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Full Discussion: grabbing more than one argument in a loop
Top Forums Shell Programming and Scripting grabbing more than one argument in a loop Post 302289520 by bakunin on Thursday 19th of February 2009 09:41:07 PM
Old 02-19-2009
Quote:
Originally Posted by Intense4200
But how do I go about reading more than one item at a time in a for loop?
First off, you shouldn't use for-loops for that purpose at all. A for-loop loops through a list of values and as soon as this list gets longer than the maximum line length the shell can handle (as per POSIX 4096 characters are guaranteed) the command will break.

The shell evaluates first what you have written in backticks and replaces the command with its output, basically putting the whole content of the file on the command line. Only then the for-loop is executed.

Use a while-loop for that purpose so you do not run the risk of the commandline getting too long with the added benefit of being able to cycle any number of variables instead of only one:

Code:
cat /path/to/file | while read valueA valueB ; do
     echo Value1 = ${valueA} \tValue2 = ${valueB}
done

Some might say that it would be possible to save the one pipeline by writing the feeding file at the end of the loop:

Code:
while read valueA valueB ; do
     echo Value1 = ${valueA} \tValue2 = ${valueB}
done < /path/to/file

While this is syntactically correct IMHO the first version is easier to read and to maintain, which is why i prefer to do it this way.

I hope this helps.

bakunin
 

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LEARN ABOUT PHP

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)
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