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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

    List of options of ls command

Long Listing Details

details of fields printing long list

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

File Structure

Linux file structure part 1

Linux file structure part 2

Linux file structure part 3

Linux file structure part 4

Linux file structure part 5

  • 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

options for cp command

  • 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

options for rm command

  • 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
  • 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

different wildcards present

matching with different characters

wildcard example