Untitled

$ time while read line; do echo "[ERROR] $line"; done < test.fifo > /dev/null

real    0m0.202s
user    0m0.132s
sys     0m0.056s
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$ time sed 's/.*/[ERROR] &/' < test.fifo > /dev/null

real    0m0.030s
user    0m0.020s
sys     0m0.008s
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$ time awk '{print "[ERROR] " $0}' < test.fifo > /dev/null 

real    0m0.016s
user    0m0.000s
sys     0m0.008s