Learning to script...

[RJPugh]

Hi folks.

I want to start experimenting with basic shell scripting. I've found several web sites that describe how to do it, and I'll be looking into them in more detail soon. But I want to know which ones you more seasoned BSD users would recommend.

My supply of free time tends to fluctuate, so for now I want to stick with simple stuff. I want to start with scripts that essentially do what the old DOS *.bat files did. That is, execute a set of standard shell commands to complete a common task. I'm not ready for pipes, parameters and other such stuff. I'll get to those later on.

Thanks in advance,

RJPugh

[vermaden]

First things first ... always use #! /bin/sh as script interpreter.

As for the guides, check these for start:

http://developer.apple.com/library/m...roduction.html
http://www.grymoire.com/Unix/Sh.html
http://www.unix.com/tips-tutorials/1...arse-file.html
http://www.ibm.com/developerworks/ai...GoodUnixHabits
http://sparky.rice.edu/~hartigan/sed.html
http://sparky.rice.edu/~hartigan/awk.html
http://www.ibm.com/developerworks/li...wk1/index.html
http://www.shell-fu.org/lister.php?top
http://www.commandlinefu.com/

Shell scripting is generally about efficient parsing/altering the output of commands with sed/awk/cut/find/column/grep/... and using PIPES a lot.

[IdOp]

Probably this is obvious, but it's time to familiarize with the man page for sh. This won't teach programming per se, but give essential information on the capabilities available to you and the syntax required to use them.

Looking at some shell scripts found on your OS itself can be a good idea, trying to figure out what they're doing ... you'll learn some about the OS at the same time. Though, these scripts can get quite complex so don't overdo it or get discouraged.

Doing common tasks is great due to the motivation behind it and seeing results, making mistakes in simple situations and fixing them. You'll soon find you need to add parameters and build up as you go.
Good luck!

[Oko]

The following web-site and pages linked to it contains probably all the information you will ever need about the shell scripting.

http://www.shelldorado.com/links/

Call me and old fashion guy but I would by a book. My favorite is

Classic Shell Scripting by Nelson H.F. Beebe, Arnold Robbins

and if you like me use Korn Shell (pdksh with OpenBSD enhancements also branded by some people removed from OpenBSD project as Mir Korn Shell mksh)

Learning the Korn Shell, First Edition by Bill Rosenblatt (the second edition is worse and done after Bill's death).

I also like Unix Shell Programming, Third Edition by Stephen G. Kochan, Patrick Wood.
You can find on the Internet original Stephen's notes under the name An Introduction to the UNIX shell.

And of course the most important advise as with any programming is that unless you do scripting you are not going to learn it.

[thirdm]

I don't use sh much other than as an interactive shell (actually I kind of dislike shell script, along with Makefile syntax and its various macro/extension packages), but I thought this was a good book:

_The Unix Programming Environment_ Kernighan and Pike.

[Oko]

Originally Posted by thirdm

I don't use sh much other than as an interactive shell (actually I kind of dislike shell script, along with Makefile syntax and its various macro/extension packages), but I thought this was a good book:

_The Unix Programming Environment_ Kernighan and Pike.

It is a VERY good introductory book on Unix as a whole but it is too short too cover any particular topic in great depth. However, highly recommended as the first reading for any novice Unix user.

[raindog308]

I like Chris F.A. Johnson's "Shell Scripting Recipes", though I don't recall at this moment which shell it discusses.

Personally, I would say that shell programming knowledge develops in these stages:

1. A list of commands executed in sequence

2. Same as #1 but verbosely telling the user what's doing and maybe writing to a log file

3. A situation where you might want something to happen, so you learn about if and maybe case

4. You realize you need to consider some input more deeply, so you need to learn basic text processing (cut, sed, maybe simple awk) and variables

5. You decide to make your program somewhat interactive so there's user processing

6. Very soon after, you learn more about error handling because users make mistakes :-)

7. Your programs get bigger and now you're into functions, little libraries, etc. You are using variable scoping, coroutines, arrays, and lots more awk, sed, etc. Maybe you go crazy and start using tput to write interactive curses menus :-)

8. You've outgrown shell and move on to perl, python, ruby, or really move on and start writing C.

I am not entirely serious about #8. I've maintained multi-thousand-line shell scripts and with enough programmer discipline, you can write huge things in shell.

[gso]

8. read books on formal specification languages, take a sabbatical, teach yourself JSP, write COBOL programs for a while, return to posix SH and write highly competent command line utils using structured programming techniques and a strict procedural style

9. get a job as a C programmer