Solução alternativa feia testada no Ubuntu Apache / 2.4.18, usando o subconjunto suportado do sed:
$ cat tmp
line3
$ sed "h;s/.*/line1/;p;s/.*/line2/;G;p;s/.*/line4/" tmp
line1
line2
line3
line4
$ cat week
sunday
wednesday
friday
$ sed "2{h;s/.*/monday/;p;s/.*/tuesday/;G;p;s/.*/thursday/;n;p;s/.*/saturday/;}" week
sunday
monday
tuesday
wednesday
thursday
friday
saturday
these work too as \n is still recognised in search string
"G;H;g;s/\n/line1&line2&/;s/\n$/&line4/"
"2{G;H;g;s/\n/monday&tuesday&/;s/\n$/&thursday/;n;p;s/.*/saturday/;}"
$ #sudo a2enmod sed
$ #apache2.conf
<Location /txt/>
AddOutputFilter Sed txt
OutputSed "G;H;g;s/\n/line1&line2&/;s/\n$/&line4/"
</Location>
$ service apache2 reload
$ wget localhost/txt/tmp.txt -qO -
line1
line2
line3
line4
$ #sudo a2enmod ext_filter
$ #apache2.conf
ExtFilterDefine external_sed mode=output intype=text/plain cmd="/bin/sed :0;N;$!b0;s/\n//g"
<Location /txt/>
SetOutputFilter external_sed
</Location>
$ service apache2 reload
$ wget localhost/txt/week.txt -qO -
sundaywednesdayfriday
Veja também: # 1 , #2