Lab 5: glob, loops, shift

Questions

1. Your friend has sent you more game data in updated_cool_online_game.csv. Which players have improved their scores?

diff cool_online_game.csv updated_cool_online_game.csv

2. The following questions make use of globbing
   1. List all files in /bin that start with the letter g

   ls /bin/g*

   2. List all files in /bin that end with the letter t

   ls /bin/*t

   3. List all files in /bin that start with the letter g and end with the letter t, where the second letter is not e

   ls /bin/g[^e]*t

3. Write a script texter.sh that accepts any number of command line arguments. It should create a text file using the first argument as the file name and the second argument as the file content. Repeat for all remaining arguments. If there is an odd number of arguments, leave the last file blank.

   > ./texter.sh f1 "this is file 1 content" f2 "deadbeef"
   > ls
   
   f1 f2
   
   > cat f1
   
   this is file 1 content
   
   > cat f2
   
   deadbeef
   

   #!/bin/bash
   
   while [[ $# -gt 0 ]]
   do
       echo $2 > $1
       shift
       shift
   done
   

4. Write a script sizes.sh which prints stats about each file in the current directory. For each file it should print the filename and file size After printing data for all files, print the size and name of the largest file, then print the sum of all the file sizes. Your script should ignore directories. Hint: You can obtain the size of a file as a number by using wc -c with cut

   > ./sizes.sh
   160786 Alice_in_Wonderland.txt
   448821 Frankenstein.txt
   2525 cool_online_game.csv
   363 sizes.sh
   4320 lots_of_the.txt
   2549 updated_cool_online_game.csv
   Largest is 448821 in Frankenstein.txt
   Sum is 619364
   

#!/bin/bash

sum=0
max_size=0
max_name=''

for f in *
do
    if [[ -f $f ]]
    then
        size=$(wc -c $f | cut -f1 -d " ")
        echo "$size $f"
        if [[ $size -gt $max_size ]]
        then
            max_size=$size
            max_name=$f
        fi
        sum=$((sum + size))
    fi
done
echo "Largest is $max_size in $max_name"
echo "Sum is $sum"

5. Modify sizes.sh to accept the command line options as specified below. Use shift and case to achieve this:

   -d DIRECTORY Count files in DIRECTORY instead of .
   
   -h Display this help message and exit
   #!/bin/bash
   
   sum=0
   max_size=0
   max_name=''
   dir='.'
   
   
   while [[ $# -gt 0 ]]
   do
       case $1 in
     -h) echo -d DIRECTORY Count files in DIRECTORY instead of .
           echo
           echo -h Display this help message and exit
           exit 0;;
     -d) if [[ -z $2 ]]
           then
               echo "Missing operand for -d argument"
               exit 1
           fi
           dir=$2
           shift;;
     *) echo "Unknown argument $1"
           exit 2;;
       esac
       shift
   done
   
   for f in $dir/*
   do
       if [[ -f $f ]]
       then
           size=$(wc -c $f | cut -f1 -d " ")
           echo "$size $f"
           if [[ $size -gt $max_size ]]
           then
               max_size=$size
               max_name=$f
           fi
           sum=$((sum + size))
       fi
   done
   echo "Largest is $max_size in $max_name"
   echo "Sum is $sum"
   

   You can definitely improve on this, for instance by cleaning up the output and checking if wc falls over.
6. When would you prefer a while loop over a for loop? When would you prefer a for loop? What is a danger of using a while loop?
While loops are good when you will be looping for an indeterminate amount of time (eg until a variable changes, while waiting for another process, or while waiting for user input). For loops are good for looping over a fixed set of data or a fixed range of numbers. While loops require you to manually update the loop condition, otherwise you can get stuck in an infinite loop.

Bonus

-r Instead of ignoring directories, recursively run stats.sh in each directory found.

Department of Computer Science & Software Engineering The University of Western Australia Last modified: 26 April 2023 Modified By: Michael Wise