Real life SHELL SCRIPTS usage?

I'm learning UNIX/LINUX shell scripting and trying to think about it appropriate usage?

The only thing that comes into mind - it'll be nice for let's say backup operations and logs management....But I'm sure it goes way beyond that...or开发者_JAVA百科 is it? I'm sure there are people on this server who use Shell scripting on the daily basis. Can you tell me what do you use it for in your organization/business?

Thanks:)

Why use shell scripts

Basically, there are any number of tasks related to backup, maintenance, etc. that need to be automated, and shell scripts do that.

You can do quite everything in shell, but it is easy to write ugly and slow scripts.

First domain of expertise of shells is to start and combine other programs. This is exceptionally well suited for:

• file manipulations: list, move, copy, compress, archive
• text lines manipulation: filter (grep), modify (sed), delete lines (sed), combine files (paste), sort (sort), unify (sort -u)

All those operation are NOT shell operation, but the shell is the glue that put them all together.

• file operations are generally combined with flow control instructions (while, if, for)
• line operations are combined with pipes | and named pipe mkfifo

Things you can do in less than 20 lines with shell commands.

I personally use it to batch miscellaneous daily/weekly commands and start up long running processes. They can be unwieldy and hard to debug when they get big. Unknown variables evaluate to empty strings (icky).

Scripting languages languages such as Python, Perl, and Ruby become more attractive as the code becomes more complex.

I work on an actively developed software project that runs in a unix environment. Unfortunately it uses a lot of different environment variables for configuration and stashes binary programs, data files, and shared libraries on version dependent paths.

All that is a pain to set up.

But it gets worse: at any given time I might want to work with the stable version, the pretty-stable-but-more-up-to-date version, the bleeding-edge-every-new-feature version, or my personally hacked development version.

Switching between them is a even bigger hassle.

Enter a shell script which insures that I am set up for exactly one version at a time. Ta da!

BTW--The script I use for this makes extensive use of the accepted answer to How do I manipulate $PATH elements in shell scripts?, so you know Stack Overflow works for me in the real world. More over, I've infected several other people with this technology.

I've seen and worked-on full-blown applications (medical records and scheduling processing) written in Korn shell.

Batch programming, PostScript print filters, automatic mailers and automated airline checkin systems, regular stock price tracking, software installers, et al, et al.

Better question = what could not be programmed in Shell?

for our company, we use shell scripts for the following:

backups - it would be very disastrous for us if we lose our data. Various parts of our backup like database backup, offsite backup, continuous backups etc all uses shell scripts that runs daily and some runs once a week. update dates - we do not use ntp so we rely on sh scripts to update the date due to firewall restrictions. log cleanup send emails

I didn't think bash programming was particularly powerful until I saw that the OS startup scripts are all written in it. That made me re-examine my assumptions. I now have several dozen important shell scripts that I've written over the years that automate some common tasks.

For example, I wrote one that polls the current load average, and then executes a provided command if it exceeds a certain value (useful for examining events that only happen once or twice a day).

Another that I wrote iterates through all the mysql databases on the server and outputs a mysqldump for each one into its own appropriately-named .sql file.

Another iterates through a list of homedirs and changes the ownership of all the files under the corresponding public_html dir to match the user who should own them to be compliant with suPHP's restrictions.

Another examines the current hardware configuration and downloads, installs, and configures appropriate software for monitoring the health of the currently-attached RAID controller.

These are all relatively simple tasks that could be done by hand -- but whenever I find myself doing the same task more than once, I write a shell script to automate the process.

I also built a base-64 decoder in bash just to see if I could. It works, but it's terribly slow. I use shell scripting for simple tasks that primarily involve executing other programs. I often use Perl when a significant amount of string processing is required, and I use Python for the more complex scripting tasks. The more languages you know, the better you will be at choosing the right one for the job.