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:
printfrequires the number of conversion strings to match the number of ARGUMENTsprintfmaps 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.