A summary of several cold knowledge of the shell (IFS, arrays, replacements, cuts, lookups)

IFS:

The use of IFS directly to explain what the specific ifs is doing ... Own Google

First create a file of "a", and "a":

Then we look at the LS:

--> ls
a A a  

That is true.

And then if we need to write a script to manipulate each file:

--> for I in $ (LS); Do echo "$i";d one a A a

But it turned out to be so, obviously inconsistent with our requirements.

Because the IFS value is a space, a tab character, a carriage return. So this turns a A to 2 a.

But we modified the IFS as follows:

--> oldifs= $IFS ifs=$ ' \ n '; For i in $ (LS); Do echo "$i";d one; ifs= $OldIfs
a
a

Well, that's what we're going to do, this time with the ' \ n ' as a separator.

Arrays:

A script is described:

#!/bin/bash # *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* # > Author:xiaojunyu/lunaw # > Mail:xiaoj Unyu5201314@163.com # > Gmail:lunaw.org@gmail.com # > Blog:http://blog.csdn.net/lunaw # > Web:http: lunaw.org http://lunaw.net # *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* # depends:=+libsqlite3 +libcurl +libpthread +LIBC # Default selected Package selectpackages= ("sed" "gawk" "grep" "BC" "Luci-lib-json" "Iperf" "TC" "Restorefactory" "xinetd") 
"N2N") # The default package priority is stronger than the selected package unselectpackages= ("Horst" "Vim-full" "Vim-runtime" "qos-scripts" "WiFiDog" "Libcurl" "Curl" "TC" "Sqlite3-cli" "Libsqlite3") if [[F. config]]; Then for Name in ' seq 1 ${#SelectPackages [*]} ' do packagename= ' config_package_${selectpackages[$ (expr $Nam e-1)]} ' if [[' Cat config| grep ' ${packagename}=y ' | wc-l ' = 0]]; Then Echo-e "\e[01;31mnot Found (${packagename}=y)" If [[' Cat]. config| grep "# ${packagename} is not set" | Wc-l ' = = 1]];  Then Echo-e ' \e[01;33mfound (# ${packagename} is not set) ' Sed-i ' s/# ${packagename} is
            Not set/${packagename}=y/g ". config echo-e" \e[01;36mreplace (${packagename}=y) done! " else Echo-e "\e[01;31mnot Found (# ${packagename} is not set)" echo "${packagename}=y" &
            gt;>. config echo-e "\e[01;36madd (${packagename}=y) done!" Fi else Echo-e "\e[01;33mfound (${packagename}=y)" Fi done Echo "------------------- -------------------"for Name in" SEQ 1 ${#UnSelectPackages [*]} ' do packagename= ' config_package_${unselect packages[$ (expr $Name-1)]} "if [[' Cat. config| grep" # ${packagename} is not set "| wc-l ' = = 0]]"; Then Echo-e "\e[01;31mnot Found (# ${packagename} is not set)" If [[' Cat. config| grep "${packagename}=y" | Wc-l ' = = 1]]; Then Echo-e "\e[01;33mfound (${packagename}=y) "Sed-i" s/${packagename}=y/# ${packagename} is not set/g. config
            Echo-e "\e[01;36mreplace (# ${packagename} is not set) done!" else Echo-e "\e[01;31mnot Found (${packagename}=y)" echo "# ${packagename} is not set" &
            gt;>. config echo-e "\e[01;36madd (# ${packagename} is not set) done!" Fi else Echo-e "\e[01;33mfound (# ${packagename} is not set)" fi do Else Echo-e "  \e[01;31mnot Found. config "fi echo-e" \e[01;00m+---------------------------------+ "ECHO-E" \e[01;00m|  Don't worry, it's just a couple of bags to choose from! | "Echo-e" \e[01;00m+---------------------------------+ "Sleep 1

Replace:

Single substitution

--> xiaoname= "Xiaojunyu"; echo "${xiaoname/x/j}"
Jiaojunyu

Replace All

--> xiaoname= "Xiaojunyu"; echo "${xiaoname//u/a}"
Xiaojanya

Delete

--> xiaoname= "Xiaojunyu"; echo "${xiaoname//u/}"
Xiaojny

Cutting:

There are several methods, the first of which are:

Xiaoch= "Xiao;jun;yu" for                                                                                                                     
i in ${xiaoch//;/}                                                                                                                  
Do                                                                                                                                       
    echo "$i"                                                                                                                            

Output:

Xiao
June
Yu

But if that's the case:

Xiaoch= "Xiao;j Un;yu" for                                                                                                                    
i in ${xiaoch//;/}                                                                                                                  
Do                                                                                                                                       
    echo "$i"                                                                                                                            

Output:

Xiao
J
un
yu

It's not what we expected, and then the second method of segmentation

Ifs method:

Xiaoch= "Xiao;j Un;yu"                                                                                                                            
oldifs= $IFS                                                                                                                               
ifs=$ '; '                                                                                                                        
                                                             Xiaoarr= ($XIAOCH)                                                                                                                   
For i in ${xiaoarr[@]}                                                                                                                                       
    Todo                          echo "$i"                                                                                                   
Done ifs= $OldIFS

Output:

Xiao
j un
yu

Find:

Find out if a string contains another string

--> xiaoa= "ABC"; Xiaob= "a"; [["${xiaoa/${xiaob}/}" = = "$XiaoA"]] && echo "No" | | echo "Yes"
Yes

--> xiaoa= "ABC"; Xiaob= "W"; [["${xiaoa/${xiaob}/}" = = "$XiaoA"]] && echo "No" | | echo "Yes"
No