Replace the first line in a text file by a string

I am a newbie at shell scripting, and am confused about how to use sed or any other tools to replace the first line in my text file by a string. Here are the text file contents:

/home/snehil/Desktop/j1/movie.MOV
"spome other text lines'

I want to replace the first line (movie file path) with just movie.MOV (could be a variable in the shell script)

Please guide me how to do this. I came across sed in some posts, do I need to use sed here?

sed is the right tool, try doing :

var="movie.MOV"
sed -i "1s/.*/$var/" file.txt

explanations

• 1 mean first line
• the rest is the substitution s/// : we substitute everything (.*) by the $var variable

You can do this easy with tail:

#I want to replace the first line
cp test.txt test.txt.backup
echo 'mynewfirstline'> test.txt
#add everything from old file starting from second line
cat test.txt.backup |tail -n+2>> test.txt