CODEWITHSUNDEEP
bashwhile-loop
Heliosh
Heliosh

Reputation: 97

while read incredibly slow

As far as I understand, "while read" is so slow, because it reads byte-wise. Is there a more efficient way to do this if line-wise is sufficient for me?

I have a file data.txt containing four parameters per line:

1 56 56 48
3 646 86 656
4 56 894 959
6 89 849 875

etc.

and i want to perform an operation on each line (assign each value to a variable for further processing).

this is how i do it now:

cat data.txt | 
while read linewise; do
par0=`echo $linewise |awk '{print $1}'`; 
par1=`echo $linewise |awk '{print $2}'`;
par2=`echo $linewise |awk '{print $3}'`;
par3=`echo $linewise |awk '{print $4}'`;

echo $par0 $par1 $par2 $par3
done

But for a ~1000 line file this takes half a minute:

real    0m30.380s
user    0m7.996s
sys     0m11.820s

How can I speed this up?

Upvotes: 2

Views: 1312

Answers (1)

arco444
arco444

Reputation: 22821

You could speed it up by removing all the pipes and calls to subshells. The below greatly simplifies what you're doing: 

while read -r par0 par1 par2 par3; do 
  echo $par0 $par1 $par2 $par3
done < data.txt

Upvotes: 5

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