Sed one-liner to delete any line that begins with a digit

Quite a few ways. Think negatively:

sed '/[a-z]/!d'    # !x runs x if the pattern doesn't match
grep -v '[a-z]'    # -v means print if the regexp doesn't match
awk '!/[a-z]/'     # !expr negates expr

You should not believe them if they tell you it cannot be done. You should believe them, however, if they tell you it's not easy.

sed '\|*/|!{ s|/\*|\n&|              #if ! */ repl 1st /* w/ \n/*
     h;      s|foo|bar|g;/\n/!b      #hold; repl all foo/bar; if ! \n branch
     G;      s|\n.*\n||;:n           #Get; clear difference; :new label
     n;      \|*/|!bn;s|^|\n/*|      #new line; if ! */ branch new label
     };s|*/|\n&|g                    #repl all */ w/ \n*/
       s|foo|&\nbar|g;:r             #repl all foo w/ foo\nbar
       s|\(/\*[^\n]*\)\nbar|\1|g;tr  #repl all /*[^\n]*\nbar w/ foo
       s|foo\n\(b\)|\1|g             #repl all foo\nbar w/ bar
       s|^\n/.||;s|\n||g             #clear any \n inserts
'    <<\INPUT
asfoo   /* asdfooasdfoo


asdfasdfoo
asdfasdfoo
foo */foo /*foo*/ foo
/*.
foo*/
foo
hello

INPUT

OUTPUT

asbar   /* asdfooasdfoo


asdfasdfoo
asdfasdfoo
foo */bar /*foo*/ bar
/*.
foo*/
bar
hello