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Re: Another mapfile question.

From: Steven W. Orr
Subject: Re: Another mapfile question.
Date: Fri, 05 Aug 2011 10:32:54 -0400
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv: Gecko/20110616 Thunderbird/3.1.11

On 8/5/2011 9:08 AM, Maarten Billemont wrote:
while read line
done<  fn

You should really put that IFS= on your 'read', so as not to break the default 
wordsplitting for the rest of your script:

For purposes of giving concise examples on this email list, I wrote it as above. In practice, something like the above construct that modifies IFS would be responsible for restoring IFS. e.g.,

# do stuff

More often, the code would be placed in a subroutine where IFS is declared as a local variable. Within that routine, if IFS needs to be restored, then old_IFS would also be locally declared. If IFS did not need to be restored (within the routine) then old_IFS might not even need to be declared.

One trick that bit me a while back, is that the order of declaring IFS and old_IFS is important. It has to be done in this order:

    typeset -r old_IFS="$IFS" # Must come first
    typeset IFS


This is because the initial value to old_IFS is referring to the outer scoped IFS. It is nice though that the locally declared IFS gets an initial value from the outer scope :-)

while IFS= read -r line

aa=($(<  fn))

Don't leave expansions unquoted!  you're still permitting pathname expansion 

IFS=$'\n' read -rd '' -a aa<  <(fn)

mapfile -t aa<  fn

When compared to the above read, this will also read empty lines.  The read 
operation will merge multiple newlines into a single delimiter (as it does for 
all types of whitespace in IFS).

The while read works fine but is verbose.  The mapfile is a bit more concise.  
The read -a is fine and concise so long as you can live with the lack of empty 
lines.  I doubt mapfile is much use to you that while read doesn't already give 

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happened but none stranger than this. Does your driver's license say Organ ..0
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