Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
• Some things you should know.
• Files and directories.
• Command-line patterns.
• File and directory permissions.
• I/O redirection.
• Variables.
• Command-line history.
• The script command.

Preliminaries

Admin

• There has been a request that we cover cron issues. Would people like to do that?
• Homework:
  • Part 0: Create a directory for yourself in the repo.
  • Part 1: Write a program that cleans up after script. Put it in the repo. (I'd recommend using C, but it's up to you.)
    • I'm sure you can find one. You learn more by writing it.
  • Part 2: Write a bash script that finds all of the files under the current directory that end with .jpg and moves them to a directory called images. Put it in the repo.
  • Part 3: Suppose I have a file called * in my directory. How do I remove. Suppose I have a file called -rf *, how do I delete it?

Questions

• I need some help understanding that Make stuff. Will you help?
  • Answer: Eventually.
  • Good Unix programmers find that Make is helpful to automate tasks
  • Example: Class outlines in Sam's world
    • Administrative stuff
    • Links
      • Based on the day of the semester (vary)
      • Based on the subject matter (consistent)
    • Short summary
    • Overview
    • Detailed information

Some things you should know

• Files and directories.
• Command-line patterns.
• File and directory permissions.
• I/O redirection.
• Variables.
• Command-line history.
• The script command.

Files and directories

• Two ways to think about it: Internal (behind the scenes) and external (client model)
• File is a collection of data. Bits! With a name.
• Many mechanisms for telling the type of the file.
  • Custom: Extension gives you information. .txt is a text file (usually *nix or Mac), *.jpg is an image file using the JPEG image format, .c is a text file containing C code.
  • Custom: A header (first few bytes) that describes the content First two bytes correspond to the ascii values #!, Unix thinks it's a script.
  • Experiment: Can I open it with ...?
  • Compute: Inspect the data
• Note: The file command tells you an approximate type, based on suffix and content and first few bytes.
• Directory is a collection of files and other directories.
• Unix tries to distinguish the two.
• Internally, every file has one or more inodes, which has an address, access information, some file type data, some data, and (optionally), a link to the next inode.
• The directory maps names to inodes.
• Unix treats lots of things as files, including devices.
• Know commands for making files and list files and making directories and list directories.
  • mkdir - create a directory
  • ls - list files
    • If the parameter is a directory, lists all of the elements in that directory
    • Given multiple parameters, processes each in turn
    • Flags: -l is detail, -t organized by time, -F suffixes, -R recursive, -a hidden

Command-line patterns

• ls * - everything
• ls *.x - everything that ends in .x
• ls {foo,bar}.c
• More: See notes and documentation

File and directory permissions

• Three basic kinds: user, group, other
• For each category, three characteristics: read (4), write (2), execute (1)
• Slightly different meanings for directories

I/O redirection

• >, <, |
• stdout vs. stderr
  • stdout is where the normal outpt of your program goes
  • stderr is supposed to be where error messages go

Variables

Command-line history

The script command