Shell printf command

The last chapter we learned Shell echo command, in this chapter we learn another output Shell command printf.

printf command imitate C library (library) in the printf () procedure.

Standard definition, so use printf script better than using echo portability.

printf using a reference text or parameters separated by spaces, can be used outside of the printf format string, you can also develop the width of the string, and so on left and right alignment. Default printf does not automatically add a line break like echo, we can add \ n manually.

printf command syntax:

printf  format-string  [arguments...]

Parameter Description:

• format-string: format control string
• arguments: the list of parameters.

Examples are as follows:

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

Next, I use a script to reflect the powerful printf:

#!/bin/bash
# author:本教程
# url:www.w3big.com
 
printf "%-10s %-8s %-4s\n" 姓名 性别 体重kg  
printf "%-10s %-8s %-4.2f\n" 郭靖 男 66.1234 
printf "%-10s %-8s %-4.2f\n" 杨过 男 48.6543 
printf "%-10s %-8s %-4.2f\n" 郭芙 女 47.9876 

Execute the script, the output is as follows:

姓名     性别   体重kg
郭靖     男      66.12
杨过     男      48.65
郭芙     女      47.99

% S% c% d% f format are placeholders

% -10s Refer to a width of 10 characters (- for left-aligned, right-aligned, said no), any characters are displayed in 10 characters wide characters, if insufficient space is automatically filled in, it will be more than content show all of them.

% -4.2f Refers to decimal format, which means .2 2 decimal places.

More examples:

#!/bin/bash
# author:本教程
# url:www.w3big.com
 
# format-string为双引号
printf "%d %s\n" 1 "abc"

# 单引号与双引号效果一样 
printf '%d %s\n' 1 "abc" 

# 没有引号也可以输出
printf %s abcdef

# 格式只指定了一个参数，但多出的参数仍然会按照该格式输出，format-string 被重用
printf %s abc def

printf "%s\n" abc def

printf "%s %s %s\n" a b c d e f g h i j

# 如果没有 arguments，那么 %s 用NULL代替，%d 用 0 代替
printf "%s and %d \n" 

Execute the script, the output is as follows:

1 abc
1 abc
abcdefabcdefabc
def
a b c
d e f
g h i
j  
 and 0

Printf's escape sequence

Examples

$ printf "a string, no processing:<%s>\n" "A\nB"
a string, no processing:<A\nB>

$ printf "a string, no processing:<%b>\n" "A\nB"
a string, no processing:<A
B>

$ printf "www.w3big.com \a"
www.w3big.com $                  #不换行