topic Re: xdev in Operating System - HP-UX

xdev

Waugh — Thu, 06 Nov 2008 14:08:50 GMT

Hi,

How xdev and xargs helpful in scripting. how its working. What is the use of it. Pls explain

Reagrds
Rkumar

Re: xdev

James R. Ferguson — Thu, 06 Nov 2008 14:19:53 GMT

Hi:

I assume that by 'xdev' you mean the '-xdev' option of 'find'. This option prevents 'find' from crossing mountpoints. This is extremely useful when you truly want to only search the root filesystem, as in:

# find / -xdev -type f -mtime -30

...which would find files modifed during the last 30-days.

In the case of 'xargs' is seen in pipelines to construct lists of things on which execution is performed. Since 'xargs' can collect multiple arguments into a list of arguments it can be used to greatly reduce the number of processes that you need to spawn. A classic example of this is again with 'find'. Consider:

# find / -xdev -type f -mtime -30 -exec ls -l {} \;

...This spawns an 'ls' command for *every* file found (and therefore becomes costly).

# find / -xdev -type f -mtime -30 | xargs ls -l {}

...spawns only one or very few processes depending on the argument list size making this very efficient.

Now, in truth, 'find' has a newer syntax with its '-exec' that accomplishes the same thing as an 'xargs' pipe:

# find / -xdev -type f -mtime -30 -exec ls -l {} +

The "+' instead of the escaped ";" triggers 'find's inbuilt buffering.

Regards!

...JRF...

Re: xdev

Ganesan R — Thu, 06 Nov 2008 14:43:48 GMT

Hi,

xdev:
xdev is to restrict search not to cross mount points. Default search will do it on mount points as well.

For example if you want to search only on / and not to seach /var, /etc, etc then you need to specify xdev

#find / -xdev -name *.txt -print

xargs:
when you use -exec to pipe the output of find command to perform something else,
-exec will start a new process for each line of the output. Sometime -exec may not be able to handle this and command seems to be hung. xargs handle this perfectly. It will start only limited process

#find / -user abc |xargs rm -rf {}