Working with Files and Directories

Creating Files and Directories: touch, mkdir

Making Directories (mkdir)

create folder to practice in
from home use the command

mkdir Linux_Practice

move to the folder

cd Linux_Practice

Creating Nested Directories

create a full folder structure

Project
    Images
    Docs
    Source

instead of creating each fold individually use the -p (parent) flag
command creates parent folder(s)

mkdir -p Project/Images/HighRes

note relative path

Creating Files (touch)

fastest way to create a blank, empty file is to use the touch command

touch document.txt

command created to update file's timestamp
when an existing file is touched, its timestamp is updated
if file doesn't exist it will be created

use touch to create the following files to work with

report_january.txt
report_february.txt
photo.jpg
audio.mp3

create a folder as well

mkdir Archives

Copying, Moving, and Renaming: cp, mv

Copying Files (cp)

cp command creates a duplicate file

cp <source> <destination>

copy a file

cp report_january.txt report_january_backup.txt

Copying to a Directory

forward slash at end indicates a directory

cp photo.jpg Archives/

The Recursive Copy

to copy a folder use the -r (recursive) flag

cp -r Project Archvies/

Moving Files (mv)

to move a file use the mv command

mv audio.mp3 Archives/

Renaming Files (The Secret of mv)

no rename command in Linux
treated as move
moving file from one name to another

mv report_february.txt final_report.txt

Safety Warning : Silent Overwrites

when copying or moving a file, if the file already exists it will be overwritten
to prevent this use the -i flag

mv -i report_february.txt final_report.txt

system will prompt

cp: overwrite 'final_report.txt'?

Deleting Files and Directories: rm, rmdir

Removing Empty Directories (rmdir)

create temporary folder before deleting it

mkdir TempFolder
rmdir TempFolder

as a safety feature rmdironly removes empty directories

mkdir FullFolder
touch FullFolder/file.txt
rmdir FullFolder

output

rmdir: failed to remove 'FullFolder': Directory not empty

Removing Files (rm)

to delete a file use the command

rm report_january_backup.txt

no confirmation or response
the file is just gone

The Nuclear Option: rm -tf

to delete a populated folder use the recursive -r command

rm -r FullFolder

if a file is write-protected the command will prompt for confirmation
to bypass all checks and confirmations use the force -f flag

rm -rf FullFolder

quietly deletes everything

Understanding File Types: Regular Files, Directories, Links, and Special Files

Linux ignores file extensions
can name a text file 'textfile.jpg' and it will be treated as a text file
can be opened in a text editor
can use the file command to determine what the file is

file textfile.jpg
textfile.jpg: empty

running the command against a real image

image.jpg: JPEG image data, JFIF standard 1.01, resolution (DPI), ...

Links: Hard vs Soft

a soft link aka symbolic link/symlink is like a Windows' shortcut
a special file which points to another file
if original file is deleted, the link is broken
the command structure to creat a symlink is

ln -s <target file> <link name>

create a symlink

ln -s final_report.txt link_to_report

listing the folder contents with ls -l

lrwxrwxrwx 1 n4jvp n4jvp   16 Jan  1 18:01 link_to_report.txt -> final_report.txt

the permission string starts with a l indicating the file is a link
if link_to_report.txt is edited, final_report.txt is actually being edited

a hard link is not a shortcut
a hard link is like a named pointer to a file
if a hard link to textfile.txt is tf.txt, both names point to the same file
if textfile.txt is deleted the data is still there and can be accessed via tf.txt
data is only deleted when all hard links are deleted
hard links are rarely used

Working with Hidden Files and Directories

to hide a file simply start the filename wiith a dot (.)

touch .secret_file

the ls command will not show the file
the ls -a command will show the file

Why Use Hidden Files?

used mostly for configuration files
files are hidden to view clean

Finding Files: find, locate, which, whereis

Quick Search: locate

locate is the fastest way to locate a file
does not search hard drives
searches a database (index) of all files on the system
to locate every file with a .jpg extension

locate .jpg

the database is updated once a day
newly created files may not appear in the list
an update can be forced using the command

sudo updatedb

takes time to update database

Note : here the system responded with

Command 'locate' not found, but can be installed with:
sudo apt install plocate

during the install it was determined the llvmll19 package is no longer required
the package can be removed by using the command

sudo apt autoremove

Deep Search: find

find searches the hard drive in real time
the syntax

find <where to look> <criteria> <what to search for>

to find a specific file

find . audio.mp3

the dot represents the current folder
search is case-sensitive

for a case-insensitive search use the -iname flag

find . -iname audio.mp3

to find all files in home directory (~) which are larger than 10 Megabytes

find ~ -size +10M

to find only directories with the same name

find . -type d -name "<directory name>"

to find all directories from home

find ~ -type d

to find all files with names ending in .tmp and delete them
this is dangerous

find . -name "*.tmp" -delete

Finding Programs: which

need to consider hows/whys of this
quote from the text

Sometimes you type a command like python, and you want to know exactly which file is being executed. 
Type: 
    which python3
 Output: 
    /usr/bin/python3 
This tells you the absolute path of the executable.
If which returns nothing, the program is not installed or not in your PATH.

Manual Finder: whereis

command returns where the binary is, where the source code is, and where the manual page is

whereis ls

output

ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

File Globbing and Wildcards: *, ?, []

selecting multiple files as a group
use wildcards aka Globbering

Asterisk (*)

matches zero or more characters

Question Mark (?)

matches exactly one character

Square Brackets ([])

specify a range or list of characters
case-sensitive

list : file[123].txt matches file1.txt, file2.txt, file3.txt
range : Image_[A-Z].jpg matches Image_A.jpg, Image_B.jpg ...

Wildcard Warning

always check the command line multiple times when using rm command
especially neded when using wildcards

Best Practices for File Organization

Home Directory is Sacred

do not anything direcly in the home directory
awlays put files in subdirectories

No Spaces in Filenames

use an underscore or hyphen instead of spaces

Use ISO Dates

use YYYY-MM-DD format
ISO dates sorts properly and consistantly

Logically Hierarchy

organize files using subfolders
manage number of files in a folder

Summary

mkdir -p : create nested directories
touch : update a timestamp or create an empty file
cp -r : recursive copy, for copying directories
mv : move or rename files
rm : deletes diles permanently
rm -rf : forces recursive delete of everything, dangerous
file extensions : only have meaning to users
hidden files : any fiename start with the dot operator is hidden
find : search tool for files and directories
wildcards : as named