Awk Tips and Tricks

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Finding the length of a line.

A colleague needed to find the length of a particular line in a file. He discovered that using 'wc' gave the wrong result (as in "head -2 filename | tail -1 | wc -c"). Here's what he came up with instead. Note the parentheses...

cat filename | awk '{ if ( NR == 2 ) {print length($0); exit; } } '

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Sizing a directory.

This uses Awk's ability to do arithmetic across multiple input lines to produce a count, total and average file size for a directory or a supplied pattern. It's a usefull tool for quick 'n' dirty system admin...

echo "Harvey's file counter and sizer"
echo "-------------------------------"
if [[ -z $1 ]]
then
   echo "Sizing entire directory"
else
   echo "Sizing files for pattern [$1]"
fi

ls -l >/tmp/fsz.$$_1

# -------------------------------
# Remove any directory entries...
# -------------------------------
grep -v ^total /tmp/fsz.$$_1 | grep -v ^d >/tmp/fsz.$$
rm /tmp/fsz.$$_1
# ------------------------
# Set up the search job...
# ------------------------
if [[ -z $1 ]]
then
   cat /tmp/fsz.$$
     | awk '{s += $5}; END
       {printf "\nThere are %d files matching pattern\nAverage size is %f\nTotal size is %f\n", NR, s/NR, s}'
else
   grep $1 /tmp/fsz.$$ | awk '{s += $5}; END {printf "\nThere are %d files matching pattern\nAverage size is %f\nTotal size is %f\n", NR, s/NR, s}'
fi
rm /tmp/fsz.$$

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Don't use awk - use nawk!

I couldn't work out why this wouldn't work when I ran it using awk (as it worked fine on another machine). It turned out that it would perform admirably if I ran it using nawk instead. It's worth trying this out on your own machine and seeing what happens...

nawk '{ if(substr($0,405,2)=="LS") print $0 }' sourcefile.dat | head -10000 > targetfile.dat

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