5.5 Exercise: The 'which' Command

[ Team LiB ]

5.5 Exercise: The which Command The which command is available on many systems. It takes the name of an executable as a command-line argument and displays the fully qualified pathname of the corresponding executable. If the argument to which contains a path specifier (/), which just checks to see if this path corresponds to an executable. If the argument does not contain a path specifier, which uses the PATH environment variable to search directories for the corresponding executable. If which locates the executable, it prints the fully qualified path. Otherwise, which prints an message indicating that it could not find the executable in the path. Implement a which command. If no path-specifier character is given, use getenv to get the PATH environment variable. Start by creating a fully qualified path, using each component of the PATH until an appropriate file is found. Write a checkexecutable function with the following prototype. int checkexecutable(char *name); The checkexecutable function returns true if the given file is executable by the owner of the current process. Use geteuid and getegid to find the user ID and group ID of the owner of the process. Use stat to see if this user has execute privilege for this file. There are three cases to consider, depending on whether the user is the owner of the file, in the same group as the file or neither. The which command of the csh shell also checks to see if an alias is set for the command-line argument and reports that alias instead of searching for an executable. See if you can implement this feature.

[ Team LiB ]