COMP 206: BASH and UNIX

System

set of interconnected components (also called artifacts)

OS

software that lets you interact with computer, manages resources, and provides libraries

POSIX Standard

Portable Operating System Interface

• OS Application Programming Interface and System Interfaces

• Utilities

• Programming Libraries

• Command Interpreter

Unix OS Components

kernel, file system, shell, utilities

Kernel

RAM: Login, runs programs, basic common interface, memory management

File System

part RAM, part disk: Defines the way the disk drive is formatted, file allocation table, data structure that makes files real, reads and writes to disk, interacts with files based on user commands.

Shell

A user interface, global memory, commands to interact with OS

Utilities

Additional OS commands and programs, third party commands and programs

RAM contains (3)

Kernel, File System, Login

Disk contains (2)

shell, utilities

Login on Failure

Failed Login is recorded in utilities

Login on Success

Access the shell and replaces login with bash

Shell Functions

get user input, display OS info, store session information

Home Directory

Top folder in users directory tree (~)

Root Directory

Top folder in OS (/)

Current Directory

Directory currently within (.)

Parent Directory

Directory above the current directory (..)

Absolute Path

String begins at root

Relative Path

String begins at current location

Command Format

<Program> <switches> <arguments>

echo

prints message to terminal and can be quoted

directory listing

(ls) lists items in dierctory

long form listing

(ls -l) <permissions> <links> <owner> <group> <size> <modification date>

ls -a

display all files including hidden files

ls -l <file list>

see particular long format file

pwd

displays current directory path

cd <directory name>

change directory, must be accessible from current directory (or have right path)

mkdir [switches] <directory name>

makes a new directory

rmdir [options] directory

removes a directory

touch [options] file

creates a new empty file

cp [options] file1 file2

copies file 1 (file or file path) to file 2 (path, file or filepath) (creates or overwrites file 2)

mv [options] file1 file2

move file 1 into file 2

rm [options] file

removes a file or directory (need switches for directory)

cp/mv/rm -i

interactive: prompts for confirmation before proceeding

cp/rm -r/R

recursively visits directory, first visitiing files and subdirectories beneath it

mv/rm -f

Force: don’t prompt for confirmation

cat [options] files

file concatenate and display result

less [options] file

page through a text file

[command] > path

redirects the output of command to file at path (overwritten)

[command] » path

redirect output of command, appending to file at path

command1 | command2

redirects output of command1 to input of command2

logout

closes shell and logs you out

exit

closes shell and sends you to shell used to start exited one

ctrl+C

Terminates Programs

ctrl+D

Stop waiting for input

*

replaces any pattern

?

Replaces single character

square brackets []

any character within the brackets

[x-y]

character range

[!x]

matches any single character except x

globbing

passing input to program and expands wildcard matching patterns within segments BEFORE calling the command (shell does the work)

result when globbing fails

literal wildcards sent to program

grep [option] <string> <file list>

searches for occurrences of the string (surround with single quotes to avoid expanding wildcard or variables)

sed [options] <file list>

stream editor for editing files

awk [options] <file list>

scans for patterns in a file and processes the results

grep -i

ignore case

grep -c

returns count of number of lines containing matches

grep -v

inverts the search (displays only ones that do not match)

grep -n

displays line number along with lines with matches

grep -l

lists filenames but not lines

grep -E

pattern uses extended syntax

grep -e

followed by pattern

grep ^

anchor: matches beginning of string/line

grep $

matches end of string/line

(?#…)

comment “…” is ignored

(?:…)

Matches but doesn’t return “…”

(?=…)

matches if expressions would match “…” next

(?!…)

Matches if expression wouldn’t match “…” next

?

match 0 or one occurrences of previous item (use backslash)

+

match one or more occurrences of previous item (use backlash)

*

match zero or more occurrences of the previous item (use backslash)

.

any character except newline

STDIN

Standard In: keys typed by user are gathered

STDOUT

Standard Out: normal application output

STDERR

Standard Error: error output

<

Content of file sent as input to program

2>

Redirects standard error

Nested Execution

$(…)

tee

redirects to 2 places: <command> | tee <destination1> | <destination2>

File

single document in disk storage

TAR

(.tar) Collection of files stored within a single document

ZIP

(.zip) Single compressed document in disk storage

Archive

(.gz) collection of zip files in a single file

tar tool

combines several files into single file

gzip tool

compress a single file

.tar

tar archive file

.tgz

compressed tar archive file

tar -c <archivename> <filename>

creates a new tar archive

tar -r <archivename> <filename>

updates tar archive

tar -x <archivename> <path>

extracts from tar archive

tar -f <archivename> <path>

specifies archive file name

tar -v

activates verbose mode

tar -z

allows you to compress the archive

diff [options] file1 file2

compares two files

ln <filepath> link_name

creates hard link to file/folder (like giving file another name- points to the same same in disk) (can only delete once all hard links are gone)

ln -s <filepath> link_name

creates symbolic link, new file that automatically redirects to target file (deletion does not affect target file)

sort [options] file

sorts the lines of the file

wc [options] [file(s)]

displays a word/character/line count

File Owner

each file is owned by a use and a group

File Permission Groups

user, group and other