Exercises. Part 5

• Leah has several hundred data files, each of which is formatted like this:

2013-11-05,deer,5
2013-11-05,rabbit,22
2013-11-05,raccoon,7
2013-11-06,rabbit,19
2013-11-06,deer,2
2013-11-06,fox,1
2013-11-07,rabbit,18
2013-11-07,bear,1

• Write a shell script called species.sh that takes any number of filenames as command-line parameters, and uses cut, sort, and uniq to print a list of the unique species appearing in each of those files separately. (Test this on the files in data/pipes/animals)

• Write a shell script called longest.sh that takes the name of a directory and a filename extension as its parameters, and prints out the name of the most recently modified file in that directory with that extension. For example:

  $ bash largest.sh /tmp/data pdb

  would print the name of the .pdb file in /tmp/data that has been changed most recently.

• If you run the command: history | tail -5 > recent.sh the last command in the file is the history command itself, i.e., the shell has added history to the command log before actually running it. In fact, the shell always adds commands to the log before running them. Why do you think it does this?

• Joel’s data directory contains three files: fructose.dat, glucose.dat, and sucrose.dat. Explain what the following script, example.sh, would do when run as bash example.sh *.dat:

    echo *.*
    for filename in $1 $2 $3
    do
        cat $filename
    done
    echo $*.dat

• The history shows the last thousand or so commands that you’ve used. What does this code do? (Test awk '{print $1}' data/pdb/methane.pdb to see what this awk does.)

    awk '{print $1}' ~/.bash_history | sort | uniq -c | sort -n | tail -10 | sort -n -r