Lecture 1

Linux Shell

Shell: Interface to the OS

• gets OS to do stuff - run programs, manage files

• graphical shell (Windows, Mac OS, Ubuntu)

• command line (type commands - terminal)

In this course, we use Bash.

# type this to ensure you are in bash
$ echo $0
>> -bash

Files, Input/Output

$ cat

• Displays contents of root directory

• First slash denotes root directory (top of directory hierarchy)

$ cat /path/to/file

What if I just run :

• Copies output

• Is this useful?

  • Can capture output and put in a file -cat > output.txt

# Example
$ cat
hello
>> hello
hi
>> hi

Stopping cat from running: Ctrl+D

Text in Linux

In linux, every line in valid txt file must end with a newline character.

• Marmoset checks that last line ends in

• When printing output, should end in

Terminating program

• For infinite loop or crash, to terminate program: Ctrl+C

$ ls

• Displays file in current dir

$ ls -a

• Displays hidden files + files in current dir

$ pwd

• prints the current dir

• stands for present working directory

Redirecting Output

• output redirection symbol: >

• what would be printed to output, send to file

# Example:
$ cat args > file

Redirecting Input

• input redirection symbol: <

# Example:
$ cat < inputfile

• reads intput from file instead of keyboard

• in the case of $ cat, the output is the same

Difference in Behaviour

• $ cat /file -> pass "file" as an argument to cat which opens the file and prints it

• $ cat < file -> the shell opens the file and passes its content in place of keyboard input

$ wc

• line count, word count, character count

Asterisk in Linux (*)

• *.txt is a globbing pattern

• asterisk means match anything

• when shell sees globbing pattern, the shell expands globbing pattern to match non-hidden files

• More globbing patterns on reference sheet

• Many commands can accept arguments or input with the exception of $ echo

# Example:
## Copies input.txt into output.txt
$ cat < input.txt > output.txt

# Example:
## Prints output preceeded by line numbers
$ cat -n < input.txt > output.txt