unix command line

Mastering the UNIX Command LineHoward Mao March 28, 2013... More About PermissionsI Three types of permissions: read r, write w, execute x I Three categories: user u, group g, other o I

Mastering the UNIX Command Line

Howard Mao

March 28, 2013

I Created by Ken Thompson and Dennis Ritchie in 1970

I Modern descendants include Linux, OSX, and BSD

Looking up Information

I Man Pages: man <command>

I Google is your friend

I Stackexchange Sites

I stackoverflow.com

I serverfault.com

I superuser.com

I unix.stackexchange.com

Basic Filesystem Navigation

I look around - ls

I move about - cd, pushd, popd

I move, copy, delete - mv, cp, rm

I file info - stat, du, file

I changing permissions - chmod, chown

More About Permissions

I Three types of permissions: read (r), write (w), execute (x)

I Three categories: user (u), group (g), other (o)

I Also represented by an octal number: read (4), write (2), execute (1)

I Add them together to get number One octal digit for each category

I Ex 644 means read + write for user, read only for group and other, execute for nobody

I Execute permission for directory means you can list files in directory

I Match everything *

I Choices {foo,bar,baz}

I Characters [abc]

I Numbers {0 5}

The Almighty Find

Find allows you to search for files

I By Name: find -name \*.txt

I By Type: find -type d

I By Timestamp: find -mtime 1

I And many many more

Can also run commands on files find -name txt -exec rm {} \;

I/O Redirection

I I/O Commands: echo, cat, less

I Input from File: command < input.txt

I Output to File: command > output.txt

I Pipes : command1 | command2

I Search lines with grep

I Find and Replace with sed

I Select columns with cut and awk

Manipulating Processes

I Start in background: command &

I One after another: command1; command2

I If successful, then: command1 && command2

I If unsuccessful, then: command1 || command2

I Suspend and resume: command <Ctrl>+Z; [bg|fg]

I See running procs: ps, ps -au $USER, ps aux

I Server info - ping, traceroute, host, whois

I Sending raw traffic - nc, telnet

I The World Wide Web - wget, curl

I What’s my address? - ip addr, ip link

I What ports are open - ss, nmap

I Who’s on the port - lsof

I Believe it or not, the shell is turing complete

I Variables : VAR=abc

I If statements : if [ "$VAR" ]; then echo $VAR; fi

I For loops : for i in {1 5}; do echo $i; done

I While loops : while true; do echo "forever"; done

I User input : read var; echo $var

I Functions : function func () { do something }