COM584 Class Test #1 Week #3 Notes

COM584 Class Test #1 Week #3 Notes

1. File Permissions

   • Notations
     • Symbolic: Uses criteria such as categories and operators to change file permissions.
       • Example: chmod u+x file4
     • Numeric: Uses numbers from 0-7 to represent file permissions.
       • Example: chmod 774 file4

2. Shell Scripts

   • Compiler: A program that translate source code into executable program.
   • Interpreters: Accepts and parses instruction, the converts into executable instructions, then executes.
   • Variables
     • Environment: A placeholder for data that can change - gets its value automatically from the OS startup or shell being used.  E.G Home / Path Shell: A placeholder for data that can change - value is assigned in a shell script. 
     • Direct Assignment: Specify the variable's value in the command. Value outputted via echo command.
       • echo $var Fearghal
     • Prompt Method: User is asked to enter a value for the variable.
     • Positional Parameters: Parameter passed as argument to command.

3. Exit Status Codes

   • - Sent to the shell when a program or command is quite.  
   • Successful Commands: Exit Status Code = 0
   • Failed Commands: Exit Status Code > 0