UNIX Shell For Dummies

Learning a few UNIX commands can be useful. Since it’s the ‘default’ programming language that pops up when you run the Terminal, it’s worth knowing a few of the more basic commands: These are sorted by ‘difficulty’ - you should know the first ones first.

Navigation

cd - changes the current directory.

• cd ~ - changes where you are to HOME directory
• cd Documents - goes one file deeper into the ‘Documents’ folder
• cd .. - goes up one directory

ls - list files or directories in current directory

• ls -la - uses the options ‘-l’ (list in detail) and ‘-a’ (show hidden files)

pwd - print working directory. Shows where you are (relative to the root folder)

Copying

cp - copy

• cp anchovy.txt fishes/anchovy.txt - creates a copy of the file under the ‘fishes’ directory.

cp -r - copy recursively. Useful for directories.

• cp -r anchovy fishes/anchovy - copies all the anchovy-related files from the folder ‘anchovy’

Deleting

rm - remove

• rm platypus.txt - deletes the specified file

rmdir - remove directory

Moving / Renaming

mv - move

• This works like cp, except it removes the initial file / directory
• mv anchovy.txt fishes/anchovy.txt - moves & removes the file.
• Renaming: mv anchovy.txt sardine.txt

Creating Folders

mkdir - creates a new directory

• mkdir pelicans

mkdir -p - creates a series of new directories.

• mkdir -p Pelecanidae/Pelicans/Great-White-Pelican

Getting help

man - find the manual

• man man
• man pwd

Showing files

cat - show pure text version of the file.

• Concatenates & prints the file cat gerbil_name.txt - simply outputs text: ‘Fred’

less - outputs text with more features.

• Better for larger files. Includes scrolling, searching, etc..
• less encyclopedia.txt - won’t crash & is still useful

sort - guess what this one does…

• Go on. Guess. I’m not going to tell you.

Comparing files

diff - shows the differences between two files

• diff red_spotted_woodpecker.txt lesser_woodpecker.txt

Finding programs

whereis

• Useful if you’re running the wrong version of ruby. Or something similar.
• Provides the location of the executable file.

Changing File Permissions

chmod

• A common chmod file permission to set is chmod 755, which is rwx for the Owner but only rw for other users.

Search for text

grep

I’ve written a quick primer on UNIX file permissions here

Grep’s a fairly big topic:

• grep "some string" filename
• grep "REGEX" filename
• grep -i "some string" filename - case insensitive

Flags

Flags are optional parameters that you can pass in to a shell command. We’ve met some already; here’re two: ls -la. You can see a full list of available options under the man page of the commands.

Tags

shell unix bash