A summary of several cold knowledge of the shell (IFS, arrays, substitutions, splits, lookups)

Ifs:

A direct description of the usefulness of IFS, details of what ifs is doing ... Self Google

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

Then we look at LS:

--LSA  a A

Is this.

Then if we need to write a script to manipulate each file:

--For I in $ (LS); Do echo "$i";d oneaaa

But the result is, obviously, inconsistent with our demands.

Because the value of IFS is a space, a tab. Enter. So here we turn a A into 2 a.

But we changed the IFS after the following example:

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

Well, that's what we're going to do, this time with ' \ n ' for the cut.

Array:

A script to illustrate:

#!/bin/bash# *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*# > author:xiaojunyu/lunaw# > Mail: [email&n Bsp;protected] # > Gmail: [email protected] # > blog:http://blog.csdn.net/lunaw# > Web:http://lun aw.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 ") # 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 the Name in ' seq 1 ${#SelectPackages [*]} ' do packagename= ' config_package_${selectpackages[$ (expr $Name- 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/# ${packagename} was not set/${packagename}=y/g ". C            Onfig echo-e "\e[01;36mreplace (${packagename}=y) done!" else Echo-e "\e[01;31mnot Found (# ${packagename} is not set)" echo "${packagename}=y"            ;>. 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 ${#UnSelectPackages [*]} ' do packagename=" config_package_${unselectpackages        [$ (Expr $Name-1)]} " if [[' Cat. config| grep ' # ${packagename} is not set ' | wc-l ' = = 0]]; Then Echo-e "\e[01;31mnot Found (# ${packagename} are not set)" If [[' Cat. config| grep "${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 (# ${packagename} is not s            ET) done! " else Echo-e "\e[01;31mnot Found (${packagename}=y)" echo "# ${packagename} is not set"            ;>. config echo-e "\e[01;36madd (# ${packagename} is not set) done!" Fi else Echo-e "\e[01;33mfound (# ${packagename} is not set)" Fi doneelse echo-e "\E[01;  31mNot Found. config "fiecho-e" \e[01;00m+---------------------------------+ "ECHO-E" \e[01;00m|  Don't worry about it, it's just a few packages to choose from! |" Echo-e "\e[01;00m+---------------------------------+" Sleep 1

Replace:

Single replacement

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

All replacements

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

Delete

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

Split:

There are several ways. The first type:

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

Output:

Xiaojunyu

But if that is the case:

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

Output:

Xiaojunyu

Not the way we expected. Then another kind of cutting method

Ifs method:

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

Output:

Xiaoj Unyu

Find:

Find if a string includes a 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

A summary of several cold knowledge of the shell (IFS, arrays, substitutions, splits, lookups)