Chapter II ${of Shell string processing}

The previous section explains why referencing variables with ${}, ${} also has an important function, that is, text processing, a single line of text can basically meet all your needs.

3.1 Get string length

# var= ' Hello world! ' # echo $VARhello world!# echo ${#VAR}12

3.2 String slices

Intercept the Hello string: # var= ' Hello world! ' # echo ${var:0:5}hello Intercept World string: # echo ${var:5:-1}world Intercept last character: # echo ${var: (-1)}!

3.3 Replacement string

# var= ' Hello World world! ' Replace the first world string with world:# echo ${var/world/world}hello World world! Replace all world strings with world:# Echo ${var//world/world}hello World world!

3.4 String interception

# url= "to intercept the right string with a//delimiter: # echo ${url#*//} www.baidu.com/baike/user.html the right string with/for the delimiter: # echo ${url##*/}user.html to// The delimiter intercepts the left string: # Echo ${url%%//*} http: intercepts the left string with the/delimiter: # echo ${url%/*}http://www.baidu.com/baike to the left: # echo ${url%.* }http://www.baidu.com/baike/user to. The right side of the delimiter: # echo ${url##*.} Html

# Remove the left, match the first one from the left, # #从右边匹配第一个.

% remove right, match first from right, percent to match first from left.

This is the case with the * number.

3.5 Variable Status Assignment

${var:-string} returns a string if the VAR variable is empty

${var:+string} returns a string if the VAR variable is not empty

${var:=string} if the var variable is empty then re-assign the value of the var variable to string

${var:?string} outputs a string to stderr if the VAR variable is empty

Returns Hello world!:# var=# echo ${var:-' Hello world! '} If the variable is empty Hello world! If the variable is not empty return hello world!:# var= "Hello" [[email protected] ~]# echo ${var:+ ' Hello world! '} Hello world! If the variable is empty, re-assign the value: # var=# echo ${var:=hello}hello# echo $VARhello If the variable is empty the information output stderr:# var=# echo ${var:?value is Nu LL}-bash:var:value is null

${} The main purpose is probably so much, you can also get the array elements, in the following chapters.

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Then we introduce the string output color, sometimes the key place needs to be bold, the color is the best way:

30: Black 31: Red 32: Green 33: Yellow 34: Blue 35: Purple 36: Dark green 37: white	40: Black 41: Crimson 42: Green 43: yellow 44: Blue 45: Purple 46: Dark green 47: White	0: terminal default settings 1: Highlight 4: underline 5: blinking 7: Anti-white display 8: hidden
Format: \033[1;31;40m # 1 is the display mode, optional. 31 is the font color. 40m is the font background color. \033[0M # Restores the terminal default color, that is, cancels the color setting.

Example:

#!/bin/bash# font color for i in {31..37}; Do echo-e "\033[$i; 40mHello world!\033[0m" done# background color for i in {41..47}; do echo-e "\033[47;${i}mhello world!\033[0m "done# display mode for i in {1..8}; Do echo-e "\033[$i, 31;40mhello world!\033[0m" done

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Chapter II ${of Shell string processing}