Move lines matching a pattern from one file to another

Question

I want to move lines matching certain pattern from file1 to file2. Analogous to operation cut and paste from one file to another in windows

Example

let's say I want to cut all lines containg bar from file1 and paste it into newly created file2

Input:

file1

bla foo bla
bla bar bla
bla aaa bla
bla bar bla
bla foo bla

Desired output after processing:

file1

bla foo bla
bla aaa bla
bla foo bla

file2

bla bar bla
bla bar bla

What I have tried

grep creates desired file2 but doesn't modify file1

grep 'bar' file1 > file2

sed -i modifies desired file1 but doesn't create file2

sed -i '/bar/d' file1

If I execute both commands one after another, I get desired result. But here I am looking for a single line command out of curiosity and to make a script more concise.

Your help would be appreciated.

Answer 1

You can use perl and select a different filehandle based in a match of a regular expression when printing:

perl -i.bak -ne 'BEGIN { open $oh, q|>|, pop or die } { print { m/bar/ ? $oh : q|ARGVOUT| } $_ }' file1 file2

It yields:

==> file1 <==
bla foo bla
bla aaa bla
bla foo bla

==> file2 <==
bla bar bla
bla bar bla

Answer 2

This might work for you (GNU sed):

sed -i -e '/bar/{w file2' -e 'd}' file1

An alternative:

sed -i -e '/bar/w file2' -e '//d' file1

To append to file2, write to a temporary file and use cat to append at the end of file in a bash script, or use:

sed -i -e '/bar/w tmpfile' -e '$e cat tmpfile >> file2 && rm tmpfile' -e '//d' file1

N.B. For the last solution, only one input file can be modified at a time.