Bash Tips

Basics

• cd

  cd - go back to last directory

• ls

  • ls -a list everything include hidden files
  • ls -aF and label the folders or execution files

• cp

  • cp x y copy a file x and rename it as y
  • cp x y z folder_path copy file x, y, z into a folder
  • cp -i x folder_path copy file and ask overwrite or not if it's exist
  • cp -r folder1_path folder2_path copy a folder into another folder (r means recursive)
  • cp -v ... give us a verbose info

• cat

  • cat n x show content of x with line number
  • cat x y z show content of x y z one by one

• more x / less x

  more x to show content of x and start from beginning; less x to show content of x in an screen and quit without anything leave

• touch

  can modify the last edited time of one exist file

  • touch -c blabla just touch one file only it exists

• mkdir

  • mkdir -p new_parent_folder/new_child_folder create both new_parent_folder and new_child_folder

• wild card

  • * means any charactors
  • ? means any single charactor
  • [abc] means a or b or c
  • [!abc] means any charactor that is not a, b or c
  • [[:alpha:]] means only (one) letter; [[:digit:]] means only (one) number; [[:lower:]] means only (one) lowercase letter; [[:upper:]] means only (one) uppercase letter;

• variables

  how to set / unset variables in shell?

  # mind that there is no spaces!
  name=evan
  
  # unset
  unset name

  how to get value of variables?

  ${name}

  how to get variables length?

  ${#name}

  how to get part of variables?

  # from the second one to the end
  ${name:2} 
  
  # from the second one, and the length is 1
  ${name:2:1}
  
  # from the last third one to the end
  # mind the space
  ${name: -3}
  
  # from the last third one, and the length is 2
  # mind the space
  ${name: -3:2}

  how to get rid of specific charactor from a variables?

  • start operator # and end operator %

  only matched charactors will be removed

  # get rid of 'e' from 'evan'
  # if this charactor doesn't exist, then do nothing
  ${name#e}
  
  # you can also get rid of multiples charactors like 'ev'
  ${name#ev}
  
  # remove everything before some charactors(included)
  ${name#*v} 
  
  # remove everything after some charactors(included)
  ${name%v*}