LinuxBasicCommands.md

Command

• apropos

  apropos "remove files"

• whatis

  whatis rm

• man

  man man

  You can use f or b to move forward or backward and use / can be used to search for specific term and press enter to search for next occurrence.

  /browser

  q can be used to quit.

  man 7 man

  here 7 is the section which you want to look at.

• info

  info git

• help

  help if

Files

The Linux File Hierarchy Structure or the Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix-like operating systems.

• ls

  -l: vertical view

  -a: show hidden files as well

  -R: recursively go inside each directory

• file <filename>

• stat

• which tells the location of the program

• touch creates a file with the given file name

• pwdprint working directory

• cd is used to change the directory

• cp is used to copy. cp source destination. Last argument is the destination, so you can copy more than one file.

• mv is used to relocate the file/directory. Also used to rename

  mv myfile myfile2 #rename
  mv myfile2 Documents #move

• rm is to delete a file

• mkdir creates a directory(Cannot be space separated)

  mkdir my directory #creates two directory
  mkdir "my directory" #created a directory
  mkdir my\ directory2 #creates a directory

• rmdir removes the directory

• truncate is used to create files of different sizes

  truncate -s 1MB file1

• find

  find . -name apple #search if file named apple exists
  find . -name "*apple*" #search for files apple in the file name 
  find . -size -10M #files with size less than 10M
  find . -size +10M #files with size greater than 10M
  find . -name "lemon" -type d #returns only directory

  f for file, l for link, c for character device, bfor block device.

• echo takes text as input and returns it as output

  echo "krishna"

• > replaces the contents but >> appends to the file.

• | chains the commands. send the output of one command as input to other.

  ls | wc

• << Is for hearing

  wc << over
  > This so something
  > over

• stderr has code 2

  ls docs 2> errout.txt #if output is there then it saves in errout.txt
  
  find / -name "home" 2> error.txt 1> output.txt

• diff is to find the difference in two files

  diff -y file1.txt file2.txt
  diff -u file2.txt file2.txt

• cmp to compare byte by byte

  cmp file1.txt file2.txt #first difference
  cmp -l file1.txt file2.txt #all difference

• hexdump

glob

• * zero or more character
• ? one character

nano

• ctrl + e end of line
• ctrl + a start of the line
• ctrl + j to justify
• M is esc
• ^ is shift
• ctrl + _ to go to a line number
• ctrl + k to cut
• ctrl + u to paste

Vim

Two modes: command and insert

Command modes takes key strokes as command and insert mode let you type in a document.

i is used to go to insert mode. esc to go back to command mode.

:w to save

:q to quit

In command mode use / and then text to search.

Use ^ to move to the beginning of a line and $ to move to the end.

Links

• Hard link and Soft(symbolic) links
• Hard link point to inode (address).
• Soft link points to the file name(renaming breaks the soft link)

ln -s /home/krishna/users.txt Documents/user-list.txt

ln is for link, -s is for symbolic and then full absolute path and then destination. Relative path will is not used a system will use the relative path from where the sym link is, so it will point to users.txt in Documents

Hard Link:

ln /home/krishna/users.txt Documents/list.txt

Archives

Archives: combines files into one file

Compression: reduce the size of a file

• tar: Tape Archive

  Does linear scanning

  tar -cf docs_archive.tar * 

  -c is for create

  -f is to tell that it should redirect the output to a file

  * here tells that archive all the files

  List all the files in a archive

  tar -tf docs_archive.tar

  -t is for tar

  Unpack

  tar -xf docs_archive.tar -C extract_folder

  -x to extract

• Gzip and Bzip

  tar -czf files.tgz file*.txt text*

  -z is for Gzip

  -j is for Bzip

• zip

  zip myfiles.zip *
  unzip myfiles.zip -d unzipped #-d to specify a folder

Regex

• z{2} search for zz

• \. search for .

• ^ beginning of line $ end of line

  cat users.txt  | grep -E ".*"
  cat users.txt  | grep -E "a"
  cat users.txt  | grep -E "[Aa]"
  cat users.txt  | grep -E "[A-M][a-g]"

• sed: stream editor

  cat users.txt | sed 's/e/d/' #s is for substitute (replace the first `e` with `d`)
  
  cat users.txt | sed 's/e/d/g' #`s` is for substitute (replace all `e` with `d`) and `g` is for greedy
  
  cat users.txt | sed 's/[A-Ea-e]/_/g'
  
  cat users.txt | sed 's/\ *//g' #gets the first name

• awkis for reformatting

  cat users.txt | awk '{print $2}' #print item 2
  cat users.txt | awk '{print $2 ", " $1}' #print item 2 , item 1
  cat users.txt | awk '{print $2 ", " $1}' | sort

SSH

sudo apt install openssh-server
ip a #to check ip address
ssh user@ip

File transfer

• SFTP: SSH File Transfer Protocol

  sftp user@ip
  get file3 #to download
  put fil3 # to upload

• SCP: Secure Copy Protocol

  scp user@ip:<location_file> . #download
  scp file4 user@ip:<location>  #upload