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printf
printf format
printf "format string" variable
The use of printf is the same as in C language, and does not require parentheses and commas to separate:
printf "%-10s %-5d\n" hello_world
Print result:
hello_world
When printing a string, if there are spaces or special symbols in the string, it needs to be enclosed in double quotes:
printf "%-10s %-5d\n" "hello world"
Print result:
hello world
Common escape characters
| escape character | illustrate |
|---|---|
| \n | line break |
| \t | horizontal tab |
| \v | vertical tab |
| \a | warning character |
| \b | backspace |
| \f | Feed character |
| \r | carriage return |
| ? | Used when writing multiple question marks in succession |
| ’ | used to represent the character ' |
| " | Used to represent the character " |
| \\ | Used to represent the character \ |
| \ddd | Octal number printing, where ddd means printing a 1~3 octal number |
| \xdd | Hexadecimal number printing, where dd means 1~2 hexadecimal numbers |
echo
Unlike printf, echo will automatically wrap each time it prints
echo print format
echo [Options can be added] [Print content]
| options | illustrate |
|---|---|
| -n | Disable word wrap |
| -e | Allow printing with escape characters |
| -E | Disallow \escaping characters with |
1) -n option
[wjj@learning study]$ echo -n Hello World！
Hello World！[wjj@learning study]$
Because the automatic line feed function is canceled, the printed result is on the same line as the next command.
2) -e option
[wjj@learning study]$ echo -e "zhangsan\nlisi\nwangwu"
zhangsan
lisi
wangwu
The -e option allows echo to print using the above escape symbols.
3) -E option
[wjj@learning study]$ echo -E "zhangsan\nlisi\nwangwu"
zhangsan\nlisi\nwangwu
The -E option cancels \the escape function.
Three ways of echo printing
1) Print without quotes
Format:echo 字符串
echo hello world
2) Print the contents of the double quotes
Format:echo "字符串"
echo "hello world"
3) Print the content in single quotes
Formatecho ‘字符串’
echo 'hello world'
The difference between the three printing methods
- The unquoted way cannot be printed
;because;in the shell as a command delimiter - The way of double quotes supports parsing special characters. If you don’t want to parse special characters, you need to add escape characters
\ - The way of single quotes does not support all special symbols, what you see is what you get
Escape characters supported by echo
Most of the escape characters supported by echo are the same as those of the printf function, and some of them are different, which need to be compared with the previous table.
| escape character | illustrate | Remarks (whether it is the same as the printf function) |
|---|---|---|
| \a | warning character | √ |
| \b | backspace | √ |
| \c | Suppress printing characters (do not print characters after \c) | × |
| \e | Escape characters (see color printing below for examples) | × |
| \f | Near paper character (newline end alignment) | √ |
| \n | line break | √ |
| \r | carriage return | √ |
| \t | horizontal tab | √ |
| \v | vertical tab | √ |
| \\ | character'\' | √ |
| \0ddd | Octal number printing, where ddd means printing a 1~3 octal number (slightly different from printf) | × |
| \xdd | Hexadecimal number printing, where dd means 1~2 hexadecimal numbers | √ |
About printing exclamation point (!)
As a special symbol in the shell
!, you need to pay attention to the following issues when printing it
1) printf and echo pair !escape printing
[wjj@learning ~]$ printf "Hello World\!\n"
Hello World\!
[wjj@learning ~]$ echo "Hello World\!"
Hello World\!
After !escaping and printing, the printing will not report an error, but the printing will appear \. This situation will only appear when the command is entered on the command line. Using the script to print can !normally escape.
2) printf formatted output
[wjj@learning ~]$ printf "%-s %-s %c\n" Hello World !
Hello World !
By formatting the output, !print it as a variable, and the print result is correct.
3) echo prints without quotes
[wjj@learning ~]$ echo Hello World !
Hello World !
echo can correctly output the result without quotes, but this method is not conducive to scripting, so it is not recommended.
4) ‘’print with echo
[wjj@learning ~]$ echo 'Hello World!'
Hello World!
Because the single quotation mark method does not support all special symbols, what you see is what you get, so it can be printed normally, and this method is recommended
color output
General format:echo -e "\e[am 文本 \e[am"
Where a is the corresponding color ASCII code value, used to control 文本颜色, 背景颜色and 文本样式.
文本颜色mainly include:reset=0, black=30, red=31, green=32, yellow=33, blue=34, magenta=35, cyan=36, white=37
背景颜色mainly include:reset=0, black=40, red=41, green=42, yellow=43, blue=44, magenta=45, cyan=46, white=47
文本样式mainly include:reset 0, set highlight=1, underline=4, blink=5, reverse=7, blank=8,
Example 1: print red font:
echo -e "\e[31m red text \e[0m"
in:
- "\e[31m \e[0m" is the standard format
- \e[31m is an escape character, 31 corresponds to the red color of the text
- \e[0m is to reset the text, if not reset, it will keep the format
The effect is as follows:
Example 2: print red font, yellow background
echo -e "\e[43;31m red text \e[0m"
in:
- 43;31m corresponds to the background color yellow and the font color black respectively, the order of the two is not fixed, and the final system operates according to the value corresponding to the ASCII code.
The effect is as follows:
Example 3: print red font, yellow background, underlined
echo -e "\e[4;43;31m red text \e[0m"
- By continuously adding control options, the text display is more beautiful
The effect is as follows:
