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Ubuntu - File - Print every line in a file matching the regular expression

Print the lines matching the regular expression. (emulates grep).

awk '/regex_here/' filename

Print the lines that don't match the regular expression. (emulates grep -v).

awk '!/regex_here/' filename

Print the line before the regular expression match.

awk '/regex_here/{print x};{x=$0}' filename

Print the line after the regular expression match.

awk '/regex_here/{getline; print}' filename