zero-padding and sorting - Linux Shell Scripting

Question

I am trying to do some text file manipulation in Linux.

I have a file, called names.txt that looks like this:

A1
X12
B4
Y5
C10
Z23
B8
C3
Z6

And I need it to look like this:

A01
B04
B08
C03
C10
X12
Y05
Z06
Z23

GOAL: I need to zero-pad the single digits and then alphabetize the results, and save to file sorted_names.txt

I'm thinking I need to count the number of characters per line first, and if the number of characters is less than 2, then add a zero. Lastly I would need to sort alphabetically.

For starters, I think I do this to count the number of characters per line:

cat names.txt | while read line
do

  count=$(echo $line | wc -c)
  echo $line $count

done

Then my thought was to loop through count:

for COUNT in $count
if [( $COUNT = "3" )];
then
    echo doZeroPadHere
fi

Answer 1

Is it important to you to do it using only built-in Bash features? Because it seems easier to use sed and sort:

<names.txt sed 's/^\([A-Z]\)\([0-9]\)$/\10\2/' | sort >sorted_names.txt

Answer 2

Here's a solution using only Bash and sort:

while read line
do 
    printf "%s%02d\n" ${line:0:1} ${line:1}
done <names.txt | sort >sorted.txt

This reads lines from names.txt, and splits each one up into its first character (${line:0:1}) and the rest of the line after the first character (${line:1}). It uses printf (more details) to print the first character verbatim, and the rest of the line as a 0-padded number. It redirects its input from names.txt (avoiding a useless use of cat), pipes the output to sort, and redirects that into sorted.txt.

Answer 3

Here's one way using awk and sort:

awk '{ printf "%s%02d\n", substr($0,0,1), substr($0,2) | "sort" }' file

Results:

A01
B04
B08
C03
C10
X12
Y05
Z06
Z23

Answer 4

Here's a Perl way to do it:

perl -lpe's/^([A-Z])(\d)$/${1}0$2/' names.txt

For each line, if it matches exactly one letter and one digit, change it to the letter, a zero, and the digit. Then print.