Formatting Output From Shell Script

Question

I am working on a shell script that takes stdin or file as input and prints the averages and medians for rows or columns depending on the arguments.

When calculating the averages for the columns, the output needs to print out the following (tabbed):

My output currently looks like this (no spaces or tabs):

Averages:

92480654263

Medians:

6368974

Is there a way to echo out the averages and medians with tabs so each average and median set align left correctly? Here is a sample of how I am printing out the averages:

echo "Averages:"
        while read i
        do
            sum=0
            count=0
            mean=0
            #Cycle through the numbers in the rows
            for num in $i
            do
                #Perform calculations necessary to determine the average and median
                sum=$(($sum + $num))
                count=`expr $count + 1`
                mean=`expr $sum / $count`
            done
            echo -n "$mean"
        done < $1

Why are you using `expr` when you can (and do elsewhere) use `$((...))`? — chepner, Apr 22 '17 at 22:04
off-topic: rename the variable `i` into `line`, that makes the code easier ti understand (calculate the mean for each line). — Walter A, Apr 22 '17 at 22:30

score 1 · Answer 1 · answered Apr 22 '17 at 21:24

1

man echo:

   -e     enable interpretation of backslash escapes

   If -e is in effect, the following sequences are recognized:

   \t     horizontal tab

I'd try echo -n -e "$mean\t", didn't test it though.

answered Apr 22 '17 at 21:24

James Brown

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score 1 · Answer 2 · answered Apr 22 '17 at 22:08

You should use printf. For instance, this will print a value followed by a tab

printf "%s\t" "$mean"

You can actually print several values separated by tabs if you want by adding arguments :

printf "%s\t" "$mean" "$count"

You can use an array expansion to print several values separated by tabs :

printf "%s\t" "${my_array[@]}"

Among advantages of printf over echo is the availability of flexible formatting strings, and the fact that implementations of printf vary less than those of echo among shells and operating systems.

score 0 · Answer 3 · answered Apr 23 '17 at 10:41

You could try using column command but it does take additional steps:

echo "Averages:"

while read line
do
    sum=0
    count=0
    mean=0
    #Cycle through the numbers in the rows
    for num in $line
    do
        #Perform calculations necessary to determine the average and median
        (( sum += num ))
        (( count++ ))
        (( mean = sum / count ))
    done
    (( mean == 0 )) && out=$mean || out="$out|$mean"
done < $1

echo "$out" | column -s'|' -t

Above is untested as I do not have the original file, but you should get the idea. I would add that the division will also provide truncated values so not exactly accurate.

Formatting Output From Shell Script

3 Answers3