in reply to Merge pairs of lines

Not for big files 

C:\test>type junk
A
B


C

D

C:\test>perl -0pe"y/\n//s;s/(.+)\n(.+)/$1,$2/g" junk
A,B
C,D

[download]

Examine what is said, not who speaks.

The 7th Rule of perl club is -- pearl clubs are easily damaged. Use a diamond club instead.

In Section Cool Uses for Perl