[NTLUG:Discuss] Linux script question

[Bug Hunter]

On Mon, 16 Jun 2003, Rusty Haddock wrote:

> Bug Hunter wrote:
snip>     >> > 
>     >
>     >  for a single file:
>     >
>     >  sed /oldtext/newtext/ filename > filename.newfile
>     >  rm -f filename
>     >  mv filename.newfile filename
>     >
>     >  
>     >in bash
>     >
>     >  for i in /dirname/*
>     >do
>     > sed /oldtext/newtext/ $i > $i.newfile
>     > rm -f $i.newfile
>     > mv $i.newfile $i
>     >done
> 
> Be careful here!!!  I see two problems here:
> 	1) Why are you nuking the .newfile you just created???
> 	   Just delete the 'rm' command.

 yep.


> 
> 	2) If the 'sed' script fails you're still gonna nuke your
> 	   old files!!!  How would 'sed' fail?  Oh, a full file
> 	   system for one way.  There are others.  "Been there,
> 	   lost that!"  One of the better things to do is to join
> 	   the 'mv' to the 'sed' with a '&&'.  This way, if the
> 	   'sed' fails you don't do the 'mv'.  For example:
> 	   	
>     	sed /oldtext/newtext/ $i > $i.newfile && mv $i.newfile $i
> 
 good idea


> 	    Remember that the SHELL is the one who will create the
> 	    .newfile, not the 'sed' command.  It is created before
> 	    the 'sed' program is even run -- it has to be otherwise
> 	    'sed's stdout won't be connected to anything.
> 
>     >  This was given to me by a fellow named Richard a while back. :)
> 
> Be caseful what Richard tells you for now on. :-)  Yes, it'll work
> (well, remove the 'rm' like) 99.9% of the time.  Alas, 0.1% of the
> time it will lose what you spent 99.9% of the time creating! :-(
> 

  Well, a loaded gun in the wrong hands.....


  I always make a copy of the directory and run it on the copy until I'm 
happy.  Then I move the original to a backup directory, and move the copy 
to the original, if possible.  (sometimes a reboot or restart of the 
demon is required.)

  Discretion is the better part of system administration.  Or is that 
valor?

   I had *assumed* intelligence on the other side.  Also had assumed that 
if they had not been there, done that, they would soon learn and never do 
it twice.  Or in my case, the third time is the charm. <grin>

bug