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Redis – Sed with two variable

I encountered with behavior incomprehensible to me. 

NODES=6
PORT=6379
until [ $NODES -eq 0 ]
do
        ((NEWPORT=PORT++))
        cp cluster-config.conf redis-$NEWPORT.conf
        sed -i -e "s/$PORT/$NEWPORT/g" redis-$NEWPORT.conf
        ((NODES--))
done

This doesn’t work
But this works

NODES=6
PORT=6379
until [ $NODES -eq 0 ]
do
        ((NEWPORT=PORT++))
        cp cluster-config.conf redis-$NEWPORT.conf
        sed -i -e "s/6379/$NEWPORT/g" redis-$NEWPORT.conf
        ((NODES--))
done

What’s the difference between

sed -i -e "s/$PORT/$NEWPORT/g" redis-$NEWPORT.conf

vs

sed -i -e "s/6379/$NEWPORT/g" redis-$NEWPORT.conf
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2

Answers


  1. 0

    You do a PORT++, which makes PORT to be increased by one.

    By the time you use sed, it’s expanded for 6380, and then it’s not found in the file.

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  2. 0

    You want to create 6 copies of a configuration file, with the existing port 6379 replaced with one of 6380-6385. That’s much more simply written as

    port=6379
nodes=6
for ((newport=port+1; newport <= port + nodes; newport++)); do
  sed -e "s/$port/$newport/g" cluster-config.conf > redis-$newport.conf
done
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