SILShack Spring 2014

This exercise was useful for seeing how you can build more complex command pipelines in Unix using fairly simple commands. Learning how to call the manual for each command was also very helpful for understanding how a command behaves by default and how you can modify a command. It was also a useful exercise for learning how input and output works in command line. Nothing in this exercise was particularly challenging, but it was a good exercise for building my knowledge and comfort-level with working in command line.

Challenge Questions

1. When running sort on the original file, the program is sorting by characters. By adding -n we are telling the program to sort the values as numerical values.

2. In wc -l < mydata.dat we are telling the program to take the standard input from the mydata.dat file. Whereas, wc -l mydata.dat is using a command line parameter to tell the program what file to open and perform word count.

3. Adjacent duplicated lines in datasets could be a sign of data entry mistakes, so it is useful for the uniq command to simply remove all duplicates that are adjacent to each other. By adding the sort command, one could first put the lines in alphabetical order and then use uniq to remove duplicates with this final command: sort salmon.txt | uniq. This is another sign of how UNIX allows you to build more complex commands by combining simple commands using pipes.

4. The first pipe cat animals.txt tells the program to concatenate all the files and since this is a single file it simply sends the contents of the file (output) to the next pipe as its input. The head -5 takes the first 5 lines of the file, and tail -3 takes the last three lines of these 5 lines, then sort –r sorts these three lines and then returns the results in reverse order. These three lines are then redirected into the temporary final.txt file instead of being printed as standard output. Essentially, the final.txt file should contain line 3, 4, and 5 from animals.txt sorted in reverse order.

5. You could add sort to put the animal names in order and then use uniq to remove duplicates so the final command would be: cut –d, -f 2 animals.txt | sort | uniq.