On Tue, Oct 05, 2004 at 12:41:59PM -0400, Kripa Sundar wrote:
> Dear Gyepi,
>
> > Along a similar vein, I frequently generate sh code from perl rather than
> > simply make 'system()/qx/``' calls from perl. Though there are several benefits to
> > this approach, the most compelling, for me, is the ability to embed 'undo'
> > statements in the generated code so the shell code can, given an 'undo'
> > invocation, rollback the previous run. [...]
>
> What is an 'undo' statement?
> What does "the previous run" mean?
> What does "rollback the previous run" mean?
Here's an example:
My last use of this technique involved a situation where I needed to read a bunch of
text files
containing user information and add the users to /etc/passwd file, add them to various
groups, create their home directories, and add entries to a samba passwd
database, etc, and I wanted all of those operations to have atomicity:
that is succeed completely or fail completely. My perl script read the text
files and a generated a shell script like this:
#!/bin/sh
type=$1
if [ "$type" eq "do" ]; then
groupadd bar
useradd foo ...
gpasswd -a foo bar
...
elif [ "$type" eq "undo" ]; then
userdel foo
groupdel bar
...
fi
except there were more users and more actions.
The script could then be invoked as
./script do
or
./script undo
so if a script invocation with a 'do' argument failed for whatever reason, I could
invoke the script
with an 'undo' argument to restore the system to its previous state.
I hope that makes it clearer.
-Gyepi
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