How to use `while read` (Bash) to read the last line in a file if there’s no newline at the end of the file?

Question

Let’s say I have the following Bash script:

while read SCRIPT_SOURCE_LINE; do
  echo \"$SCRIPT_SOURCE_LINE\"
done

I noticed that for files

Answer 1

In your first example, I'm assuming you are reading from stdin. To do the same with the second code block, you just have to remove the redirection and echo $REPLY:

DONE=false
until $DONE ;do
read || DONE=true
echo $REPLY
done

Answer 2

The basic issue here is that read will return errorlevel 1 when it encounters EOF, even if it'll still correctly feed the variable.

So you can use errorlevel of read right away in your loop, otherwize, the last data won't be parsed. But you could do this:

eof=
while [ -z "$eof" ]; do
    read SCRIPT_SOURCE_LINE || eof=true   ## detect eof, but have a last round
    echo "$SCRIPT_SOURCE_LINE"
done

If you want a very solid way to parse your lines, you should use:

IFS='' read -r LINE

Remember that:

• NUL character will be ignored
• if you stick to using echo to mimick the behavior of cat you'll need to force an echo -n upon EOF detected (you can use the condition [ "$eof" == true ])

Answer 3

I use the following construct:

while IFS= read -r LINE || [[ -n "$LINE" ]]; do
    echo "$LINE"
done

It works with pretty much anything except null characters in the input:

• Files that start or end with blank lines
• Lines that start or end with whitespace
• Files that don't have a terminating newline

Answer 4

@Netcoder's answer is good, this optimisation eliminates spurious blank lines, also allows for the last line not to have a newline, if that's how the original was.

DONE=false
NL=
until $DONE ;do
if ! read ; then DONE=true ; NL='-n ';fi
echo $NL$REPLY
done

I used a variant of this to create 2 functions to allow piping of text that includes a '[' to keep grep happy. (you can add other translations)

function grepfix(){
    local x="$@";
    if [[ "$x" == '-' ]]; then
      local DONE=false
      local xx=
      until $DONE ;do
         if ! IFS= read ; then DONE=true ; xx="-n "; fi
         echo ${xx}${REPLY//\[/\\\[}
      done
    else
      echo "${x//\[/\\\[}"
    fi
 }


 function grepunfix(){
    local x="$@";
    if [[ "$x" == '-' ]]; then
      local DONE=false
      local xx=
      until $DONE ;do
         if ! IFS= read ; then DONE=true ; xx="-n "; fi
         echo ${xx}${REPLY//\\\[/\[}
      done
    else
      echo "${x//\\\[/\[}"
    fi
 }

(passing - as $1 enables pipe otherwise just translates arguments)

Answer 5

Using grep with while loop:

while IFS= read -r line; do
  echo "$line"
done < <(grep "" file)

Using grep . instead of grep "" will skip the empty lines.

Note:

1. Using IFS= keeps any line indentation intact.

2. You should almost always use the -r option with read.

3. File without a newline at the end isn't a standard unix text file.

Answer 6

This is the pattern I've been using:

while read -r; do
  echo "${REPLY}"
done
[[ ${REPLY} ]] && echo "${REPLY}"

Which works because even tho' the while loop ends as the "test" from the read exits with a non-zero code, read still populates the inbuilt variable $REPLY (or whatever variables you choose to assign with read).