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sed

Tool for doing stuff with lines, or perhaps stream of characters..

Using as regex to get stuff

By default, everything that is not deleted (by a delete command) is printed to stdout. To inhibit this, pass '-n' flag.

sed '/actual pattern/command'
 
# ex
sed '/Matches this string/p' # command p is printed. But since -d flag is not provided, so will everything else too
 
sed -n '/Matches this string/p' # Only prints rows containing "Matches this string"