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GNU cfengine

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3.14 Iterating over lists

Shell list variables are normally defined by joining together a list of directories using a concatenation character such as `:'. A typical example of this is the PATH variable:

 
PATH=/usr/bin:/usr/local/bin:/usr/sbin

It is convenient to be able to use such variables to force cfagent to iterative over a list. This gives us a compact way of writing repeated operations and it allows a simple method of communication with the shell environment. For security reasons, iteration is supported only in the following contexts:

This typically allows communication with PATH-like environment variables in the shell.

In these contexts, any variable which has the form of a list joined together by colons will be iterated over at compilation time. Note that you can change the value of the list separator using the split variable in the control section of the program (see Reference manual).

For example, to link all of the binary files in the PATH environment variable to a single directory, tidying dead links in the process, you would write

 
control:

  actionsequence = ( links tidy )

links:

  /allbin +> $(PATH)

tidy:

  # Hopefully no-match matches nothing

  /allbin pattern=no-match age=0 links=tidy

no-match is not a reserved word in cfengine, this is just a string you do not expect to match any file.

Alternatively, you might want to define an internal list using a space as a separator:

 
control:

   split = ( " " )

   mylist = ( "mark ricky bad-dude" )

tidy:

   /mnt/home1/$(mylist) pattern=*.cfsaved age=1

This example iterates the tidy action over the directories `/mnt/home1/mark', `/mnt/home1/ricky' and `/mnt/home1/bad-dude'.

The number of list variables in any path or filename should normally be restricted to one or two, since the haphazard combination of two lists will seldom lead to any meaningful pattern. The only obvious exception is perhaps to iterate over a common set of child-directories like `bin', `lib' etc in several different package directories.


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