Shell Script--Grammar Chapter

Condition test

1. Test condition tests or [] (test conditions are true false)

Example: string comparison #!/bin/bash Read data Test "$data" = = "Hello" //note there are spaces on either side of the equal sign or [$data = = "Hello"] echo $? //Run result of previous command, success is 0, failure is 1 650) this.width=650; "title=" QQ picture 20160810202257.png "Src=" http://s4.51cto.com/wyfs02/M00/85/A7/ Wkiol1erhr-x9mkjaaarfnpmpza433.png "alt=" Wkiol1erhr-x9mkjaaarfnpmpza433.png "/> Example: two number comparison size #!/bin/bash data=200 [$data-eq 100] echo $? [$data-LT 100] echo $? [$data-le 100] echo $? [$data-GT 100] echo $? [$data-ge 100] echo $? 650) this.width=650; "title=" QQ picture 20160810204114.png "Src=" http://s4.51cto.com/wyfs02/M02/85/A7/ Wkiol1eriodxbmfqaaaizovh3ks109.png "alt=" Wkiol1eriodxbmfqaaaizovh3ks109.png "/> 650) this.width=650; "width=" 384 "height=" "title=" QQ picture 20160810205512.png "style=" width:351px;height:220px; "src= "Http://s5.51cto.com/wyfs02/M02/85/A7/wKioL1erI5LBwmBYAADtOBsIJ0w427.png" alt= " Wkiol1eri5lbwmbyaadtobsij0w427.png "/> 650) this.width=650; "Width=" 609 "height=" 146 "title=" QQ picture 20160810205711.png "style=" WIDTH:530PX;HEIGHT:147PX; "src= "Http://s2.51cto.com/wyfs02/M02/85/A8/wKiom1erJHrg86p2AADIymt-B98039.png" alt= " Wkiom1erjhrg86p2aadiymt-b98039.png "/> For example: Test and, non-logical operations 650) this.width=650; "Width=" 522 "height=" "title=" QQ picture 20160810211610.png "style=" width:518px;height:330px; "src= "Http://s3.51cto.com/wyfs02/M00/85/A8/wKiom1erKMzTXNOMAADCx0Y4Cxc703.png" alt= " Wkiom1erkmztxnomaadcx0y4cxc703.png "/>

2, If/then/elif/else/fi

#!/bin/bash Read data If ["$data"-eq];then echo "100" elif ["$data"-eq];then echo "200" Else : //: Empty command, the command does nothing Fi 650) this.width=650; "title=" QQ picture 20160810213411.png "style=" Float:none; "src=" http://s2.51cto.com/wyfs02/M02/85/A7 /wkiol1erllgjd0fmaaauk_mqqu8914.png "alt=" Wkiol1erllgjd0fmaaauk_mqqu8914.png "/> #!/bin/bash Read data ["$data"-eq] && { //Set execution curly braces inside, otherwise execute brackets outside echo "Yes" Exit 0 } echo "No" 650) this.width=650; "title=" QQ picture 20160810214023.png "style=" Float:none; "src=" http://s2.51cto.com/wyfs02/M00/85/A8 /wkiom1erllgxqgylaaaouuykt9u657.png "alt=" Wkiom1erllgxqgylaaaouuykt9u657.png "/> #!/bin/bash Read data ["$data"-eq 100] | | { //Do not set execution curly braces inside, otherwise execute brackets outside echo "Yes" Exit 0 } echo "No" 650) this.width=650; "title=" QQ picture 20160810214551.png "Src=" http://s2.51cto.com/wyfs02/M01/85/A8/ Wkiom1erl3oiqm-saaapefc0lzc179.png "alt=" Wkiom1erl3oiqm-saaapefc0lzc179.png "/>

3, Case/esac

#!/bin/bash Read Val Case ' $val ' in Start | -S | -start | -start) echo "Start" ;; ' Stop ') echo "Stop" ;; ‘*‘ ) echo "*" ;; Esac 650) this.width=650; "title=" QQ picture 20160810220302.png "Src=" http://s5.51cto.com/wyfs02/M00/85/A7/ Wkiol1erm7piv8gjaaapzhkpyko362.png "alt=" Wkiol1erm7piv8gjaaapzhkpyko362.png "/>

Looping statements

1, For/do/done

Writing one: #!/bin/bash For i in {1..100} For I in {A.. Z Do echo "$i" Done Run Result: print a...z letters Two: #!/bin/bash For ((i=0;i<=100;i++)) Do echo "$i" Done Run Result: Print 1 ... 100 of the numbers

2, While/do/done && Until/do/done

650) this.width=650; "Width=" 614 "height=" "title=" QQ picture 20160810233640.png "Style=" width:610px;height:181px;float : none; "src=" Http://s2.51cto.com/wyfs02/M02/85/A9/wKiom1erSk2Bzg77AAATie7TUzw879.png "alt=" Wkiom1ersk2bzg77aaatie7tuzw879.png "/> 650) this.width=650; "Width=" 503 "height=" 164 "title=" QQ picture 20160810233955.png "Style=" width:611px;height:192px;float : none; "src=" Http://s4.51cto.com/wyfs02/M02/85/A9/wKiom1erSk2Aip4aAAASBYk-sWU286.png "alt=" Wkiom1ersk2aip4aaaasbyk-swu286.png "/> To find the even and the 1~100 between #!/bin/bash Sum=0 Ret=0 For i in {1..100} Do Let ret=i%2 If [$ret-eq 0];then Let Sum+=i Fi Done Echo $sum Run Result: 2550

3. How to debug shell scripts

Shell Script--Grammar Chapter