compare numbers within a string

[desp_to_learn]

hi everyone,
i want to compare two lists of files. i want to check which file in List A is not in list B.this is how the lists are;
List A List B
file21.txt file21.txt
file23.txt file 22.txt
file24.txt file23.txt
file25.txt file24.txt

so i want the program to tell me that file22.txt is missing from list A.
does anybody have idea on how i can program this? help please.
thank u.

[wje_lf]

No need to program anything. Do this at the command line:

man diff

and all will be revealed.

[desp_to_learn]

thank you for your prompt reply.

[desp_to_learn]

About diff and grep command. I am now trying to write a script to compare two files by using diff command and i grep the changes in each line and then count the those lines.
I use this command
diff fileA fileB | grep -e '^c[1-9]' | wc -l

the problem is when there is consecutive changes in two files the output is combined as
$diff fileA fileB | grep -e '^c[1-9]'
c3 10
and hence i get when i count the lines it gives 1
$diff fileA fileB | grep -e '^c[1-9]' | wc -l
1
i would like to count the ocurrence of the changes.In this case i expect the grep output to be
c3
c4
c5 etc.
and when i count them lines i want to have
$diff fileA fileB | grep -e '^c[1-9]' | wc -l
8

please help!

[wje_lf]

How about this?

#!/bin/bash

cat > 4a.txt <<EOD
aaa
bbb
ccc
ddd
eee
EOD

cat > 4b.txt <<EOD
aaa
bbb
eee
fff
ggg
hhh
EOD

diff 4a.txt 4b.txt | grep '^[<>]' | wc -l