Intro to Linux

• / (root), /home, /tmp
• Where am I? pwd
• Moving around cd
• Full vs relative path names
• Making directories mkdir, and removing them rmdir

• What files do I have? ls
• Command options: ls -l, ls -a
• Manual: man ls, man man
• The pager: less
• Make a file: touch
• Delete a file: rm

Send output to file (overwriting it if it already exists)

date > testfile.txt

Append output to file

date >> testfile.txt

Get input from one file and send output to another file

wc < testfile.txt > otherfile.txt

Get input from one file and send output to another command

cat < testfile.txt | wc

• Who is logged in?

  w
  

  (you might have to stop this with Control-C)

• Who were the last eight people to log in?

  last | head -8
  

• Some fun

  cowsay "It's fun to learn Linux"
  

• From the command line
  • Python
  • Ipython
  • Racket

• Download this python program and this racket program from the command line

wget https://advprog.auc-computing.nl/code/chars_per_line.py
wget https://advprog.auc-computing.nl/code/sum-ints.rkt

#!/usr/bin/env python3
# -*- mode: python; coding: utf-8; -*-

"""
Read line by line and write the number of characters in each line.
"""

import sys


def main():
    for line in sys.stdin:
        print(len(line) - 1)  # excluding newline character


if __name__ == "__main__":
    main()

#! /usr/bin/env racket
#lang racket/base

;; Read numbers from standard input, one per line. Print their sum.

(define (main)
  (for/fold
      ((total 0))
      ((line (in-lines)))
    (+ total (string->number line))))

(main)

• Change the attributes of the files to make them executable

chmod +x chars_per_line.py
chmod +x sum-ints.rkt

• Run them from the command line. Finish with Control-d

$ ./chars_per_line.py
abc
3
defg
4
h
1
$ ./chars_per_line.py < chars_per_line.py
21
38
0
3
66
3
0
10
0
11
26
56
0
26
10
$

$ ./sum-ints.rkt
1
2
3
6
$

• Now combine them using redirection and a pipe

$ cat chars_per_line.py | ./chars_per_line.py | ./sum-ints.rkt
270
$

• When looking for executables, Linux checks the directories in the $PATH environment variable

echo $PATH

• LinuxCommand
• The Command Line Crash Course
• The bash shell and command language
• bash guide

• More shell, less egg

  Read a file of text, determine the n most frequently used words, and print out a sorted list of those words along with their frequencies.

  McIlroy's shell script

  #!/bin/bash
  
  tr -cs A-Za-z '\n'|
  tr A-Z a-z |
  sort |
  uniq -c |
  sort -rn |
  awk '{print $2}'|
  head -n $1