Experience
One senior software engineer tole me Linux system is a life skill for programmer. I have been learning linux command for a while. But I just use linux command to compile, makefile, SSH etc. This exercise make me learn another cool things about Linux. I learn more knowledge about shell command. In challenge 4, I try meself then I found I got a wrong answer before.
Challenge
C1
sort will sort character by character. But if we use sort -n, it will consider string numerical value as a whole.
C2
wc -l < mydata.dat: wc reads from standard outpus which comes from mydata.adt.
wc -l mydata.dat: wc gets a command line parameter telling it to open mydata.dat and get the output result.
C3
uniq is faster when handleing large scale data set, it compare line by line ,so it just remove adjacent duplicated lines.
The command uniq -u will Print only Unique Lines. OR we can sort salmon.txt| uniq to remove all duplicated lines.
C4
head -5 get the first 5 lines in animals.txt:
2012-11-05,deer
2012-11-05,rabbit
2012-11-05,raccoon
2012-11-06,rabbit
2012-11-06,deer
tail -3 get the last three lines of the 5 lines above:
2012-11-05,raccoon
2012-11-06,rabbit
2012-11-06,deer
sort -r > final.txt resversed sort the outcome and save the results to final.txt. So finally, in final.txt, the result is:
2012-11-06,rabbit
2012-11-06,deer
2012-11-05,raccoon
C5
cut -d, -f 2 animals.txt | sort | uniq