How can I get diff to show only added and deleted lines

"I'm not sure this is possible as it will be hard to differentiate between changed, added and deleted lines.

Consider this file:

start
old
old
old
end

We edit it so it looks like this:

start
old
old but now new
new
new
end

If we diff it we get this output:

< old
< old
---
> old but now new
> new
> new

This is straightforward to generate. But if you ask diff to only print added and deleted line I think it becomes a matter of opinion which lines have been added and deleted and which have been changed. For example, did I delete the the last line that said old and replace it with a line that said new or did I edit it?"

"I had the same question. This function was my solution to obtain the maximum change line number (i.e. changes start with the letter '+'). After which I then loop through the diff file again line by line and do not send to the line processor until this triggers the line to process:

#====================================================================
proc_diff_file() # processes a diff file
#====================================================================
# Arg_1 = Diff File Name
# Arg_2 = New File Name - the one with the new lines
{
NEW_FILE=$1
A_FILE=$2
if [ -f ""$A_FILE"" ]; then
echo ""processing diff $A_FILE""
pre_process_diff $A_FILE
# Set loop separator to end of line
ndx=0
BAKIFS=$IFS
IFS=$(echo -en ""\n\b"")
exec 3<&0
exec 0<$A_FILE
while read line
do
ndx=$(expr $ndx + 1)
# use $line variable to process line in processLine() function
if [ $ndx > $max_ndx ]; then
proc_age $line
fi
done
exec 0<&3
# restore $IFS which was used to determine what the field separators are
IFS=$BAKIFS

# cleanup $NEW_FILE

echo ""processing diff $A_FILE done""
fi
}

Here is the function:

#====================================================================
pre_process_diff() # pre-processes a diff file for last changed line
# sets a variable named $max_ndx
#====================================================================
# Arg_1 = Diff File Name
{
A_FILE=$1
max_ndx=
# collect last line number of diff +
# all lines following are new data
`grep -n ""^[+]"" $A_FILE | gawk '-F:' '{ print $1 }' >tmp`
# Set loop separator to end of line
# read through to the last line number
BAKIFS=$IFS
IFS=$(echo -en ""\n\b"")
exec 3<&0
exec 0<tmp
while read last_line
do
max_ndx=$last_line
done
exec 0<&3
# restore $IFS which was used to determine what the field separators are
IFS=$BAKIFS
echo ""pre-processing diff $A_FILE done max_ndx=$max_ndx""
}

Steve"