unix Getting Started with Unix Commands A non exhaustive list of Unix commands


$man <command>

Displays the on-line manual pages for the command


Clears the terminal screen


Returns the working directory name

$echo <string>

Writes the string to the standard output

$printf <string>

Format and print the string Example: print $PATH $printf “%s\n” $PATH


Show how long system has been running

$which <program>

Locate a program file in the user’s path

$whereis <program>

Checks the standard binary directories for the specified programs, printing out the


$cd [directory] 

Change directory Commonly used directory symbols:

  • . : Current directory
  • .. : Parent directory
  • ~ : Home directory
  • / : Root directory
  • $ls -a : Show hidden files

  • $ls -l : Show long list

  • $ls -1 : Show just the filename per line

  • $ls -h : Human readable format

    $file Determine file type (e.g. gzip)



Display content of a file one screen at a time
spacebar : Scroll to next screen; b=previous screen
enter : Scroll one line
h : Help for more
q : Quit help

$less <file>

Less is a program similar to more, but which allows backward movement in the file as well as forward movement

$cat <file>

Reads files sequentially, writing them to the standard output

$head [-number] <file>

Display first lines of a file

$tail [-number] <file>

Displays the contents of file or, by default, its standard input, to the standard output

  • $tail -f : View changes in file in real-time
$touch <file>

Sets the modification and access times of files. If any file does not exist, it is created with default permissions

$tee <file>

Copies standard input to standard output. Press ctrl-d to stop adding content

  • $tee -a : Append the output to the files rather than overwriting them
$mkdir <directory>

Create a directory


Display the number of lines, words, and bytes contained in each input file, or standard input

  • wc -l : Count lines
  • wc -w : Count words
  • wc -m : Count characters
$diff <file1> <file2>

Compare two files line by line. Will print only the different lines.

$locate <file>

Locate files on disk

  • $locate -q : suppress errors
$find <path> <expression> <action>

Search for files by name or content

  • $find -name : Find by filename
  • $find -size <+/-n> Example: Find files in current directory that are larger than 10k $find . -size +10
$rm <file or directory>

Delete <file or directory>

  • rm -f : Skip confirmation
  • rm -i : Approve each deletion
  • rm -r : Recursive

Example: Delete the and it’s content $rm -r

$mv <source_file> <target_file>

Renames a file

$mv <source_file> <target_directory>

Moves a file

  • $mv -i : Don’t override exiting files
  • $mv -r : Recursive

Example: move directory up in hierarchy $mv ..


Copy a file/directory within the same machine (Use scp command to copy to a remote machine)

  • $cp -i : Don’t override exiting files
  • $cp -r :recursive

Example: Copy and rename a file

$cp <file_name> <new_file_name>

Example: Copy to directory

$cp <file_name> <directory_name>

Example: Copy and rename a directory

$cp -R <directory> <new_directory>

Example: Copy all files of specific type to a directory

$cp *.txt <directory>

$ln -s <file> <link name>

Create an alias (link) to a file

  • $ln -s : Create a soft link (A link that functionas across machines)
$sort <file>

Sort the content of a file -r reverse sorts -n numeric sort

Example: sort the and write the result to sorted.txt $sort | uniq -u > sorted.txt

$uniq [-ucd] filename(s)

Looks for duplicate lines. Data must be sorted first

  • $uniq -d : show only one copy of the duplicate lines
  • $uniq -u : Show only lines that are not duplicate
  • $uniq -c : Output each line preceded by a count of occurrences Example: show users that are connected more than once $who | cut -d’ ‘ -f1 | sort | uniq -d
$grep <pattern> <file_name> 

Prints lines that contain a match for a pattern.

  • $grep -i : Perform case insensitive matching
  • $grep -v : Prints all lines that don’t contain the regex
  • $grep -r : Recursively search subdirectories listed and prints file names with occurrence of the pattern
  • $grep -I : Exclude binary files
$tr “string1” [“string 2”]

Search and replace tool. tr only accepts its input from pipes and redirections. it doesn’t accept files as input.

  • tr -d : Delete all occurrences of all CHARACTERS in string1

Example: Print a.txt to screen after deleting all occurences of “;” $cat a.txt | tr -d “;”

  • tr -s : Replace occurrences with a single character

Example: $echo “SSSS SS” | tr -s “S” “S”


Creates and manipulates streaming archive files. This implementation can extract from tar, pax, cpio, zip, jar, ar, and ISO images and can create tar, pax, cpio, ar, and shar archives.


$du [file or directory]

Display the file system block usage for each file or directory. If no file/directory is specified, the block usage of the current directory is displayed.

  • $du -a : Files & directories (default is directories only)
  • $du -h : Human readable format Example: Display disk usage, ordered, only MB files $du -h | grep -i “m\t” | sort -n Example: Find out top 10 largest file/directories $du -a /var | sort -n -r | head -n 10

Display free disk space

  • $df -h : Human readable format


> Redirect standard output. Dont overwrite file if it exists

>! Redirect standard output. Overwrite file if it exists

>& Redirect standard output and standard error

Example: Redirect command output into a file

$ls > result.txt

Use > /dev/null file to dispose of errors message

Example: Find a file named my_file_name and print the result to ~/find.txt; Hide errors (e.g. “permissions denied”)

$find / -name my_file_name.* > /dev/null > ~/find.txt

< Redirect standard input

>> Append standard output <command> >> : Append output to the end of an existing

<command> < : Redirect input to a command from a file

| Redirect standard output to another command (pipe)

Example: Show paginated details of running processes

$ps -ex | more

| : Pipe output of command1 to be the input of command2 (If an output file is desired in the middle of a pipe use the tee command)

Example: Count the number of connected users

$who | wc -l



Show active processes

  • $ps -e : Show information about the process
  • $ps -x : Show hidden processes

Example: Find processes by name $grep -l <process_name_regex>

$kill [-signal] pid

Kill a process.

Some of the more commonly used signals:

  • 3 : QUIT (quit)
  • 9 : KILL (non-catchable, non-ignorable kill)
  • 15 : TERM (software termination signal)

Display and update sorted information about processes See man pages for list of possible keys. common keys are: cpu, threads, ports

  • $top -o

Display and update sorted information about processes


$sudo <command>

Execute the command as a super user


(substitute user) opens a session as an admin


Exit root


Display effective user id


Print all connected user names


Change password

$chmod <who> <operation> <permissions> <file or directory name>

Change owner/group access to a file or directory

Who: u user; g group; o other; a all above

Operation: + add; - remove; = set (meaning reset to nothing and set only what was specified)

Permissions: r w x

Example: Adds read/execute permissions to group

$chmod g +rx <file>


$chmod 743 <file>

Note that to $cd into a directory you need the x permissions