mjhjmtu

What will be an "elegant" one-line way to append a single line of data into the end of a file, with herestring, if this exact data isn't already in that file?

This is my herestring append pattern:

cat >> /var/www/html/myFile <<< "myOutput"

Assuming that you want "myOutput" to be a full line
at the last line of the file:

s="myOutput"; sed '$ /^'"$s"'$/b; s/$/n'"$s"'/' file

s="myOutput" Set pattern to match
sed use sed
$ …' file On the last line of the file
/^'"$s"'$/b Match the pattern as a whole line and branch to end if matched.
s/$/n'"$s"'/ If no match, append the pattern at the end line.

If the file already contains the "myOutput" data
somewhere other than the last line,
this will add another copy of it at the end of the file.

s="myOutput"; grep -Fxqe "$s" < "$file" || printf "%sn" "$s" >> "$file"

In below script will check in complete last line for whether variable i present or not if not it inserts variable i in last line of file.

As tested it worked fine

#!bin/bash
i="praveen"
f=$(sed -n '$p' p.txt | sed -n "/^$i$/p")
if [[ -z $f ]]
then
sed "$s/.*/&n$i/g" p.txt
else
echo "output exsists"
fi