List of shell script special variables

Author：rab

A thousand times , You can have a look at what you haven't remembered yet , Passers by can also take a glance , These are a few shell Can you distinguish the special variables of the script ？

Be careful ️️️

Notice here $* and [email protected] The difference between , Without double quotation marks （" "） Under the circumstances , The two values are exactly the same , But with double quotation marks , We need to pay attention to ：

• No double quotes ： There's no difference between the two , It's all about "$1" "$2" ... "$n" Format output .

  #  for example 
  sh hello.sh aa bb cc
  
  # $*  and  [email protected]  Output 
  $*：aa bb cc
  [email protected]：aa bb cc
  

• There are double quotation marks ： There is a difference between the two ,"$*" The output format is "$1 $2 ... $n", That is, an overall output ."[email protected]" The output format remains the same as when there are no double quotes .

  #  for example 
  sh hello.sh aa bb cc
  
  # $*  and  [email protected]  Output （ It looks the same , however "$*" The value of is a whole , That is to say aa bb cc Is a value with spaces , and "[email protected]" Are three independent values separated by spaces ）
  "$*"：aa bb cc
  "[email protected]"：aa bb cc
  
  ================================
  #  If you use one  for  Loop to get the value 
  for i in "$*"
  do
      echo $i
  done
  for i in "[email protected]"
  do
      echo $i
  done
  
  # $*  and  [email protected]  Output （"$*" Only one cycle , Because it has only one value , and "[email protected]" But it has been cycled three times , Because it has three values ）
  "$*"：aa bb cc
  "[email protected]"：
      aa 
      bb 
      cc
  

complete ！