merge_line

#!/bin/bash
# read from pipeline, and merge per n lines to one line, and output to stdout
# usage: merge_line          # merge per 2 lines to one line, and separate with " "
#        merge_line "="      # merge per 2 lines to one line, and separate with "="
#        merge_line 3        # merge per 3 lines to one line, and separate with " "
#        merge_line 4 "##"   # merge per 4 lines to one line, and separate with "##"
# created by zhouwei on 2019-08-28

# default value
n=2
separator=" "

count=$#
if [[ $count -eq 0 ]]; then
    n=2
    separator=" "
elif [[ $count -eq 1 ]]; then
    if [[ "$1" =~ ^[0-9]+$ ]]; then
        n="$1"
    else
        separator="$1"
    fi
else
    n="$1"
    separator="$2"
fi

i=0
awk '{print $0}' | while read line
do
    if [[ $i -gt 0 ]]; then   
        if (( i%n == 0 )); then
            echo ""
        else
            echo -n "$separator"
        fi
    fi
    echo -n "$line"
    ((i++))
done

echo ""

exit 0