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15 Cards in this Set
- Front
- Back
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What does "last" do?
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It shows logins, in reverse chronological order
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What are the 3 reasons filters are important?
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The output from a command may be very large, filters may reduce & refine the result Organizing data Reformatting |
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What is the general definition of a Filter?
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-receives input from stdout of cmd's -transforms output -writes output to stdout or through redirection |
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What does ls | wc -l do?
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counts the number of files in the directory
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what does wc -l abc.txt do?
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Counts # of lines in file abc.txt
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What longer method can do the same as ls | wc -l?
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ls > tempfile wc -l tempfile rm tempfile |
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What do pipes do that sets them apart from Redirection? (even though pipes are technically a form of redirection)
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They send output from a Unix command to another Unix command Redirect sends thing between files and screen |
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What does head do?
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It outputs the first part of files head [options] filename -cn (print the first n characters) -n (print first n lines) |
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What does tail do?
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Outputs the last part of files same usage as head |
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What does more do?
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displays files on a page-by-page basis -n number of lines to show -d prompt to continue |
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What does less do?
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Similar to more, but with more options
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What does sort do?
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Sorts lines of text [files] Format: sort [options] -t: -k 5,5 uses colon as field delimiter and sorts on the 5th field. -nu sorts numerical order |
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What does uniq do?
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removes duplicate adjacent lines from a file. uniq [options] filename -c : count the instances -d : print only the duplicates (once) -u : print only the unique lines -n : ignore first n fields ex. sort abc | uniq -c # |
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What does wc do?
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prints the number of newlines, words, and characters in files wc [options] filename -c : lines -w : words -l : characters |
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What does cut do?
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Removes columns or fields from a file cut [options] filename -c list : list of columns to cut -f list : list of fields to cut -d char : the delimiter for fields. Only one delimiter may be specified (tab is default) -s : suppress lines without delimiters |
