Linux Command Line Introduction for total beginners, Part 2

The$Linux$Command$Line$Interface(Bash&Shell)

Part%2Part%1%is%available%as%a%pdf%file%at%h2p://www.slideshare.net/corriewa29/linux=cli=1

Prepared'for'the'Nova'Sco0a'Linux'Users'Group'by'Corrie'Wa=,'Fall'2014

h"p://www.corriewa".com/

Iden%fying*Your*Directories

$ echo $HOME!....Tells&you&the&contents&of&shell&'environment&variable'&that&stores&your&home&directory&name;&get&to&it&by&$ cd ~$ cp books/afile.txt .!(a&single&dot)&....Copy&afile.txt&from&directory&books&to&the&current&directory$ cp books/afile.txt ..!(two&dots)&....Copy&this&file&to&the&parent&directory&of&the&current&directory&(the&level&above&the&current&dir)$ echo $PWD!....This&environment&variable&refers&to&the&current&working&directory;&the&directory&printed&out&if&you&type&$ pwd$ echo $OLDPWD!....Your&previous&working&directory;&get&to&it&with$ cd -

Doing&More&Things&with&Files

myputer:~ ccw$$ ls!....List&all&the&files&(including&directories)&in&my&home&directoryDesktopDownloadsemails_officeLNDpdfsLinuxBookspresentation1!....and&on...and&on...and&on...myputer:~ ccw$!....When&done&lis8ng,&the&command&prompt&is&returned,&ready&for&your&next&instruc8on&to&the&shell.

Command'Op*ons

Any$command$can$be$run$by$typing$the$command$name$and,$if$needed,$'arguments'++$(e.g.$filename).$The$command$will$run$with$all$op<ons$set$to$default$values.$Each$command$comes$with$op<ons$that$you$can$specify$a$value$for$(to$tailor$the$output$to$your$needs).$Type$in$'thecommand --help'$(two$dashes$in$front)$to$see$the$op<ons$available$for$any$shell$buil<n$command.

Op#ons'can'be'listed'individually'or'as'a'group,'always'preceded'by'a'dash:$ ls -l -a -t$ ls -lat!....Both&of&these&commands&do&the&same&thing.

Command'Op*ons,'using'ls'as'an'example

ls!....Lists&all&files&in&the&working&directory&except&special&hidden&files,&whose&names&begin&with&a&dot&(.)ls -l!....The&'-l'&(long)&op>on&tells&'ls'&to&give&more&details&about&files$ ls -l logo1.png-rw-r--r-- 1 ccw staff 3475 15 Mar 18:14 logo1.png!......The&'-'&indicates&a&file;&'-rw-r--r--'&consists&of&3&groups&of&permissions:&1)&Read&+&Write&for&owner&(ccw)&'rw-';&2)&Read&Only&for&group&(staff)&'-r-';&3)&Read&Only&for&the&world&'-r-';&the&'3475'&is&file&size&(in&bytes);&'15'&is&the&number&of&disc&blocks&it&occupies;&'Mar 18:14'&is&last&modifica>on&date.

More%'ls -l'%....$ ls -l C_pra!<tab>!....Remember'to'use'the'<TAB>'key'for'auto6comple:on'of'your'filename!$ ls -l C_practice-rw-r--r-- 1 ccw staff 221 1 Sep 19:33 ex1.c-rwxr-xr-x 1 ccw staff 8496 1 Sep 13:23 ex3.1-rwxr-xr-x 1 ccw staff 8496 30 Aug 18:41 hi-rw-r--r-- 1 ccw staff 76 30 Aug 18:41 hi.cdrwxr-xr-x 2 ccw staff 68 10 Sep 11:38 tests....The''d''indicates'that'this'file'is'a'Directory;'The''x''is'execute'permission'(permission'to'enter'and'access'files'in'this'directory)

Some%more%'ls'%op)ons...

$ ls -Fex1.c ex3.1* hi* hi.c tests/The$op'on$'-F'$shows$directories$with$a$trailing$'/'$and$executable$files$with$a$trailing$'*'

$ ls -R!....List&all&subdirectories&encountered:&this&would&list&all&files/directories&in&'tests/',&and&all/any&files&in&its&subdirectories.

ls -lRa!....Op$ons(used(as(a(group(preceded(by(a(dash

For$more$op(ons$to$use$with$'ls',$see$h2p://ss64.com/bash/ls.html.

Help!&...&It&won't&let&me&run/modify&my&own&file!

This%is%usually%due%to%a%lack%of%proper%file%permissions.Check&your&permissions:$ ls -l ex3tester.1-rw-r--r-- 1 ccw staff 8496 1 Sep 13:23 ex3test%....You$have$Read$+$Write$permission$only$($rw8$).Edit&them&with&the&'chmod'&(Change&Mode)&command:chmod u+x ex3test%....Add$execute$permission('x')$to$user$('u')$ ls -l ex3test%....Check$the$new$permissions-rwxr--r-- 1 ccw staff 8496 1 Sep 13:23 ex3test%....Now$you$have$execute$permission!$($rwx$)

The$'chmod'$command$has$several$op0ons,$of$course.A$very$useful$one$is$'-R'$(Recursive),$which$lets$you$modify$the$permissions$for$an$en0re$directory$(it$makes$the$requested$permission$changes$in$all$subdirectories$and$files$of$the$directory),$i.e.$'change$mode$on$files$and$directories$recursively'.

For$a$good$introduc-on$to$'chmod',$see:h"p://catcode.com/teachmod/chmod_1.html1(Tutorial)h"p://ss64.com/bash/chmod.html

“It's&easier&to&ask&forgiveness&than&it&is&to&get&permission”~"Rear%Admiral%Grace%Hopper"(A%pioneering%20th%century%computer%geek;%check%her%out%on%YouTube!)

Wildcards)(file-matching)with)metacharacters)

Wildcard(characters(used(with(shell(commands(can(save(you(major(typing/searching(8me(by(le:ng(you(specify(in(one(short(character(sequence(that('This&is&the&sort&of&thing&I&am&looking&for'.

The$shell$will$'expand'$your$wildcard$characters,$then$find$everything$that$matches$your$request.$Your$command$(such$as$'mv',$'cp',$'rm'$and$many$others)$can$use$wildcards$to$perform$ac@ons$on$more$than$one$file$at$a$@me,$to$find$all$files$with$certain$characteris@cs,$and$more.$Useful$stuff!

Wildcards:*the*ques0on*mark

• ?"(ques(on"mark)"....represents(any(single(character.Ex.$1:"$ rm hd??"....would(do(a(search(for(all(four3character(filenames(star6ng(with('hd'.It(would(find"hda1,"hdbd,"hdct"and(every(other(le<er/number(between(a3z,(039,(then(remove((delete)(them.

Wildcards:*the*asterisk

• *"(asterisk)"....for%any%number%of%characters%(zero%or%more%characters).

Ex.$1:!$ rm cf*!....would'delete!'cfa.txt',!'cfprom.jpg',!'cfcollection.odt'!....(whatever'starts'with''cf','including''cf''itself).

Ex.$2:!$ rm m*l!....would'delete!'ml',!'mill',!'mysqltool',...!(whatever'starts'with'an'm'and'ends'with'an'l)

A"good"beginner's"reference"with"examples:h"p://mylinuxbook.com/83examples3of3wildcards3in3bash/

Wildcards:*square*brackets

• [ ]"(square"brackets)"....specifies(one(of(this(range(of(values.Ex#1:"Ask(for"m[aou]m"....you(could(get:(mam,(mum,(momEx#2:"Ask(for"m+([a/d])m"....(it(can(become(anything(that(starts(and(ends(with(m(and(has(any(character((+(means('one(or(more(of')(a(to(d(inbetween,(such(as(madam,(madm,(mdm,(mbabcm.

In#other#words:!....Find&me&anything&that&(in&Ex&1):contains&an&**a**&or&**o**&or&**u**,&or&(in&Ex&2):&starts&with&m&and&then&contains&any&of&the&characters&from&a#to#d&(one&or&more&occurrence&of&them),&and&ends&with&m.

Wildcards:*curly*brackets

• { }"(curly"brackets)"....The%terms%are%separated%by%commas%and%each%term%must%be%'the%name%of%something'%or%a%wildcard.$ cp { } ~%_....%will%copy%anything%that%matches%either%wildcard(s),%or%exact%name(s)%to%this%user's%home%directory.

This%would%be%valid:Example:%$ cp {*.doc,*.pdf,admin.php} ~%....This&will&copy&anything&ending&with&'.doc'&or&'.pdf'&and&the&file&named%admin.php%to&the&user's&home&directory.&Note&that&inside&{&},&spaces&are&not&allowed&a<er&the&commas&(or&anywhere&else).

Wildcards:*'{ }'*con.nued,*and*'[! ]'

$ touch course{1,2,3,4,5}!....create'mul+ple'new'files$ lscourse1 course2 course3 course4 course5

[! ]!(square'brackets'containing'exclama3on'mark)!....specifies(a(range(of(values(to(EXCLUDE.!....Similar(to(the([(],(but(it(says("Accept(as(a(match(anything(that(does)not)contain(the(characters/range(listed(between(the('['(and(']'.Ex.'1:!'$ ls course[!4]'!....will(list(all(course?((ie.(course1,(course2,(course3,(etc),(EXCEPT(for(a(file(with(the(number(4(terminaOng(its(name.

Command'Line'History'00'use'it'to'work'faster

The$Bash$history$func,on$runs$behind$the$scenes,$adding$each$command$you$run$into$the$equivalent$of$a$linear$database.

You$can$then$scroll$through$it$using$the$up$and$down$arrow$keys$or$display$in$its$en5rety$by$typing$in$history$at$the$command$prompt.

By#default#it#saves#your#last#500#commands.

Searching*for*Files*using*'find'

To#find#files#by#name,#you#can#use#the#'-name'#op5on.#The#search#is#done#by#the#file's#basename#(the#file's#name#without#the#directories#that#are#part#of#its#path);#the#directory#names#are#not#searched#by#default.

Syntax:!$ find /path/to/dir -name "filename"Ex.*1:!$ find /etc -name "httpd.conf"Ex.*2:!$ find /projects -name "*.html"As!seen!in!Ex.!2,!you!can!use!file3matching!characters,!such!as!asterisks!(*)!and!ques?on!marks!(?)!when!all!members!of!a!par?cular!group!of!files!are!wanted.

Searching*in*Files

For$searching$in$files$for$a$search$phrase$or$term,$you$can$use$the$grep$command.$With$grep,$it$is$easy$to$search$a$single$file$or$to$search$a$whole$directory$structure$of$files$(a$recursive$search).

$ grep "thisword" /Documents/CS-Books$ grep -i "thisword" /Documents/CS-Books!....The!'-i'!makes)the)search)case-insensi0ve.

There%is%a%LOT%more%to%'grep'%than%this,%enough%for%another%presenta5on!

Tips

• Un$l&you&know&how&to&deal&with&them,&do&not&use&Bash&'special&characters'&or&blank&spaces&in&filenames.

• Use&the&TAB&key&for&filename'auto+comple.on&(prevents&filename&errors,&speeds&things&up).&If&you&hear&a&beep,&press&TAB&again:&a&list&of&possible&comple$ons&is&returned.&Type&in&more&characters&of&your&filename&$ll&it&becomes&'the&only&choice'&leF.&Press&TAB&again.

• Use&wildcard&characters&(with&care,&if&using&rm!!!)&to&speed&up&your&work.

Tips,&con*nued

• Use%the%up%and%down%arrow%keys%to%scroll%through%previous%commands,%stop%on%the%command%you%want%(edit%it%if%you%like),%press%ENTER%to%run%it.

• If%a%command%is%returning%a%tooBlong%list%of%results,%use%ControlBC%to%stop%the%command%from%conDnuing%to%spew%forth.%Your%command%prompt%will%reappear.

• If%you%type%a%command,%hit%Enter,%and%get%the%shell%prompt%back%without'anything'appearing'to'happen,%it%means%your%command%executed%successfully.%If%there%was%a%problem,%you%will%get%an%

So#what#is#the#command#line#really#good#for?

How$about$doing$arithme1c?

$ echo $((31+11))42!....The%Answer%to%Life,%the%Universe%and%Everything

Next%Up%(possibly):%Create%your%own%commands%using!'alias',%as%well%as%the%coolest%CLI%feature%ever:%I/O%RedirecDon