Monday, July 4, 2011

Difference between $x and ${x}

   Many times in shell scripts we would have witnessed two different forms of notations being used against variables: $x and ${x}.  Are they both same or is there any difference between them? Let us discuss in this article:

Let us assign a value to the variable, x:
$ x=10

Now, lets try to display the value using both the above notations:
$ echo $x
Displaying using the second notation:
$ echo ${x}
  As seen above, it does not look like there is any difference. But it is not so. The actual difference we will see now:

Let us try to join or concatenate the literal "y" along with the value of $x:
$ echo $xy
   Nothing got printed for "echo $xy".  Now, let us the second notation to display:
$ echo ${x}y
  What happened? When we said $xy, the shell interpreted it as being asked to print the value of a variable named "xy". Since there is no such variable "xy" being defined, a blank output. However, the second notation ${x}y is being interpreted as : print the value of x and concatenate it with the literal "y", and hence the result "10y".


  1. There's no difference between $x and ${x}. There *is* a difference between $xy and ${x}y, which is something entirely different.

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