Grep

filter huge files for relevant parts

You constantly get files of which only a small part is relevant! grep is the tool you need to squeeze millions of lines of data and keep only the essence.

# grep can be used in keep-mode to retain only what patches the filter
$ grep "my-pet-name" huge_list_of_animals.txt
 
# but also in trim-mode to exclude unwanted lines
$ grep -v "dinosaurs" huge_list_of_animals.txt
 
# and as always, the unix pipe is there to bless a perfect union
# !! apply first the filter that will shrink your input the most for speedup
$ grep "my-pet-name" huge_list_of_animals.txt | grep -v "dinosaurs"
 
# which is the same as
$ grep -v "dinosaurs" huge_list_of_animals.txt | grep "my-pet-name"

Note: grep can also count instead of returning results, just add -c to the command. Finally, zgrep will do on archives.

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