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The terminal

The following work under the standard bash shell. The most convenient way to open a terminal is through for example click on the icon representing the shell, but note that text mode terminals are usually available.

  • Ctrl + Alt + F1 to F7 - Text modes
  • Ctrl + Alt + F8 - Graphical mode

http://linux.org.mt/article/terminal

http://www.ee.surrey.ac.uk/Teaching/Unix/

The essentials

Command Effect
cd .. Change directory "up" on level
cd Change directory to home directory
cd - Change directory to previous directory
cd my/path/ Change directory to my/path/ residing in the current directory
cd /usr/bin/ Change directory to /usr/bin/ (the first / makes this an "absolute" address)
pwd Displays current directory
ls List files in current directory
command --help Short manual for a command
info command Verbose manual for a command
man command Show the full manual
./excutable Execute the file called executable, residing in the current directory
echo "test" Will print "test" to the screen
chmod +x file Make file exacutable (chmod changes access permissions)

Display text

cat

cat can be used to

  • Display text files on screen.
  • Copy text files.
  • Combine text files.
  • Create new text files.

Examples:

  • cat filename - Display text in terminal
  • cat file1 file2 > newcombinedfile - Combine file1 and file2 to newcombinded (> is a general symbol used to direct the output)

http://www.cyberciti.biz/faq/howto-use-cat-command-in-unix-linux-shell-script/

less

The less command enables you to scroll the content (press q to exit)

Redirecting output

The > operator can redirect output. It can be used to print the output to a file rather than to the screen. For example:

ls > myfile

will write the standard output ls to the file myfile.

  • >> - append to a file
  • command > file 2>&1 - The 2>&1 will redirect both the standard output and the error output

File commands

Command Effect
mkdir name Makes new directory
rmdir name Removes (empty directories)
mv name newname Renames/moves a file
mv name1 name2 dir Move files
file name Displays type of file
locate file Locates a folder (faster than find due to write to a database, but not standard)
rm -rf file -f removes forcefully, -r removes recursively
cp file1 file2 Copy file1 to file2
cp -r file1 file2 Copy file1 to file2 recursively (i.e. when copying directories)
scp file1 file2 Secure copy file1 to file2 (usually used when copying over networks, for example if file2 is user@server:/path/

One can compress (zip) a file with

tar -zcvf compressedName.tar.gz filesOrFolders

where

  • -z - Compress archive using gzip program
  • -c - Create archive
  • -v - Verbose i.e display progress while creating archive
  • -f - Archive File name
  • Use -x to extract

Environmental variables

Variables available in the terminal

Command Effect
export myVar=5 Assign 5 to the variable myVar
export myVar2=python Assign python to the variable myVar2
echo $myVar Echoes the variable myVar
$myVar2 Calls the command stored in myVar2
$HOME Variable which stores the users home directory
$SHELL Variable which stores the shell
$PATH Variable which stores where to search for commands (executables) like ls
$PS1 Tells what to display in prompt
set Views all current environment variables

NOTE: Aliasing can be used to redefine commands (this can be stored in ~/.bashrc so it doesn't need to be written every time. For example

alias ls="ls -a"

Sets ls -a to ls

Keyboard shortcuts

Stroke Effect
Ctrl+r text Reverse search. Press Ctrl+r repeatedly to search backwards
Ctrl+c Cancel
Ctrl+Shift+x Cut
Ctrl+Shift+c Copy
Ctrl+Shift+v Paste

Processes

Command Effect
top Monitoring processes by cpu usage, can also task manage from there
ps aux Watch all processes
kill <process id> Terminates process
time Gives how much time the program is using
nice -n 1 <operation> Setting the nice value. A high value means high priority. Example: nice -n 1 python myScript.py

http://www.cyberciti.biz/faq/show-all-running-processes-in-linux/

Shebang line

If #! is written in the first line of a script, this line is called the shebang line. This line tells the program loader which interpreter to use. For example

#!/usr/bin/env bash

Tells the program loader to use bash which is found in the current environment