You can use command which (use to locate a command). which returns the pathnames of the files which would be executed in the current environment, had its arguments been given as commands in a strictly POSIX-conformant shell. It does this by searching the PATH for executable files matching the names of the arguments.

Syntax:
which {command-name}

Examples:

$ which ls

/bin/ls

$ which gcc

/usr/bin/gcc

See also:

• How Linux or UNIX Understand which program to run – PART I and II