A OneLiner? is a script (written in, for instance, shell or perl) that fits onto a single line. For instance you could type:
"ls -ls | sort -n"
to sort your files by size (Unix/Linux). Or you could type:
"perl -ane '$tot += $F[3]'; END { print $tot;}"
to print the total of the 4th whitespace-separated field from the standard input.
I've always been fond of the following SedLanguage one liner:
GThat's right. Just one "G". It double spaces the input. See http://sed.sourceforge.net/sed1line.txt for more OneLiners in SedLanguage.