which
Locate a program file in the user's path
SYNTAX
      which command ...
Display the command that will be executed by the shell after substitutions, path searching, etc.
The builtin command is just like which(1), but it correctly reports 
  tcsh aliases and builtins and is 10 to 100 times faster.
  
  "God shows his contempt for wealth by the kind of person he 
  selects to receive it" - Austin 
  O'Malley
Related commands:
  
  find - Search for files that meet a desired criteria
  grep - Search file(s) for lines that match a given pattern 
  
  ls - List information about file(s) 
  locate - Find files
  where - Report all known instances of a command
  
  Equivalent BASH command:
 
  which - Locate a program file in the user's 
path.