The path

• in CIS department, controlled w/ 'subscribe' program, but this will not work for bash
• a list colon-separated of directories to search to find which program to run when you enter a command
• what does the path look like? echo $PATH

• type emacs
      export TEMP=$PATH
      export PATH=
      type emacs
      ls
      type ls
      type cd
      export PATH=/usr/bin
      type emacs #its been found
      type ls #still not found
      for FILE in /bin/* ; do  echo "$FILE"; done 
       #emulate ls
      export PATH=/bin/:$PATH
      type ls #now we found it
      export PATH=$TEMP #get our old path back
      export PATH=${HOME}/usr/bin:$PATH 
      #for your own executables
  

• why do echo and cd work? They are built in shell commands, as type tells us: type cd; type echo; type type
• type is similar to 'which', but which should not be used in bash because it won't always return the correct answer: on cis dept computers, in bash "type time; which time;"
• The current directory '.'
  • Sometimes, if you want to run a program in the current 'working' directory, you have to run it like this: ./myprogram
  • echo $PATH #do we see :.:? this can be bad, but it makes some things easier.
  • why it might be bad: If someone keeps a program called 'ls' in their home directory, and if you have '.' in your path, cd  evilMan;ls might execute THEIR version of ls. If they are evil, this can be bad!
  • on the other hand, it makes people who are ignorant of the PATH variable happy, because they can run their programs without saying './myGoodProgram'.

  • #BUT it still might not help, you should always
    #run programs in the current directory with the
    # "./" notation
    export $PATH=$PATH:.
    mkdir temp
    cd temp;ls
    emacs -nw -q helloWorld.c
      #C program:
      #include <stdio.h>
      int main() {
       printf ("Hello, World.\n");
       return 0;
      }
      C-x C-c ;to exit emacs
    gcc helloWorld.c -otest
    test #why doesn't my program do anything!?
    echo $PATH #dot is in my path
    type test 
    #oops, test is built in!, it'll get run first
    ./test 
    which test
    

  • one thing to note here is not to name your program 'test', or on some systems, you shouldn't name your program a.out this is a common mistake.
  • The big lesson: don't put '.' in your path, use the "./" notation instead.
• (also works on tcsh)