os_commands.txt

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                           BASIC LINUX COMMANDS
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ls=   listing files and directories.

man=  manual( man ls,man cd,man pewd,man touch)

touch=(--> to create a file by putting command like = touch a.txt
       --> to create multiple files =touch b.txt c.txt
       --> also used to modify timestamps
       --> enter man touch to know all use of touch like-a,-c,-f,-m and to return back press q )

cat=  (--> create and write file : cat > ABC.txt  . enter likre "hello" To exit press ctrl+d or ctrl+z
       --> read the content of file : cat ABC.txt
       --> append content into file : cat >> ABC.txt then enter "here you go".Now the line will give u "hello""here you go"
           the reason for the use of >> instead of > is because >> will not overwrite
       --> concatination: cat >> b.txt a.txt c.txt here b.txt is destination file where a and b contents are concatinated )

cp=   (--> cp a.txt ABC.txt : this will give the only the first line of the file )

mv=   (--> it will move + cut + rename + paste
       --> mv ABC.txt XYZ.txt)

mkdir=(--> used to create directories
       --> mkdir -p ABC -> single dirctory is created  [to check enter ls then enter cd to know its path]
       --> mkdir -p ABC/DEF/GHI : inside ABC there is DEF  and inside DEF there is GHI [then put cd ABC then ls we get DEF]
       --> mkdir -p AB/{A,B,C} : there are 3 different directories created in AB then to see result enter cd AB)
      
rmdir=(used to remove empty directories )
      
rm =  (used to remove files and non empty directories
      --> rm -f ABC [to remove files or we can use rm abc.txt after thet enter y for yes or n for no]
      --> rm -r DFG [remove files + directories]
      --> rm -d SRE [remove empty diretory]  )

chmod =( to change the permissions of file/directories
         --> chmod u=rwx,g=w,o=rwx abc.txt [ first enter ls -l ] 
         --> if u dont want to give permission then do chmod u=,g=,o= abc.txt )

cd    =   ( to change the directory )

pwd   =  ( present working directory: pwd )

ls -a =hidden files
ls -A =almost all the file(except for parent file and current file)
ls-l  = long list(if starting is d then directory,size in kb but not displayed)
ls-lh = long listing but size is in human readable form (size will be displayed)
ls -r = list in reverse order
ls-R  =list directory contents recursively
ls-s  =listing the size of all files and directories
ls-s  =(will display file with highest file first)