Linux Useful utils

• Which Shell are you running?

  • Execute the command echo $0

• Aborting and suspending the execution of linux programs

  • Control-Z suspends the program
  • Control-C aborts the program

• Redirecting output of a command to a file instead of terminal (stdout)

  • command > file
  • Eg: ping -c 4 google.com > pingresults.txt
  • If you want to append the text to existing file use >>
  • Eg: ping -c 10 google.com >> pingresults.txt

• Redirecting input can be done using < eg: head < /proc/cpuinfo

• Common Errors

  • NO Such file or directory
  • file exists
  • Not a Directory, Is a directory
  • NO space left of device
  • Permission Denied

• What is softlink (symbolic link) in linux and what is hardlink?

  • Softlink(symbolic) is an actual link to original file whereas hard link is a mirror copy of original file.
  • If you delete the original file, soft link has no value (since t whatever file it points no longer exists)
  • If you delete the original file, hard link will still has the data of the original file
  • Softlink
    • Can cross the file systems
    • Allows yo to link between directories
    • permissions will not be updated
    • has only the path to original file not contents
  • Hard link
    • Can’t cross file system boundaries (it exist on same filesystem)
    • can’t link directories
    • permissions will be updated if we change the source
    • It has contents of original file
  • Create a Symlink or softlink
  • Create a hardlink
  • What will be difference between hard link and normally copied file?

• Identifying Commands

  • type: Type is a shell builtin command which displays the kind of command once you give a particular command

  type ls
  type cp
  type ping
  type type
  

  

  • which-Display an Executable location

  which ls
  

  

• Getting a Commands Documentation

  • help: bash has a built-in help facility for each of the shell builtins.

  help cd
  

  • –help: Many executable programs support a –help option displays the description of commands

  mkdir --help
  

  • man: Most executable programs intended for command line usage will provide manual

  man <command>
  man ls
  

  • apropos-Display appropriate commands

  apropos partition
  

  • info command: This commadn will show mauals with hyperlinked much like web docs

Pipelines

• Is a capability of commands to read output of command as input to other command
• Generally operator | is referred as pipe

command1 | command2

• Pipelines are often used to perform complex operations on data. It is possible for you to put several commands together into a pipeline

 ls -al /bin /usr/bin | sort | less
 ls -al /bin /usr/bin/ | sort | uniq | wc -l

tee

• tee command will read from stdin and send the output to stdout and files

ls -al /bin /usr/bin | tee ls.txt | sort | uniq | wc -l