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Logical and vs. conditional loop

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# 1  
Old 05-22-2009
Logical and vs. conditional loop
Simple question. What's the difference (pros and cons) between these two:

Code:
if [ -n $_var] ; then
    condition1
elif [ -z $_var ] ; then
    condition2
fi

Code:
[ -n $_var ] \
    && condition1 \
    || condition2

Is the second method faster as the whole line gets loaded into memory? Just looking for some tips of when I should use one or another.

Thanks!!

Vic
# 2  
Old 05-22-2009
First, those are branching expressions, not loops. Now that we have the terminology out of the way: The first one has better readability and is easier to maintain should there be the need for additional commands in one of the blocks. The second one is simpler, but should condition1 fail, condition2 will still be evaluated. I don't think there's any difference in speed or memory consumption (at least I never experienced any) since shell scripts (at least ksh/bash/zsh) are compiled at execution time and not read line by line (like .bat/.cmd files in Windows).
Just my €0.02
# 3  
Old 05-23-2009
Conditional execution (not loops)
Quote:
Originally Posted by victorbrca
Simple question. What's the difference (pros and cons) between these two:

Code:
if [ -n $_var] ; then
    condition1
elif [ -z $_var ] ; then
    condition2
fi

Code:
[ -n $_var ] \
    && condition1 \
    || condition2

Is the second method faster as the whole line gets loaded into memory? Just looking for some tips of when I should use one or another.

The two are not equivalent.

In the form:
Code:
command1 &&
 command2 ||
  command3

command3 will be executed if either command1 or command2 fails.
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