Week 2 #

File Management #

How we survived without File Explorer

Directory Tree #

/
├── Applications
├── Library
├── System
├── *Users*
├── Volumes
├── bin
├── cores
├── *dev*
├── etc -> private/etc
├── *home* -> /System/Volumes/Data/home
├── opt
├── private
├── sbin
├── tmp -> private/tmp
├── *usr*
└── var -> private/var

Paths #

• Absolute Path: from root dir

  • eg. /Users/home/projects/course-notes/index.html

• Relative Path: from current dir

  • eg. course-notes/index.html (if current dir is /Users/home/projects/)

• Parent Directory: ..

• Directory Itself: .

  • Some commands require the dir name, . simplifies this task

Commands #

• pwd: print working directory

• cd: change directory

• ls: list

  • -a || -A: include dotfiles (. for -a, .. && . for -A)
  • -l: include more information (size, modification time, etc.)
  • -d: include only directories
  • -t: sort by modification time
  • -r: reverse order
  • -R: recursive list, whole subtree

• mkdir: make directory

• cp: copy

  • -R: recursive copy, can possibly overwrite

• mv: move

  • Can possibly replace existing files

• rmdir: remove dir

  • Precondition: the current dir is empty

• rm: remove/delete file(s)

  • -r: recursive delete, used for non-empty directories
  • No “Recycle Bin”/Trash

Core Utilities #

• cat: concatenation

  • Copy files and/or stdin to stdout
  • eg.

    $ cat file1 file2 
    ... # dumps file1
    ... # dumps file2
    $ cat file1 - file2
    ... # dumps file1
    ... # user input as stdin, use ctrl+D to exit and continue
    ... # dumps file2
    $ sort myFile | uniq | cat file1 - file2
    ... # dumps file1
    ... # dumps myFile after sorting and uniq
    ... # dumps file2
    

• head and tail:

  • head starts from start of file, tail starts from last
  • eg.

    $ head -3     # output first 3 lines
    $ head -n -3  # output all except last 3 lines
    $ tail -3     # output last 3 lines
    $ tail -n +3  # output starting from and including line 3
    

• wc: word count

  • Can count by words (-w), bytes (-c), lines (-l), characters (-m)
  • eg.

    $ wc file1
    2 6 27 file1 # 2 lines, 6 words, 27 bytes
    

• sort:

  • Sort, check if sorted, merge sorted
  • Default sort by whole-line
  • eg.

    # sample input
    Navinn CS 420
    UofT  Expensive 69
    GiveJobPls iNeedJob 180
    
    $ sort -b -k 3,3n       # sort by key=3rd field, parse 3rd field as number
    UofT Expensive 69       # lowest number
    GiveJobPls iNeedJob 180
    Navinn CS 420           # greatest number
    

• tr: translate

  • Similar to a String.replace() method

  • eg.

    $ tr 12 ab        # replace '1' with 'a', '2' with 'b'
    $ tr 1234 '[a*]'  # replace  '1','2','3','4' with 'a'
    $ tr A-Z a-z      # replace Uppercase with lowercase
    

  • -c: compliment

    • eg.

      $ tr -c 1234 '[a*]' # replace everything except '1','2','3','4' with 'a'
      

  • -s: squeeze

    • Replace consecutive occurences by a single occurrence
    • eg.

      $ tr -s 12              # can convert '11122abc211' to '12abc21'
      $ tr -s 12 abc          # replaces then squeezes
      $ tr -cs 0-9a-z ’[\n*]’ # replace everything except digits and letters with line breaks
      # then squeezes multiple line breaks -> 'one word per line'
      

  • -d: delete

    • Remove occurence
    • eg.

      $ tr -d 12    # removes '1' and 2'
      $ tr -ds 12 3 # deletes '1','2' then squeezes '3'
      

• tee: T

  • Branching out, extra pipe (T-shaped)
  • Copy stdin to stdout, and also copy to file (extra branch)
  • eg.

    sort | tee sortedfile | uniq
    # similar to sort | uniq 
    # but stdout from sort is now copied to sorted file before pipelining into uniq stdin
    

• yes:

  • Unending lines of y
  • Use case: if a program requires [y/N] a lot
  • [expletive]: outputs expletive instead of y