For example, file1 contains:
entry1:value1
entry2:value2
entry3:value3
Now I want to add a prefix "file1:" to each line:
file1:entry1:value1
file1:entry2:value2
file1:entry3:value3
How can I do that in one command line?
I'm using Bash.
BTW, the leading space must be preserved, so the Bash built-in read line doesn't work for me.