SHELL

sed remove line after match

Use d option at the end of sed command string for deleting line of matches.
sed -i "" "s/matching_pattern/,+1 d" file.txt #+1 defines number of lines
# to delete after matching line

sed delete line before match

Use d option at the end of sed command string for deleting line of matches.
tac | sed -i "" "s/matching_pattern/I+1 d" file.txt | tac #

sed delete line match

sed '/pattern to match/d' ./infile

delete strings after match to eol using sed command

$ cat file | awk -F '.com' '{print $1".com"}'
google.com
unix.stackexchange.com
isuckatunix.com

delete strings after match to eol using sed command

# To explicitly delete everything that comes after ".com", just tweak your existing sed solution to replace ".com(anything)" with ".com":
sed 's/.com.*/.com/' file.txt

delete strings after match to eol using sed command

# You can use awk's field separator (-F) following way:
$ cat file
google.com/funny
unix.stackexchange.com/questions
isuckatunix.com/ireallydo