Consider I have a file with contents available in it
cat file | read; echo $REPLY
gives empty output
read < file; echo $REPLY
gives first line of the file as result
while IFS= read; do :; done < file; echo $REPLY
prints nothing, empty output. I expected here the last line of the file as the ouput since I thought the iteration would occur till the end of the file is reached and the last line would be retained in REPLY variable. Any reason for this behavior?
while IFS= read; do :; done < file; echo $REPLY
The above reads each line of the file, one by one. After it reads the last line of the file, it goes through the loop and then it tries to read once more. It is this last attempt to read that generates end-of-file condition and the empty $REPLY.
read < file; echo $REPLY
By default, read reads one line at a time. You only ask for one line so that is what is in $REPLY. (If one specifies the -d option to read, then $REPLY could have the whole file in it depending on the chosen delimiter.
cat file | read; echo $REPLY
This is a pipeline. This means that read is in a subshell. Therefore, shell variables that it creates do not survive.
If your goal is to get the last line of the file into a variable, there are options. For example:
reply="$(tail -n1 file)" ; echo $reply
Or,
reply="$(sed -n '$p' file )" ; echo $reply
(In sed-speak, $ means the last line of the file and p means print. So, $p means print the last line of the file.)
If you want to keep last line from file in REPLY variable using a while loop use this:
REPLY=
while read -r line; do
REPLY="$line"
done < file
echo "REPLY=$REPLY"
