Some BASH script questions

[Craigy90]

Hello,

Recently, I have been trying to write scripts to take care of tasks that I perform frequently. One of these tasks is updating all of the subversion repository checkouts that I watch. Here is an example of what I do:



echo BLENDER
cd ~/Blender/bf-blender/
svn up


which works in most cases.

However, I have run into a problem that I need to work around. In some repositories, I get the following error many times before the update works:



svn: Malformed network data



I looked around a bit, but did not find a solution to this besides updating repeatedly. So, what I thought I could/should do was to continually update until I no longer get the error message by watching for that string. Here is what it looks like now:



var=`svn up`
echo $var

while [ $var=="svn: Malformed network data" ]; do
var=`svn up`
echo $var
done


This seems to have the desired effect, but the command line output is ugly, to say the least:



svn: Malformed network data

svn: Malformed network data

svn: Malformed network data

svn: Malformed network data

svn: Malformed network data

svn: Malformed network data

svn: Malformed network data

U lib/exceptionhandler/exceptionhandler.c U lib/framework/wzglobal.h Updated to revision 5796.
./subversion.sh: line 58: [: too many arguments


What I want it to look like, (it would also be OK if the error lines were included without the newline after each one):



U lib/exceptionhandler/exceptionhandler.c
U lib/framework/wzglobal.h
Updated to revision 5796.


I want to fix this, but I also want to learn more about BASH and the CLI in the process. Also, if anyone knows about that subversion error, that would be helpful too. I would still want to know about handling text output from programs run from scripts like this.

Thanks in advance

[caljohnsmith]

Maybe I'm misunderstanding you, but if the CLI output is "ugly", why do you have the "echo $var" in the loop? Do you want it to output that error every time svn tries, or no? :) What exactly would you like it to do instead?

[Craigy90]

Thanks for the response.

The reason I put echo $var in, is so that it will (hopefully) output the correct subversion. I store the output of `svn up` in a variable so that I can test to see if it is the error that I am trying to avoid.

What I would like it to do, is output each time it tries, and give the error if it occurs. Instead of including the extra line each time with the error message, I want one error per line.

Once it gets through and subversion is correctly updating, I want it to print the output as the program itself normally does. Also, I would like to not have the "too many arguments" error, which is most likely a result of my lack of knowledge of bash. :)

I know you can save error output and normal output to different files, but can you run a program and then determine if an output is one or the other and then take appropriate action?

I am very inexperienced with this sort of thing, but I would like to learn the correct way to approach this kind of problem.

[unutbu]

Try


var=$(svn up)

while [[ "$var" == "svn: Malformed network data" ]] ; do
var=$(svn up)
done
echo "$var"


The reason you are getting this error


./subversion.sh: line 58: [: too many arguments


is because $var in
"[ $var=="svn: Malformed network data" ]"
is getting expanded into many arguments since $var contains a space. So the test has too many arguments and is not really testing what you want properly.

The double-bracket notation is a bashism -- make sure your script begins with
#!/bin/bash, not #!/bin/sh, since by default Ubuntu links /bin/sh to /bin/dash, rather than /bin/bash.

http://tldp.org/LDP/abs/html/testconstructs.html#DBLBRACKETS:


The [[ ]] construct is the more versatile Bash version of [ ]...
No filename expansion or word splitting takes place between [[ and ]], but there is parameter expansion and command substitution.

[Craigy90]

Thank you very much unutbu, that is just what I wanted!

Now let me try to understand how the syntax changed:


var=$(svn up) is a newer way to do `svn up`
I do not want it to print the errors, so don't have an echo before or during the loop
Using double brackets makes the condition be evaluated literally
Putting quotes around $var retains the newlines properly


Thanks again, you were quite helpful. :)