$ date => Sun 9 Aug 2015 13:53:19 BST
$ ls
Applications Documents Library Music Public
Desktop Downloads Movies Pictures myFile
$ ls -A will list everything including invisible files
$ ls -lA will list everything including invisible files in long format (displays user permissions); shorthand for $ ls -l -A, combining multiple switches (or parameters) in one command (-l = long format; -A = all files)
$ pwd => /Users/andygout/desktop
$ cd .. => change to parents directory
$ cd . => change to current directory (i.e. do no change position)
$ cd documents/projects/command-line => change to most inner directory given by path
$ cd ~ => change to home directory
$ touch newfile.rb => creates this file in current directory
$ rm newfile.rb => removes this file (N.B. difficult to recover)
$ mkdir newdirectory => creates this directory in current directory
$ rmdir newdirectory => removes this directory (providing empty)
$ rmdir -r newdirectory => removes this directory and all files within it (-r switch = tells remove command to recursively remove all files within the directory as well as the directory itself)
$ rm -i => -i switch = interactive; will prompt you to confirm that you want to delete each file (useful for when you have lot of files but only want to delete a few)
$ rm -f => -f switch = force; will remove any file even if 'write protected'
$ cp newfile filecopy => two parameters required: file to be copied and name of the resultant duplicate
$ mv newfile ../newfile => two parameters: file to be moved (and its location) and location to where file will be moved (in this case the parent directory); if second parameter has different name then file will be renamed:
$ mv newfile filecopy => will essentially rename the file
$ cat file1 => will display file's text; cat = concatenate
$ cat > file1 => allows you to type text into a file but will delete all pre-existing text; end by hitting return then Ctrl-C
$ cat file1 file2 > combined => combines text of two files into new third file
$ less longtext.txt => displays a file with lots of text, allowing you to scroll up and down with keyboard to view entire document; quit by typing q
$ head -3 longtext.txt => displays first three lines only (with no parameter it will default to first ten lines, i.e. head longtext.txt)
$ tail -3 longtext.text => displays last three lines only
$ tail -f log.text => switch that allows you to watch last 10 messags of log (i.e. tail -f /private/var/log/system.log); Ctrl-C to stop tailing
$ man ls => provides manual for list function
KEYBOARD -> 1.stdin -> PROGRAMME -> 2.stdout -> DISPLAY
$ cat combined.txt | less => passes the output stream (what would normally be printed on the screen) of the command to left of pipe to the input stream of the command on the right; so here passing output of the file combined.txt into the less command
$ ls -lA | less => allows you (with thousands of files) to move up and down the resultant list as if the output were a normal file
$ cat combined.txt > newcombined.txt => writes the output stream of the command on the left to the file on the right
$ ls *.txt => list files in current directory that have a .txt suffix only
$ ls new*.txt => list files with text suffix that has filename starting with 'new'
$ ls * => list all files
$ ls *n* => list all files that include an 'n' (with characters on either side)
$ find . -name "*.txt" -print => another way to list specific files, and will also search all subdirectories rather than just current one
$ cd ~, then find . -name "*.txt" -print => will print every text file in home directory
$ cd ~; then find . -name *.mp3 -print > myMusic.text => creates a text document that lists every mp3 file in Music directory
$ grep binary *.txt => takes two parameters: first is search term (i.e. 'binary'; actually a regex); second is which files to search the content of for this term
$ find ~ -name "*.txt" -print | grep README => prints all text files in home directory that have 'readme' in their name: first command will find all matching files but instead of printing will redirect to grep which will only print those filenames that include 'readme'
$ find ~ -name "*" -print | grep "\d+" => looks for all files that have numbers in the filename
$ wc longtext.txt => 8 492 3003 longtext.txt; wc = word count: line, word and character count for given file
$ wc -l longtext.txt => 8 longtext.txt (lines only)
$ wc -w longtext.txt => 492 longtext.txt (words only)
$ wc -c longtext.txt => 3003 longtext.txt (characters only)
$ find ~ -name "*.txt" -print | grep README | wc -l => finds all text files; grep selects those that have 'readme' in their filename; wc -l will count how many lines were given to it by grep
$ whoami => andygout
Every file on a unix-based system has three classes of permissions:
User - determines permisions that owner of the file has; every file has a user (no more than one) as an owner
Group - determines permissions that owner of the file has; any user can belong to one or more groups of users (but doesn't have to).
Others - all users that fall into neither of above two groups
Every class has three permissions:
Read - allows a file to be read; or if a directory allows list of files to be read (reading the included files will depend on their individual read permission settings as permission are not inherited)
Write - allows you to write to a file; or if a directory allows files to be created, deleted and renamed
Execute - allows you to execute a file; such permission may be required to run a programme
$ ls l => displays directory contents in long format, with permissions on right in this format: drwxr-xr-x
First letter [d]: type of file (d = directory; - = file)
Next three characters [rwx]: read, write and execute permissions of 'user' class
Next three characters [r-x]: read, write and execute permissions of 'group' class
Next three characters [r-x]: read, write and execute permissions of 'other' class
$ chmod u+w readme.txt => change mode; u = user (g = group; o = others; a = all); + = adding permission (- = removing permission); w = write (r = read; x = execute)
$ chmod a-rx readme.txt => removes read and execute permissions from all users
Shebang is the instruction for your computer that tells what program to use to execute your script. It is a combination of a hash and an exclamation mark followed by the path to the interpreter, placed on the very first line of the file
$ cat hello.rb; then puts "Hello, world!"
To tell file where your current version of Ruby is located, add a shebang to first line of file to tell command line to use this ruby interpreter to execute the file:
#!/Users/andygout/.rvm/rubies/ruby-2.0.0-p0/bin/ruby
$ ./hello.rb => Hello, world!
Amend shebang path to work on other computers:
#!/usr/bin/env ruby
Name of the superuser is 'root'; use only as necessary as can cause significant damage to the system
$ sudo rm inaccessiblefile => superuser do; asks for your password and command will then execute with superuser priveleges (despite you not having priveleges to do so)
Can be used to make sandwiches
$ env => lists current environment variables
$ echo $HOME => /Users/andygout (displays a specified environment variable)
$ export SECRET_KEY=12345abcde => can then be acquired in Ruby code using secret_key = ENV['SECRET_KEY']
$ export SEASON=winter => creates new environment variable called SEASON
$ echo $SEASON => winter; reads back value of specified environment variable
However, in a new terminal window the environment variable will no longer exist; they must be saved to .bash_profile, one of the files executed automatically on load:
echo "export SEASON=winter" >> ~/.bash_profile
$ echo "Hello" => Hello; text is printed to the screen
$ echo "Hello, world" > hello.txt => will save short strings to a file (overwriting file's current contents)
$ echo "Hello again" >> hello.txt => will save short strings to a file (appending to file's current contents)
$ ps => see what processes have been launched (within context of terminal)
$ ps x => see all processes runnign on your computer
$ ps x | grep bash => only show bash processes running on the system
vi myfile => create new file or open existing file (using name as an argument)
i => enter 'insert' mode to insert text before cursor
o => open a new line after the current one
dd => delete current line and dozesn of others
ESC => move back to command mode
:w => tell vi to save the file (w = write); then after pressing 'Enter' the file will be written and you'll see the corresponding message
:q => quit the editor
:q! => quit the editor without saving changes
Makers Academy: Pre-course - Command Line
Vim talk with Spike (video)