Adding Some Spice To *nix Shell Scripts

An anonymous reader writes "Developing GUI script-based applications is time-consuming and expensive. Most Unix-based scripts run in a CLI mode or over a secure ssh session. The Unix shells are quite sophisticated programming languages in their own right: they are easy to design and quick to build, but they are not user-friendly in the same way the Unix commands aren't (see the Unix haters books). Both Unix and bash provide features for writing user friendly scripts using various tools to build powerful, interactive, user-friendly scripts that run under the bash shell on Linux or Unix. What tools do you use that spice up your scripts on the Linux or Unix platforms?"

Comments

Pashua on OS X

[iliketrash]

On OS X, I use Pashua, http://www.bluem.net/en/mac/pashua/. This is a brilliantly simple thing to use. I also use it for other (non-script) languages for making a quick-and-dirty GUI that still looks nice and is a real Cocoa program.

Off the top of my head...

[hkz]

I work as a Linux netadmin and system developer, so I do a lot of shell programming in (ba)sh. Here's some of the niftier things you can do to a shell script:

- Make colored output with shell escape sequences. Works especially well with red type for error messages, makes them really stand out.
- Use inline functions a lot. The great thing about them is that you can pipe to them and use them in all kinds of places. For instance, to do mysql queries:

mysql_query() { /usr/bin/mysql --user=root --pass=topsecret database
}

echo 'SELECT * FROM accounts' | mysql_query

- "Here documents". For long MySQL sequences, something like the following (reusing the mysql_query function from above):

cat - EOF | mysql_query
      SELECT bar
      FROM foo
      WHERE baz ...
EOF

This lets you easily format stdin for scripts and other programs. Also really useful for outputting HTML and stuff like that. Best thing is that variables are expanded inside the block.

- The || and && operators. Check if a file exists, remove if so, else complain:
[ -f /tmp/somefile.txt ] && rm /tmp/somefile.txt || echo "Does not exist!"

Also common in this form:
[ -x /usr/bin/necessaryprogram ] || { echo "aaargh"; exit 1; }

- Making a "multithreaded" shellscript is also one of my favourites. Say, you want to start five virtual machines at the same time. Write a function that starts a vm, and call it a few times in a loop, backgrounding each instance with &, and saving their PIDs. Then have a "wait loop" that waits for the PIDs to exit the system (or for a timeout to occur).

- Proper argument handling with getopt. Have your script take "real" arguments in any order, just like real binaries.

This just scrapes the surface of the surface, of course. I learn new stuff every day.

Re:None, I have given up bash scripting

[Hatta]

Does `find . -print0 | xargs -0` really qualify as "serious hack magic"?

tools I found useful

[tpwch]

Here are some random things I find useful, related to user interaction (mostly becuase it notifies the user):

Oven timer:
sleep $((20*60)); xmessage "Dinner is done"

Quick macro for automating some repetitive task in a program:
xdotool type "something"; xdotool key Return; xdotool mousemove $x $y; xdotool click 1; (and so on)

Copying a file to/from the clipboard (can also copy from /topipe, so the output of any command). Faster than opening a text editor:
xclip -in file

Notifying me when some specific thing changed on a website:
CHECKLINE="$(curl -s http://somewebsite.org/somepage.html | grep "currently undergoing maintenence")"
while true; do
    sleep 120
    [ -z "$CHECKLINE" ] && xmessage "somewebsite is open again" && exit
done

Or just checking for changes in general (I use this for notifying me when something changed when tracking something I ordered, so I know the minute the package is ready to get picked up at the post office):
while true; do
    OLD_MD5=${MD5}
    CONTENT=$(elinks -dump 1 -dump-charset iso-8859-1 "http://someurl.com/track?id=someid")
    MD5=$(echo -n $CONTENT | md5sum -)

    [ "${MD5}" != "${OLD_MD5}" ] && {
        xmessage "$(printf "New action: :\n\n${CONTENT}")"
    }
    sleep 120
done

If you don't want to interrupt what you're doing with a pop-up you can pipe it to osd_cat instead to have the text appear over whatever program you're currently working with. Adding a few beep; beep; beep; beep; is also a good way to get your attention if you're not paying 100% attention to your computer all the time.

Best book for this -- hands down.

[CFD339]

Linux Shell Scripting with Bash
by Ken O. Burtch
Sams Publishing

One of only two "computer" books I've ever been able to just sit down and read rather than just using as reference (the other being Kathy Sierra's "Head First Java" -- which is amazing).

Ken does a fantastic job at putting "just the right" level of background, detail, context, and and depth for someone new to shell scripting to get started, then to use the book as a reference for all the traditional tools (sed, awk, etc..).

I've bought two copies, one for me and one I gave to someone else who wanted to learn how to do this stuff.

Re:Best book for this -- hands down.

[actionbastard]

The only bash scripting guide you will ever need:

http://tldp.org/guides.html

free as in beer.

Re:None, I have given up bash scripting

[DaleGlass]

Use:

tar tf file.tar | xargs -d "\n" rm

That will work unless the filenames contain newlines in them.

Re:Nice example.

[hkz]

Thanks, it's nothing I couldn't show a fella. Learnt a lot from my colleagues and from the O'Reilly 'Unix Power Tools' book. The Advanced Bash Shell-scripting Guide is pretty good (but chaotic) too.

The syntax filter here munged some of the examples, though. The here document example will not work as-is, because there should be two 'less-than' signs in front of the minus sign. The mysql_query function probably also won't work (can't bother to run a test), because the newline after the first bracket mysteriously disappeared. So best to loop up the concepts in some kind of reference manual.

"Interaction"

[betterunixthanunix]

The way I look at it is this: the "interaction" may actually be with another script. The whole abstraction that Unix-like OSes enforce, at least with file based IO, is that it is irrelevant what is on the other side of a file descriptor -- a disk, a pipe, a user, a socket, or something else entirely.

Of course, this all starts to break down with GUIs.