, respectively, and are generally only needed for computer programming

The conversion characters tell printf what kind of argument to print out, are as follows:

Conversion char Argument type
s A string
c An integer, expressed as a character corresponds ASCII code
d, i An integer as a decimal number
o An integer as an unsigned octal number
x, X An integer as an unsigned hexadecimal number
u An integer as an unsigned decimal number
f A floating-point number with a default precision of 6
e, E A floating-point number in scientific notation
p A memory address pointer
% No conversion

Here is the list of some examples of the printf output the ARGUMENT. we can put any word but in this one we put a 'linuxcommand` word and enclosed it with quotes so we can see easier the position related to the whitespaces.

FORMAT string ARGUMENT string Output string
"%s" "linuxcommand" "linuxcommand"
"%5s" "linuxcommand" "linuxcommand"
"%.5s" "linuxcommand" "linux"
"%-8s" "linuxcommand" "linuxcommand"
"%-15s" "linuxcommand" "linuxcommand "
"%12.5s" "linuxcommand" " linux"
"%-12.5" "linuxcommand" "linux "
"%-12.4" "linuxcommand" "linu "

Notes:

  • printf requires the number of conversion strings to match the number of ARGUMENTs
  • printf maps the conversion strings one-to-one, and expects to find exactly one ARGUMENT for each conversion string
  • Conversion strings are always interpreted from left to right.

Here's the example:

The input

printf "We know %f is %s %d" 12.07 "larger than" 12

The output:

We know 12.070000 is larger than 12

The example above shows 3 arguments, 12.07, larger than, and 12. Each of them interpreted from left to right one-to-one with the given 3 conversion strings (%f, %d, %s).

Character sequences which are interpreted as special characters by printf:

Escaped char Description
\a issues an alert (plays a bell). Usually ASCII BEL characters
\b prints a backspace
\c instructs printf to produce no further output
\e prints an escape character (ASCII code 27)
\f prints a form feed
\n prints a newline
\r prints a carriage return
\t prints a horizontal tab
\v prints a vertical tab
\" prints a double-quote (")
\\ prints a backslash ()
\NNN prints a byte with octal value NNN (1 to 3 digits)
\xHH prints a byte with hexadecimal value HH (1 to 2 digits)
\uHHHH prints the unicode character with hexadecimal value HHHH (4 digits)
\UHHHHHHHH prints the unicode character with hexadecimal value HHHHHHHH (8 digits)
%b prints ARGUMENT as a string with "\" escapes interpreted as listed above, with the exception that octal escapes take the form \0 or \0NN

Examples:

The format specifiers usually used with printf are stated in the examples below:

  • %s
$printf "%s\n" "Printf command documentation!"

This will print Printf command documentation! in the shell.

Other important attributes of printf command:

  • %b - Prints arguments by expanding backslash escape sequences.
  • %q - Prints arguments in a shell-quoted format which is reusable as input.
  • %d , %i - Prints arguments in the format of signed decimal integers.
  • %u - Prints arguments in the format of unsigned decimal integers.
  • %o - Prints arguments in the format of unsigned octal(base 8) integers.
  • %x, %X - Prints arguments in the format of unsigned hexadecimal(base 16) integers. %x prints lower-case letters and %X prints upper-case letters.
  • %e, %E - Prints arguments in the format of floating-point numbers in exponential notation. %e prints lower-case letters and %E prints upper-case.
  • %a, %A - Prints arguments in the format of floating-point numbers in hexadecimal(base 16) fractional notation. %a prints lower-case letters and %A prints upper-case.
  • %g, %G - Prints arguments in the format of floating-point numbers in normal or exponential notation, whichever is more appropriate for the given value and precision. %g prints lower-case letters and %G prints upper-case.
  • %c - Prints arguments as single characters.
  • %f - Prints arguments as floating-point numbers.
  • %s - Prints arguments as strings.
  • %% - Prints a "%" symbol.

More Examples:

The input:

printf 'Hello\nyoung\nman!'

The output:

hello 
young
man!

The two \n break the sentence into 3 parts of words.

The input:

printf "%f\n" 2.5 5.75

The output

2.500000
5.750000

The %f specifier combined with the \n interpreted the two arguments in the form of floating point in the seperated new lines.