gc log.txt | select -first 10 # head
gc -TotalCount 10 log.txt # also head
gc log.txt | select -last 10 # tail
gc -Tail 10 log.txt # also tail (since PSv3), also much faster than above option
gc log.txt | more # or less if you have it installed
gc log.txt | %{ $_ -replace '\d+', '($0)' } # sed