I tried to read some lines from a file and append them to a variable via "while" block like below:
###############
#!/bin/sh

test="ABC_"

while read L1
do
test=$test$L1
echo $test
done < some.txt

echo $test
###############

But the last line keeps print the initial value, "ABC_", even i can see that the $test is changed in the while block. And if i remove "< some.txt" and put the "read" command inside the block, the updated $test will be printed on the last line.

Could you please explain why such thing happens and how can i fix it if i still want to keep "< some.txt" at where it is...

Thanks in advance