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Solutions to execises in Automating Workflows

Short Exercise

From the data directory, use a single command to view the Subject line of every file in THOMAS and jamesm.

Solution

grep Income THOMAS/* jamesm/*

Short Exercise

Use the echo command and the append operator, >>, to append your name to the file and then sort the output into a new file called Sorted.

Solution

This assumes that there is already a file named toBeSorted that we made with an editor (nano) that contains:

Bob
Alice
Diane
Charles

To add your name to the file:

echo Lauren >> toBeSorted

The file can be sorted into a new file with:

sort toBeSorted > Sorted

Short Exercise

  1. Use the man command to find out how to sort the output from wc in reverse order.

Solution To reverse the order of the sort command you add the -r argument.

  1. Combine the wc, sort, head and tail commands so that only the wc information for the largest file is listed

Hint: To print the smallest file, use:

wc Bert/* | sort -k 3 -n | head -n 1

Solution

It is important to realize that when we are using wc on a set of files Bert/* it will always conclude with a line that is the sum. No matter how we sort this, the largest single file is always either the 2nd line or the 2nd last line.

The above line prints the info for the smallest file because it is the first line. If we wanted the last line:

wc Bert/* | sort -k 3 -n | tail -n 1

but, again, this will be the sum of all the files.

We can get the last 2 lines with:

wc Bert/* | sort -k 3 -n | tail -n 2

and then we can take the first of those lines:

wc Bert/* | sort -k 3 -n | tail -n 2 | head -n 1

Short Exercise

Create an executable script called smallestage in the data directory, that is similar to the smallest script, but prints the file containing the file with the smallest Age. Use the commands grep, sort, and tail to do this.

Solution

We can experiment on the command line to find the right commands. Starting with the command to just get all the "Age" data:

grep Age *

will search for the word "Age" in all the files (*).

Next we can sort this numerically based on the numerical value of the Age, found in the 2nd column:

grep Age * | sort -n -k 2

The smallest age will be the first item in that list:

grep Age * | sort -n -k 2 | head -n 1

Now that we've found this command, we can put it in a script to help us reuse it with less typing, and we'll be less error prone.

We create a new file by opening it with nano

nano smallestage

and putting in the following lines:

#!/bin/bash
grep Age * | sort -n -k 2 | head -n 1

The first line tells the shell what program to use to run this script.

After exiting the editor (Control-X) we can make it executable:

chmod a+x smallestage