STUDY VAULT

Mohamed Attia
CS undergrad · visual study notes
Mohamedattiadev

Chapter 3 — Files and Navigation

11 min read

Time to study: ~90 min You will learn: how to move around the tree and how to create, copy, move, delete and read files, plus the * wildcard that makes all of them faster.

← Chapter 2 | back to Terminal 101 | next: Chapter 4 →

1. commands for navigating the file system

previously we wanted to enter the Terminal-101 dir and we explained it in human words. in order to do it in the terminal we use cd (change directory).

# we can use it step by step :
cd /
cd home
cd ati
cd Attia-Pro
cd Projects
cd Terminal-101
 
# or we can do it in one command :
cd /home/ati/Attia-Pro/Projects/Terminal-101
  • note: the / at the beginning means “start from the root”. without it, cd home means “the home folder inside where i am standing right now”, which is not the same thing.

after we go into the Terminal-101 dir we can see what is inside by using ls (list).

ls
01-command-line-basics  02-the-linux-file-system  03-files-and-navigation  README.md

let’s say we forgot where we are in the file system, we can use pwd (print working directory) to find our current path.

pwd
/home/ati/Attia-Pro/Projects/Terminal-101

now i found that i am in the wrong dir and i want to go back to the Projects dir, so i use cd ...

cd ..
pwd
/home/ati/Attia-Pro/Projects

and let’s say i want to go back more than one step, i just repeat it:

cd ../../../
pwd
/home

and if i want to go to the root dir there is a too ez command:

cd /
pwd
/

i am in the right path right now and i want to create a new directory, i can use mkdir (make directory).

cd /home/ati/Attia-Pro/Projects/Terminal-101
mkdir practice
ls
01-command-line-basics  02-the-linux-file-system  03-files-and-navigation  practice  README.md

it is created in the current dir, so always check pwd first if u are not sure where u are standing.

let’s say i wrongly created a dir with the name practise with the wrong spelling and i want to remove it, i can use rmdir (remove directory).

mkdir practise
rmdir practise
ls
01-command-line-basics  02-the-linux-file-system  03-files-and-navigation  practice  README.md
  • note: rmdir only works on an empty directory. if there is anything inside it, it will refuse:
rmdir practice
rmdir: failed to remove 'practice': Directory not empty

for that case we have rm -rf which is at the end of this section.

now i want to create a new markdown file with the name notes, i can use touch.

cd practice
touch notes.md
ls
notes.md

now i want to remove the file i created since i made it in the wrong dir, i use rm (remove).

rm notes.md
ls
(nothing, the dir is empty now)

also there is a command which i mostly use to remove a directory: rm -rf. the -r means recursive and the -f means force, so it will remove the dir and whatever is inside it.

  • this command is a very powerful one, because sometimes we have folders which contain corrupted data or files that do not want to be deleted, and with this command u can do it like a piece of cake.

  • careful: it never asks u to confirm and there is no trash bin to get it back from. always run pwd and ls before u run it, and never run it on /.

cd ..
mkdir -p old-stuff/inside
touch old-stuff/inside/file.txt
rm -rf old-stuff
ls
01-command-line-basics  02-the-linux-file-system  03-files-and-navigation  practice  README.md

now i want to copy a file into one of the dirs, we can use cp (copy).

cp README.md practice/
ls practice
README.md

u can also copy a whole directory with the -R flag, which means copy the directory and its content recursively.

cp -R practice practice-backup
ls
01-command-line-basics  02-the-linux-file-system  03-files-and-navigation  practice  practice-backup  README.md

oops, i put the file in the wrong dir, i want to move it to another dir, i can use mv (move).

mv practice/README.md practice-backup/
ls practice-backup
README.md

i added some text inside my file and i want to see it without opening a GUI editor, i can use cat.

cd practice-backup
cat README.md
# Terminal 101

a course about the terminal, written while i was learning it.

now we have another command which is similar to cat, which is less.

less README.md
# Terminal 101

a course about the terminal, written while i was learning it.
:
  • note: the difference between cat and less is that cat concatenates the file and prints it all at once in the terminal, while less opens an interactive viewer which enables u to scroll up and down to see the content. less is preferred for larger files.
  • to get out of less press q.

now i want to print the first 10 lines of the file or the last 10 lines, i can use head and tail.

head README.md
# Terminal 101

a course about the terminal, written while i was learning it.

## Chapters

1. Command Line Basics
2. The File System
3. Search
4. Permissions

tail README.md
5. Scripts and PATH
6. Input, Output and Processes
7. Text Editors

## How to study

read the chapter, then do the assignment at the end of it.
before u move to the next chapter, make sure u can do the
assignment without looking at the solution.

we can also add the -n flag which means how many lines will be printed.

head -n 3 README.md
# Terminal 101

a course about the terminal, written while i was learning it.

tail -n 3 README.md
read the chapter, then do the assignment at the end of it.
before u move to the next chapter, make sure u can do the
assignment without looking at the solution.

2. the * wildcard

everything above works on one file at a time. but most of the time u want to do the same thing to 20 files, and typing 20 names is not realistic.

so we have the wildcards. * means “anything, any number of characters”.

let’s say this is what we have:

ls
notes.md  notes.txt  old.txt  photo.jpg  readme.md

ls *.txt
notes.txt  old.txt

ls *.md
notes.md  readme.md

and it works with every command we learned above, not only ls:

cp *.txt backup/       # copy every txt file into backup
rm *.jpg               # delete every jpg file
mv *.md notes/         # move every md file into notes

now the part that matters, and it is the thing that confuses everyone including me:

the * is not a feature of ls or cp or rm. it is the shell.

before ls even starts, the shell looks at *.txt, finds the files that match, and replaces the *.txt with their names. so ls never sees a star at all. it just receives a list of file names as if u typed them by hand.

u don’t have to believe me, u can see it happen. echo just prints what it is given, so let’s give it a star:

echo *.txt
notes.txt old.txt

echo has nothing to do with files. it printed the file names because the shell had already replaced the *.txt before echo ran. that is the whole idea, and once u see it once u never forget it.

  • careful: this is also why rm * is so dangerous. u are not asking rm to be clever, the shell hands it every single file name in the folder and rm deletes all of them, exactly as told. always run ls * first to see what u are about to hit, then change ls to rm.

the other wildcards, u will use them less but u should recognize them:

  • ? matches exactly one character:
ls file?.txt
file1.txt  file2.txt

so file1.txt and file2.txt match, but file10.txt does not, because that is 2 characters where the ? allows one.

  • [...] matches one character out of a list. so [12] means “either a 1 or a 2”, not “12”:
ls file[12].txt
file1.txt  file2.txt

and now, when we get to find in Chapter 4 and it tells u to put ur pattern in quotes, u will know exactly why. the quotes stop the shell from eating the star, so that find gets to see it and use it itself.

NOTES

  1. man: it is used to show the manual of a command.

since we have learned the most important basic commands in the terminal, i want u to know also a very useful command which is man.

  • let’s say u learned all the commands above or other ones, doesn’t matter, but u did not use them for a long time so u are not able to remember all of them, which is expected. so u can use the man command which shows u the manual of a command.

  • example: u have this powerful and dangerous command rm -rf but u can not remember what the -r or the -f are, so u can check the man page of it.

man rm
RM(1)                        User Commands                       RM(1)

NAME
       rm - remove files or directories

SYNOPSIS
       rm [OPTION]... [FILE]...

DESCRIPTION
       This manual page documents the GNU version of rm. rm removes
       each specified file. By default, it does not remove directories.

OPTIONS
       -f, --force
              ignore nonexistent files and arguments, never prompt

       -r, -R, --recursive
              remove directories and their contents recursively
...

by reading this manual u can basically know what is what and remind urself of the commands. press q to get out of it, same as less.

  1. the flags:
  • u saw them already: ls -l, ls -a, ls -la. what comes after the - is the flag, and it may be a small or a big letter, they are not the same thing.
  • most commands have a short version and a long version of the same flag. ls -a is the short one and ls --all is the long one, they do exactly the same. the long one is easier to read in a script, the short one is faster to type.
  • u can stack short flags together, ls -la is the same as ls -l -a.
  • if u check the man page u will find both versions listed next to each other for every command.
  1. the path shortcuts:

these are not commands, they are shortcuts u can use anywhere u would write a path.

  • ~ means ur home dir:
cd ~
pwd
/home/ati
  • . means the current dir. u may already have seen it used by most developers when they write something like code . which basically means open vscode with the current dir.
  • .. means the parent dir, one step back. that is why cd .. works.

in Chapter 7 we will learn how to make ur own shortcuts with alias, and how to keep them forever in the .bashrc file.

  1. the positional arguments matter:

which means which argument u write first and which one u write last changes what happens.

mv notes.md ../
# or
mv file1.md file2.md ../

so we start with the file names and the directory name goes last.

  • small but important note:
mv file1.md file2.md

if we use mv with only two file names and no directory at the end, we are taking the content of file1.md and putting it in file2.md and removing file1.md. basically it is renaming file1.md to be file2.md.

Assignment

  1. Go to ur home dir using the shortcut, then print where u are to prove it.
  2. Create a dir called ch3-practice and go inside it.
  3. Create 3 files: one.txt, two.txt, three.txt.
  4. Write ur name inside one.txt and read it back without opening an editor.
  5. Rename two.txt to renamed.txt.
  6. Make a dir called backup and copy all 3 files into it using a wildcard, not by typing the 3 names.
  7. Print only the first 2 lines of one.txt.
  8. Use echo to prove to urself what *.txt expands to before the command runs.
  9. Create file1.txt, file2.txt and file10.txt, then list only the two with a single digit.
  10. Delete the whole ch3-practice dir in one command.

stuck, or done and want to check? the solutions are here

← Chapter 2 | back to Terminal 101 | next: Chapter 4 →

1 item under this folder.