Awk: transpose – separator in the end – StackOverflow
%%bash time { echo """45 78 45""" | awk 'BEGIN{RS="";OFS=","}{$1=$1}1' }
45,78,45 real 0m0.004s user 0m0.003s sys 0m0.002s
%%bash time { echo """45 78 45""" | paste -s -d, }
45,78,45 real 0m0.004s user 0m0.002s sys 0m0.003s
%%bash time { echo """45 78 45""" | tr '\n' ',' | sed 's/,$//' }
45,78,45 real 0m0.005s user 0m0.003s sys 0m0.006s
import re strings = """45 78 45""" re.sub(r'(?<=\d)\n(?=\d+)', ',', strings)
'45,78,45'