Question

Say I have a script with a number of lines beginning foobar

I would like to move all of the lines to the end of the document while keeping their order

e.g. go from:

# There's a Polar Bear
# In our Frigidaire--
foobar['brangelina'] <- 2
# He likes it 'cause it's cold in there.
# With his seat in the meat
foobar['billybob'] <- 1
# And his face in the fish

to

# There's a Polar Bear
# In our Frigidaire--
# He likes it 'cause it's cold in there.
# With his seat in the meat
# And his face in the fish
foobar['brangelina'] <- 2
foobar['billybob'] <- 1

This is as far as I have gotten:

grep foobar file.txt > newfile.txt
sed -i 's/foobar//g' foo.txt
cat newfile.txt > foo.txt

Answer 1

This might work:

sed '/^foobar/{H;$!d;s/.*//};$G;s/\n*//' input_file

EDIT: Amended for the corner case when foobar is on the last line