Add a sentence in each line of a file with sed

Question

I have a file with this content:

dog 
cat

and I want to add a sentence (I have a) before every sentence, so the new content should be:

I have a dog
I have a cat

I tried with

sed -i 'I have a ' file

But I get something like this

I have a 
dog
I have a
cat

Which would be the correct use of sed? Is there another way of doing?

Answer 1

You can use sed:

sed -i.bak 's/^/I have a /' file
cat file
I have a dog
I have a cat

Or awk:

awk '{print "I have a", $0}' file
I have a dog
I have a cat

Answer 2

With bash:

while read -r line
do
    echo "I have a $line"
done < file > tmp_file && mv tmp_file file

Basically, read each line and echo them back with the leading title. Then redirect to a temp file. In case the command succeeds, then move the temp file into the original one.

---

With awk:

awk '{print "I have a", $0}' file > tmp_file && mv tmp_file file

---

With sed: check anubhava's answer for the best way. This can be another.

sed -i.bak -n 's/^/I have a /p' file

Note it is good practice to use -i.bak (or -i.whatever) to generate a backup file with the .bak extension.

---

Just for fun, you can also use paste:

$ paste -d" " <(printf "%0.sI have a\n" $(seq $(wc -l <file))) file
I have a dog
I have a cat

Explanation

• paste -d" " file1 file prints two files side by side, with space as delimiter.

• printf "%0.sI have a\n" $(seq $(wc -l <file)) print "I have a" as many times a lines file has.

  $ wc -l <a
  2
  $ seq $(wc -l <a)
  1
  2
  $ printf "%0.sI have a\n" $(seq $(wc -l <a))
  I have a
  I have a
  

Answer 3

sed -i 's/^/I have a /' your_file