Definition

Unix

is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

Dennis Ritchie

Dennis MacAlistair Ritchie (September 9, 1941 – c. October 12, 2011)

unix

https://youtu.be/XvDZLjaCJuw

grep

https://youtu.be/NTfOnGZUZDk

Unix Commands

Listing files

• ls list files in current directory
• ls -l list files in a long format
• ls -a list all files (including hidden files) in current directory
• ls -F adds indicators to the list output to identify directories and different types of files.

For example ls -al would list all files in the current directory, including hidden files, in a long format.

Special characters

• . the current working directory
• .. the parent directory to working directory
• ~ your home directory
• / the root (top-level) directory. This is also the separator for directories
• * a wildcard meaning any string of characters
• ? a wildcard meaning any single character

Files

• cp file1 file2 makes a copy of file1 and calls it file2
• mv file1 file2 moves (renames) file1 to file2
• rm file1 removes (deletes) file1
• rm -i file1 asks for confirmation that you want to delete file1

there are the r and f arguments where r is for recursive and f if for force

Directories

• pwd print the working directory
• cd dirname change directory to dirname
• cd .. change to the parent directory of the current
• cd ~ change to your home directory
• mkdir dirname makes a new directory with name “dirname”
• rmdir dirname removes the directory with name “dirname”.
• rmdir -r dirname recursively removes directories and subdirectories

Text files

• cat file1 writes the whole of file “file1” to the terminal, also useful for concatenating files
• more file1 displays the file “file1” a page at a time
• less file1 a more versatile version of “more”
• head -30 file1 show the first 30 lines
• tail -25 file1 show the last 25 lines
• tail -f file1 show the last few lines and keep updating as the file grows
• wc file1 counts lines, words and characters in a file

control keys

• ctrl C interrupts whatever is currently running. (It can get you out of trouble at embarrassing moments)
• ctrl Z puts a foreground process into the background.
• ctrl S suspends current terminal
• ctrl Q resumes current terminal

Permissions

Unix allow to set ACL (access control list) to files. User ROOT (Super User) can do anything so can assign permissions. There are three sets:

• first byte of the set will give access to the OWNER of the file
• Second byte will give access to the GROUP beloging the file
• Third byte will give access privilege to anyone.

Permission bytes

List files

bash-3.2$ ls -la
total 72
drwxr-xr-x   7 sdipietr  staff    224 Mar 22 08:46 .
drwxr-xr-x  14 sdipietr  staff    448 Mar 21 14:38 ..
-rw-r--r--   1 sdipietr  staff   8196 Mar 21 14:42 .DS_Store
-rw-r--r--   1 sdipietr  staff  12387 Mar 21 16:50 05-Unix.html
-rw-r--r--   1 sdipietr  staff   3204 Mar 22 08:46 05-Unix.md
drwxr-xr-x   7 sdipietr  staff    224 Mar 21 14:53 images
-rw-r--r--   1 sdipietr  staff   1110 Mar 21 14:44 instituteStyle.html

Permission alias

• u user
• g group
• o others
• a all (equivalent to ugo)
• + gain
• - lose
• r read permission
• w write permission
• x execute permission

chmod chown

chmod changes file and directory permissions

• chmod u+r file1 change permissions of “file1” so user (“u”) gains (“+”) read permission (“r”).
• chmod -R 754 directory

chgrg change group ownership

• chgrp group1 file1 change “file1” to belong to group “group1”

chown change ownership

• chown -R root:user directory

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