/tmp <king@king> test.sh 2>/dev/null
abcd
efgh
ijkl
------------------------
abcd
------------------------
abcd
efgh
ijkl

#!/bin/bash
some_command()
{
	while read line
	do
		true
	done
	echo "${@}"
}

# 默认全部输出
cat data.txt |
while read line
do
	echo "${line}"
done

echo "------------------------"

# read line的输入被some_command全部吃掉了，导致就一行
cat data.txt |
while read line
do
	some_command "${line}"
done

echo "------------------------"

# 在调用吃stdin的子shell前，先关闭stdin
cat data.txt |
while read line
do
	some_command "${line}" <&-
done

/tmp <king@king> 12:27:15 $ cat data.txt 
abcd
efgh
ijkl