convoluted code Post: 302666549

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The Lounge War Stories convoluted code Post 302666549 by alister on Wednesday 4th of July 2012 05:23:49 PM

07-04-2012

Registered User

Quote:

Originally Posted by methyl

Footnote: For anybody following this thread, this is a discussion thread.
@jgt is expert and definitely did not ask this question.

I must confess that I was confused until that footnote clued me in to the fact that I wasn't in the shell scripting forum anymore (got here via the 'new posts' link). Smilie

Quote:

Originally Posted by methyl

Until looking at unix.com I had never seen the for var in <open-ended list> construct ever ... and still wonder which course/manual/book/rumour it comes from?

I don't know for certain, but my first impulse is to blame GNU Bash. I've seen that idiom recommended as the correct way to work around the fact that the final command in a bash pipeline runs in a subshell.

From the Advanced Bash-Scripting Guide's Bash Gotchas:

Code:

# Loop piping troubles.
#  This example by Anthony Richardson,
#+ with addendum by Wilbert Berendsen.


foundone=false
find $HOME -type f -atime +30 -size 100k |
while true
do
   read f
   echo "$f is over 100KB and has not been accessed in over 30 days"
   echo "Consider moving the file to archives."
   foundone=true
   # ------------------------------------
     echo "Subshell level = $BASH_SUBSHELL"
   # Subshell level = 1
   # Yes, we're inside a subshell.
   # ------------------------------------
done
   
#  foundone will always be false here since it is
#+ set to true inside a subshell
if [ $foundone = false ]
then
   echo "No files need archiving."
fi

# =====================Now, here is the correct way:=================

foundone=false
for f in $(find $HOME -type f -atime +30 -size 100k)  # No pipe here.
do
   echo "$f is over 100KB and has not been accessed in over 30 days"
   echo "Consider moving the file to archives."
   foundone=true
done
   
if [ $foundone = false ]
then
   echo "No files need archiving."
fi

Regards,
Alister

alister

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NAME

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SYNOPSIS

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OPTIONS

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EXIT STATUS

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