linux-commands-part-1-4.md

Linux Commands Part 1 - 4

Tags: linux-com-book

Introductory Commands

• # before terminal means super-user

• date to print date and time

  • Sat Jun 18 12:01:17 AM IST 2022

• cal to print calendar

• df to print disk drive and usage

• free to print memory

• pwd print working directory

• Absolute PathName : begins with root directory and follows the tree branch by branch till the desired folder

• Relative PathName : starts from the working directory

• cd to change directory

  • cd - to revert to previous directory
  • cd ~username : to change directory to another user

• ls : to list directories

  • ls directory_1 directory_2 : to print list or multiple directories

  ➜  ~ ls programm software
  programm:
  azure-dev-hackathon  inbox-app            
  configs              learning-springboot  
  demo                 playground           
  
  software:
  jetbrains-toolbox  tor-browser_en-US

  • ls -l : for more details
  • ls -lt : to list sorted acc. date modifed
    • —reverse : to reverse the sort

  

Long Listing Details

• file filename : to print a brief description of the file’s contents
• less : to view content of file

File Structure

Symbolic Links | Soft Link | Symlink

• symbolic links are like aliases or another name for the file

lrwxrwxrwx 1 root root
11 2018-08-11 07:34 libc.so.6 ***->*** libc-2.6.so

Why they are useful ?

• Imagine we have a file with name foo . Whenever we update it we, change its name to foo-date-time, but the programs/user referencing it wouldst know that the name has change. To tackle this problem, we create a symlink of file foo → foo-date-time and the programs/user user only reference the symlink.
• So even if we change the name of file foo, it wont affect the programs as they would be referencing the symlink.

Manipulating Files and Directories

• to create new directories
  • mkdir dir_name
• to create multiple directories
  • mkdir dir1 dir2 dir3
• to copy file to another directory
  • cp item directory
  • if cp item1 item2 then content of item2 is replace with item1
• use -a file while copying to copy the attributes as well

• The mv command performs both file moving and file renaming, depending on how it is used
• to move item to another directory mv item... directory
• to delete item rm item

Hard Links vs Soft Links

Hard Link

• Hard links are the original Unix way of creating links
• Every file has a single hard link that gives the file its name
• Limitations
  • A hard link cannot reference a file outside its own file system
  • A hard link may not reference a directory
• A hard link is indistinguishable from the file itself

// for hard link
-> ln file.txt link

-> ls
-rw-r--r--. 1 udayyadav udayyadav  12 Jun 20 23:06 file.txt
-rw-r--r--. 2 udayyadav udayyadav  12 Jun 20 23:06 link1

Soft Link

• They work by creating a special type of file that contains a text pointer to the referenced file or directory
• They are like windows shortcuts
• If file is deleted, then link points to nothing, it is broken

// for soft link
-> ln -s file.txt link

-> ls
lrwxrwxrwx. 1 udayyadav udayyadav   9 Jun 21 07:59 link2 -> file2.txt

WildCards