Introduction to Shell Scripting

Prof. Brian D. Davison

Computer Science & Engineering, Lehigh University

Announcements

• Project #4 (debugging) online, due Thursday
• Friday's quiz is on the shell scripting from today, as well as anything from previous classes
• I will link to bash tutorials, references after class
• Today's schedule
  • Return short quiz #5 -- scores ranged from 2 to 10, mean 6.5
  • Course Feedback
  • Introduction to Shell Scripting
    • See UNIX Shells by Example, Ch 1&2, focus on bash

Course Feedback

• Course is essentially half over -- I will be filing mid-term grades soon (tomorrow)
• We have covered
• Using UNIX
• Programming with C
• We still have to cover
  • UNIX Shell programming
  • UNIX Systems Programming
• This is your chance to have an impact on how the rest of the course will be structured
  • We will still have a second exam, and a final
  • We will stlll have some labs and lectures
• What should be different about the rest of the class? What should stay the same? What will help you learn the best?

Automating UNIX Operations

• You know many UNIX commands
• We will cover more...
• You know how to program in C and other languages
• You have also seen how to connect UNIX commands with pipes
• UNIX commands can also be placed into shell scripts
  • What is a shell?
  • What is a script?
• Try writing one

What does the shell do?

• After you type a command, the shell
• Performs history substitution (if necessary)
• Breaks up the command line into tokens
• Updates the shell history
• Processes quotes
• Performs alias substitution
• Sets up redirection, background processing, and pipes
• Performs variable substitution (e.g., $user)
• Performs command substitution (ls `cat filelist.txt`)
• Performs filename substitution (handling wildcards, etc.)
• Executes the program