Removing new line after a particular text via bash/awk/sed/perl

Question

I would like to remove all the newline character that occurs after a partiular string and replace it with a tab space. Say for instance my sample.txt is as follows

foo
bar bar bar bar some text

I would like it to be

foo    bar bar bar bar some text

How do I do this via bash/awk/sed. Do help.

Answer 1

In awk:

awk '/foo$/ { printf("%s\t", $0); next } 1'

Answer 2

Here is how:

cat input.txt | sed ':a;N;$!ba;s/foo\n/foo\t/g'

More about why simple sed 's/foo\n/foo\t/g' does not work here: http://linuxtopia.org/online_books/linux_tool_guides/the_sed_faq/sedfaq5_009.html

Answer 3

perl -pe 's/(?<=foo)\n/\t/' input