Can anyone help me pls? I want to add a text into the middle of file.
I've writtenthe following script

text to add="$1"
file="$2"
lines=$(wc -l $2)
half_lines=$(expr $lines / 2)
head -$half_lines $2 > temp
echo "text to add" >> temp
((half_lines=$half_lines + 1))
tail -$half_lines $2 >> temp
mv temp $2

it gives me `expr : syntax error

Can someone tell me what i did wrong. Was i not to use expr command?