Part 2: Introduction to Linux Commands

Overview of Common linux shell commands

• Different types of shells
  • sh: Bourne shell
  • ksh: Korn shell
  • tcsh: Tenex C shell
  • zsh: Z shell
  • fish: Friendly Interactive shell
  • bash: Bourne again shell
• To check which shell you are using
  • $ echo "$SHELL"
  • $ printenv SHELL

Shell Command Applications

1. Getting information
   • $ whoami: username
   • $ id: user ID and group ID
   • $ uname: os name
     • $ uname -a: prints the system info in the following order: Kernel name, network node hostname, kernel release date, kernel version, machine hardware name, hardware platform, os
   • $ ps: running processes
   • $ top: resource usage
   • $ df: mounted file systems
     • $ df -h: available disk space in a ‘human readable’ format
   • $ man: reference manual
   • $ date: today’s date
2. Working with files
   • $ cp: copy file
   • $ mv: change file name or path
   • $ rm: remove file
   • $ touch: create empty file, update file timestamp
   • $ chmod: change/modify file permissions
   • $ wc: get count of lines, words, characters in file
   • $ grep: return lines in file matching pattern
3. Navigating and working with directories
   • $ ls: lists files and directories
   • $ find: find files in directory tree
   • $ pwd: get present working directory
   • $ mkdir: make directory
   • $ cd: change directory
   • $ rmdir: remove directory
4. Printing file and string contents
   • $ cat: print file contents
   • $ more: print file contents page by page
   • $ head: print first N lines of file
   • $ tail: print last N lines of file
   • $ echo: print string or variable value
     • $ echo -e: when working with special characters
5. Compression and archiving
   • $ tar: archive a set of files
   • $ zip: compress a set of files
   • $ unzip: extract files from a compressed zip archive
6. Performing network operations
   • $ hostname: print hostname
   • $ ping: send packets to URL and print response
   • $ ifconfig: display or configure system network interfaces
   • $ curl: display content of file at a URL
   • $ wget: download file from URl

7. Monitoring performance and status

8. Running batch jobs

Item Navigation

• Viewing your file all at once
  • $ cat <file_name>(catenate) - print entire file contents
  • $ more <file_name> - Print file contents page by page
    • the content which is displayed in the output varies according the dimensions of terminal eg. if you increase the length then the content will increase
    • clicking on spacebar will change the next part of content
    • q + enter will help you to return to cmd
  • $ head <file_name> - Print first 10 lines of file
    • $ head -n 3 <file_name> - first 3 lines
  • $ tail <file_name> - print last 10 lines
  • $ wc(word count) - lines, words, characters(counts new line a character)
    • $ wc -l <file_name> - displays the total lines
    • $ wc -w <file_name> - displays the total words
    • $ wc -c <file_name> - displays the total characters

Customizing view of file content

• Sorting your views line by line
  • $ sort - sort lines in a file
    • $ sort -r - reversed order
• Excluding repeated lines from views
  • $ uniq - filter out repeated lines (only when they are consecutive)
• Extracting lines matching a pattern
  • $ grep(global regular expression print) - Return lines in file matching pattern
    • $ grep -i - makes it case insenstive
• Extracting slices from lines
  • $ cut -c 2-9 <file_name> - displays from character 2 till 9 for all the new lines
  • $ cut -d ' ' -f2 <file_name> - displays the second field for each line
• Merging lines from multiple files
  • $ paste <file1> <file2> <file3> - merge lines from different files
  • $ paste -d "," <file1> <file2> <file3> - delimiter “,” will display the result by separating with the help of comma

File Archiving and Compression Commands

• $ tar -cf <name_given>.tar <name_of_directory> - Tape Archiver - Archive and Extract files
  • Compressed .tar file - tar -czf <name_given>.tar.gz <name_of_directory>
  • $ tar -tf <name_given>.tar - List archive contents
  • $ tar -xf <name_given>.tar <name_of_directory> - extract files and folders
• $ zip <name_given>.zip <directory_to_zip> - Compress files and directories to an archive
  • $ unzip <name_given>.zip - Extract and decompress zipped archive

Networking Commands

• Machine’s host name
  • $ hostname - print the host name
  • $ hostname -i - ip address of the hostname
• Getting network information
  • $ ifconfig - Interface configuration - Display or configure the system network interfaces
  • $ ifconfig eth0 - information about the ethernet adapter
• Testing server connections
  • $ ping - send ICMP(Internet Control Message Protocol) packets to URL and print response
  • ping -c 5 www.google.com - return 5 ping results, aborts and then displays the results
• Web scraping with curl
  • $ curl <client_url> - Transfer data to and from URL
  • $ curl www.google.com -o google.txt - saves the content to google.txt file
• Downloading files from URL
  • $ wget - Web get - Downloading file(s) from a URL
    • has recursive downloading capabilities.

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Have Fun …