Linux : Prefix a string to all rows in a file - sed

Consider, you have a file like below:

# cat test.txt
12324
234523
3431
343
34345
3434
43234

Now, if you want to prefix a particular string to each line in the file, how will you do it? This is a common challenge for DBA/Developers working with Linux environment.


Here's one of the simple way that I follow:

Say, I want to prefix below line:
SELECT * FROM testTab WHERE testCol=

So I do like this:

# cat test.txt | sed "s/^/SELECT * FROM testTab WHERE testCol=/g" > test_prefixed.sql

Now check the output file:

# cat test_prefixed.sql
SELECT * FROM testTab WHERE testCol=12324
SELECT * FROM testTab WHERE testCol=234523
SELECT * FROM testTab WHERE testCol=3431
SELECT * FROM testTab WHERE testCol=343
SELECT * FROM testTab WHERE testCol=34345
SELECT * FROM testTab WHERE testCol=3434
SELECT * FROM testTab WHERE testCol=43234


That's it!