Unix Notebook

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Introduction

1. Types of Unix

• Sun Solaris
• GUN/Linux
• MacOS X

2. Three parts of Unix operating system

• Kernel - allocates time and memory to programs and handles the folestores and communications in response to system calls
• Shell - an interface between user and the kernel, a command line interpreter (CLI)
• Programs

Everything in UNIX is either a file or a process

• A process is an executing program identified by a unique PID (process identifier).
• A file is a collection of data. All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root (written as a slash / )

Listing files and directories

• ls —list files and directories
• ls -a —list all files and directories including hidden files beginning with a dot
• mkdir —make a directory
• cd . —stay current directory
• cd .. —change to parent directory
  
• cd —change to home directory
• cd ~ —change to home directory
• pwd —show the working directory

Handling files

• copy file: cp originallfile destinationfile
• move file: mv originallfile destinationfile
• remove file: rm filename
• remove an empty directory: rmdir directory
• clear screen: clear
• display content of a file: cat filename
• display content of a file a page at a time: less filename. Press the [space-bar] if you want to see another page, and type [q] if you want to quit reading
• show the first ten lines of a file: head filename
• show the last ten lines of a file: tail filename
• search file:
  • search keyword: grep keyword filename
  • search a phrase or pattern: grep ‘phrase’ filename
  • serach keyword ignore case distinction: grep -i keyword filename
  • display lines do NOT match: grep -v keyword filename
  • precede each matching line with the line number: grep -n keyword filename
  • print only the total count of matched lines: grep -c keyword filename
  • use more than one option: grep -ivc keyword filename
• word count:
  • count numbers of words: wc -w filename
  • count numbers of lines: wc -l filename
• compress file: gzip filename (will create a file names filename.gz)
• unzip a file: gunzip filename
• read gzipped files:
  • for small file: zcat filename.gz
  • for large file: zcat filename.gz | less
• compare files: diff file1 file2
• find file:
  • by name: find . -name “*.txt" -print (search all files with extention .txt in the current directory)
  • by size: find . -size +1M -ls (find files over 1Mb in size, and display the result as a long listing)

Redirecting

• outputof a command: cat > filename
• append to a file: cat >> filename
• cconcatenate two files to a new file: cat file1 file2 > newfile
• input a file and sort then output as another file: sort < inputfile > outputfile
• check the current login user: who
• pipe the output of command1 to the input of command2: command1 | command2

example: Using pipes, display all lines of list1 and list2 containing the letter ‘p’, and sort the result.

cat list1 list2 | grep p | sort

Wildcard

• match any number of characters: *
• match one character: ?

Getting help

• read the manual page: man commandName
• one-line discription: whatis commandName
• match commands with keyword in their man pages: apropos keyword

Access rights

• check access right: ls -l

example: -rwxrw-r– 1 ee51ab beng95 2450 Sept29 11:52 file1

• If d is present, it will be at the left hand end of the string, and indicates a directory: otherwise - will be the starting symbol of the string.
• The 9 remaining symbols indicate the permissions, or access rights, and are taken as three groups of 3.
  • The left group of 3 gives the file permissions for the user that owns the file (or directory)
    
  • The middle group gives the permissions for the group
  • The rightmost group gives the permissions for all others.
• Owner of the file/directorry: ee51ab
• Group of the file/directory: eebeng95
• file size: 2450
• created time: Sept29 11:52
• file name: file1

Changing access right

• only the owner can use chmod to change the permission
• symbol:
  • user: u
  • group: g
  • other: o
  • all: a
  • read: r
  • write and delete: w
  • execute and access directory: x
  • add permission: +
  • take away permission: - examples:
• remove read write and execute permissions on the file biglist for the group and others: chmod go-rwx biglist
• give read and write permissions on the file biglist to all: chmod a+rw biglist

Jobs

• show a job list: jobs
• restart a suspended job: fg %jobnumber (fg restart the last suspended job)
• show process numbers: ps
• kill a job running in the forground: ^C (control c)
• suspend the job running in the foreground: ^z (control z)
• kill a suspenbded job with job number: kill %jobnumber
• kill a suspenbded job with job number: kill PID_number

NOTE: It is no possible to kill off other users’ processes/jobs!!