How Would You Like Your Loops Served Today? Post: 302655867

Sponsored Content

The Lounge What is on Your Mind? How Would You Like Your Loops Served Today? Post 302655867 by Scrutinizer on Thursday 14th of June 2012 01:44:37 AM

06-14-2012

Moderator

I have preference for whatever is simplest and the most intuitive to read..
I agree that specifying data at the end of the loop is a bit of an oddball, but:

To me it is the simplest and cleanest code, there is no need for a cat-and-pipe or an extra file descriptor
As noted above, in shells other than ksh it does not send the loop into a subshell, so not only is that more efficient, it ensures variables set inside the loop are available outside. I tend to go with what works in all shells. The way it is done in ksh is great, but it is not specified in POSIX.
Whenever I have a loop with more than 20 lines of code, I tend to start thinking about splitting it into functions with mnemonic names.
With regards to the use of redirects, I have a preference for using them only in the context in which they are used. Also, feeding them into the loop at the bottom is ideal, since the file descriptors get closed when the loop ends. With the exec examples you would need to use an explicit close afterwards.

Last edited by Scrutinizer; 06-14-2012 at 03:35 AM..

Scrutinizer

View Public Profile for Scrutinizer

Find all posts by Scrutinizer

4 More Discussions You Might Find Interesting

1. IP Networking

to serve or be served??

I have two machines on my network - one OSX mac and one linux box. The mac is my main workhorse, and the linux box does occasional chores and webserving. Currently the mac shares (via NFS) files with the Liinux box. Would it be less demanding on the mac if I made it a client, and moved my files...

2. Web Development

Symbol Links amongst Apache's served files, is this a security-don't?

I read somewhere that you should make sure Apache is configured to not allow symbolic links to be followed outside the webroot, as this can compromise security. I can imagine how this could lead to a security risk: eg: Is my assumption correct? -- Is it nothing more than: "its just...

3. Shell Programming and Scripting

meaning of today=${1:-${today}}

what does today=${1:-${today}} mean??? I saw a script which has these two lines: today=`date '+%y%m%d'` today=${1:-${today}} but both gives the same value for $today user:/export/home/user>today=`date '+%y%m%d'` user:/export/home/user>echo $today 120326...

4. AIX

VIOS backupios -mksysb - does it need to be served by a NIM server ?

working through VIOS backup options. Generally, we store mksysb's on a server and then NFS mount them from it to copy to a VIO optical library, etc. In the case of a VIO backup, I see the -mksysb option to backupios and understand that it doesn't include the NIM resources in the backup. ...

LEARN ABOUT OSF1

break

break(1)                                                           User Commands                                                          break(1)

NAME

       break, continue - shell built-in functions to escape from or advance within a controlling while, for, foreach, or until  loop

SYNOPSIS

   sh
       break [n]

       continue [n]

   csh
       break

       continue

   ksh
       *break [n]

       *continue [n]

DESCRIPTION

   sh
       The break utility exits from the enclosing for or while loop, if any. If n is specified, break n levels.

       The continue utility resumes the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

   csh
       The  break  utility  resumes  execution after the end of the nearest enclosing foreach or while loop. The remaining commands on the current
       line are executed. This allows multilevel breaks to be written as a list of break commands, all on one line.

       The continue utility continues execution of the next iteration of the nearest enclosing while or foreach loop.

   ksh
       The break utility exits from the enclosed for, while, until, or select loop, if any. If n is specified,  then  break  n  levels.  If  n  is
       greater than the number of enclosing loops, the outermost enclosing loop shall be exited.

       The  continue utility resumes the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-
       th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words that follow a command preceded by ** that are in the format of a variable assignment are expanded with the same rules as a  vari-
           able  assignment.  This means that tilde substitution is performed after the = sign, and also that word splitting and file name genera-
           tion are not performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), exit(1), ksh(1), sh( 1), attributes(5)

SunOS 5.10                                                          17 Jul 2002                                                           break(1)