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ADVENTURES

IN TEXT

ModifyingCommandBehaviour

The way thatcommandsbehave can be altered by using

flags,argumentsand operators.Flagscan be a singleletter

precededby a dash,or a text stringprecededby two dashes

(e.g.-a or --all).

As an example,ls lists the contentsof the current directory,

but it’s mademore usefulby usinga flag (e.g.ls -a will list all

files,evenhiddenones.In Linux,any file precededby a dot is

normallyhidden).Theseare usuallyconfigfiles or directories

containingprogramdata).ls -l will showfiles withmore

detailedinformationin a formattedlist.

Flagscan be combined.For example,ls -la will showa

formattedlist of all files,including‘hidden’ones.

Argumentsare not heateddiscussions,but data,suchas a

file name.Theycan be usedto definea file to be altered in

someway or containinformationthataltersthe outputof the

command(e.g.cd has the targetdirectoryas an argument,as

in cd /Pictures). By default,commandsoperateon files in your

current directory, but you can also use the completepathto

a file in anotherdirectory(e.g.ls /etc/networkwill list the

contentsof the /etc/networkdirectory).

Operatorsare usedto manipulatethe outputfrom a

command.Theseare specialcharacters,suchas & = + > < ; |

etc. Thesecan be veryuseful,as we shallsee laterin

the series.

Nearlyall commandshavesomesort of associatedhelpfile.

The simplestis accessedby typingthe commandfollowedby

--help,whichgivesa basicguideto the command’s syntax

(e.g.ls --helpwill list all the availablecommandoptions).

If you wantmore in depthinformationtypingmanfollowed

by the command(e.g.manls will displaya scrollablemanual).

Manycommandsalso havea Texinfofile, whichcan be

calledup usingthe info command.ls is partof the coreutils,

so typinginfo coreutilswill showyou the full documentation

for thatcompletepackage,whichcan be navigatedwiththe

cursorkeys.

Whenyou’vefinishedwiththe terminal,you can closeit

by typingexit.If you wantto closedownthe computer, the

commandis shutdown-h now. If you get permissiondenied,

sudoshutdown-h nowshouldwork.Typingshutdown-r now

will restartthe PC.

As yourknowledgegrows,you will startto gain

understandingof howyouroperatingsystemworksand more

confidencewhendealingwithit. If you makea mistake,often

all that’s neededis to retraceyourstepsand you’llrealise

where you’vegonewrong.

In the nextarticle,we’lllookfurtherinto the commandline

to examinemore commandsand theiruses.mm

Once connected to a

remote sshterminal, you’re

logged in as if youwere sitting

at theother computer’s

terminal screen

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iTheRaspberryPIis anidealdeviceforexploringtheLinuxshell

iTheVirtualboxinterfaceanda Xubuntuvirtualmachine