mjhjmtu

I have multiple files .txt which contain names of people sorted alphabetically so for example in main directory I have directory a which contains one a.txt full with names which start with "a" like "Anna" "Andrew" etc. The same thing repeats in main directory I have directory b containing b.txt full with names etc. up until x,y,z. How can I extract the names and create a master.txt containing all people's names?

You can accomplish this by using the cat command and filename expansion. If all of these files are in the source directory /path/to/directory, and there are no other files in this directory, then the most succinct command would be the following:

cat /path/to/directory/*/*.txt > master.txt

This will create a file called master.txt in your current directory which contains the concatenated contents of all of the files in the source directory. NOTE: This will include any files in any of the subdirectories of the source directory.

If there are other files in the directory (or if you just want to be a little bit more precise) then you can use this command instead:

cat /path/to/directory/[a-z]/[a-z].txt > master.txt

This will only match the following files in the source directory:

a/a.txt
a/b.txt
a/c.txt
.
.
.
z/x.txt
z/y.txt
z/z.txt

If there are other files in the source directory, or if you have files of the similar to a/z.txt where the subdirectory name doesn't match the base-name of the file, and if you want to exclude those files, then you would have to use a more precise command to narrow down the list of matched files. In that case you could use brace-expansion and a for-loop:

for letter in a..z; do 
 cat "/path/to/directory/$letter/$letter.txt"; 
done >> master.txt

This will match exactly the files you've specified in your question and no other files.

Replace main_dir with the path to your main directory, save this in a script and run from the terminal as sh ./script-name.sh

#!/bin/bash
for i in $( cd main_dir && ls ); do
 cat "main_dir/$i/$i.txt" >> "master.txt"
done