Day 3

1. Day 3 Review The Shell Additional Commands

2. Things to Review • Lets spend some time going over questions from the last class. • Ask about any Unix command you don’t understand • Concepts you have never seen before. • We will try to get everyone to a level playing field.

3. What is a shell? • Basically a command interpreter • Runs programs • Returns output • Allows you to write shell scripts to automate things • Many different shells • bash • c-shell • zsh

4. Tab Complete • Makes life much easier. • Less error prone • Faster • Will complete file names, or commands. • Its smart enough to know what its trying to complete. • Also handy if you just don’t remember what you are looking for when you are running a command.

5. Previous commands • Up/Down arrows recall previous commands • You can also use: • !ls • To recall the last time you used a command starting with ls • !tar • For example will recall the last rpm command which might have been • tar cvf all.tar a.txt b.txt c*

6. Editing previous command lines • You can also set your shell to use your favorite VI commands. • set -o vi • Will make the shell use the VI editor for command line editing. • This allows you to recall last commands with • [Esc] k • or to edit a command line to delete a word or to do other vi things.

7. Shell Startup • Each shell is started by executing the program /etc/profile • Users can modify their environment by changing .bash_profile • For example if you liked what we just did to make vi your editor on the command line, you could put that into your .bash_profile.

8. aliases • An alias can be used to make more friendly commands for things which you always forget: • In dos you use dir, in Unix you use ls. • What if you want to be able to type dir in Unix, and have it work the same: • alias dir=ls • sometimes its hard to remember how to use tar: • alias untar=“tar xvf” • Now you can: • untar file.tar

9. Environment Variables • Type the command: • set • To see a list of all variables set in your shell • This includes your PATH and others. • You can modify these directly or change them in your .bash_profile, so they will always be what you set them to.

10. export • Children don’t see environment variables unless they are exported. • Each shell has its own environment.

11. Sed • Sed is a very handy command for editing a text file. • VI can edit a text file, but you can’t use vi in a script. It requires human interaction • sed allows you to do what vi can do, directly from the command line: • sed ‘s/a/b/’ myfile • Would open myfile, look for all occurrences of the letter a, replace it with the letter b, and output the new file to the screen.

12. 3 Input/Output channels. • Standard In (0) • Typically this is your keyboard • Standard Out (1) • Typically this is your screen • Standard Error (2) • Typically this is your screen also.

13. Each can be redirected. • command < input.file • command > output.file • command 2> error.file • command > all.output 2>&1 • command >> appended.file

14. Pipes • Any commands output can be piped into another process. • There is no limit to the number of pipes you can output • ps –auwx | awk ‘{print $1}’ | sort | uniq > output

15. Find • Lost a file? • find / -name ‘enda.txt’ –print • Most systems understand the –print by default.

16. Using VI • Good idea to know. • Not all systems have Joe/Emacs/etc installed. • They all have vi. • Slow to learn, but very powerful later. • Learn the basics we’ll get to the advanced stuff later.