Shell printf Command

in the previous section we learned about the Shell's echo command, which we'll learn from the Shell's other output command printf.

The printf command mimics the printf () program in the C library.

Standard, so scripting with printf is better than using echo portability.

printf uses reference text or space-delimited parameters, which can be used outside of the format string in printf, as well as the width of the string, left and right alignment, and so on. Default printf does not automatically add line breaks like echo, we can add \ n manually.

The syntax of the printf command:

printf  format-string  [arguments ...]

parameter Description: format-string: for the format control string arguments: is the parameter list.

Examples are as follows:

$ echo "Hello, Shell"
Hello, Shell
$ printf "Hello, shell\n"
Hello, Shell
$

Next, I'll use a script to demonstrate the power of printf:

#!/bin/bash
# Author: Rookie Tutorial
# url:www.runoob.com
 
printf "%-10s%-8s%-4s\n" name sex weight kg  
printf "%-10s%-8s% -4.2f\n "Guo Jing male 66.1234 
printf"%-10s%-8s%-4.2f\n "Yang over male 48.6543 

Execute the script with the output as follows:

Name     gender   weight kg
guo Jing     male      66.12
yang over     male      48.65
Guoff     female      47.99

%s%c%d%f are format alternates

%-10s refers to a width of 10 characters (-for left alignment, not to right-aligned), any character will be displayed in 10 character justifies characters, if not enough is automatically filled with spaces, more than will also show the content.

%-4.2F refers to the format of decimals, where. 2 refers to 2 decimal places reserved.

More examples:

#!/bin/bash
# Author: Rookie Tutorial
# url:www.runoob.com
 
# format-string for double quotes
printf "%d%s\n" 1 "abc"

# Single quote with double quote effect 
printf '%d%s\n ' 1 "abc" 

# no quotation marks can also output
printf%s abcdef

# format only one parameter is specified, but the extra parameters are still output in that format. Format-string is reused
printf%s abc def

printf "%s\n" abc def

printf "%s%s%s\n" a b c D e F g h i j

# if not With arguments, then%s is replaced with NULL,%d replaces with 0

Execute the script with the output as follows:

1 ABC
1 ABC
ABCDEFABCDEFABC
def
a b c
d E F
g H i
J and  
 0

escape sequences for printf

sequence	Description
\a	A warning character, usually an ASCII bel character
\b	Back off
\c	Suppresses (does not display) the newline character at any end of the output (only valid in the parameter string under the control of the%b format designator), and any characters left in the argument, any subsequent arguments, and any characters left in the format string are ignored
\f	Page Change (formfeed)
\ n	Line break
\ r	Enter (carriage return)
\ t	Horizontal tab
\v	Vertical tab
\\	A literal backslash character
\ddd	A character that represents an octal value of 1 to 3 digits. Valid only in format strings
\0ddd	Represents octal value characters from 1 to 3 bits

Example

$ printf "A string, no processing:<%s>\n" "A\NB" a string, no processing:<a\nb> $ printf "a string, no proce                  ssing:<%b>\n "" A\nb "A string, no processing:<a b> $ printf" www.runoob.com \a "www.runoob.com $ #不换行