Merge numbered files with variable names

Question

I have a number of numbered files, e.g.: alpha_01.txt alpha_02.txt beta_01.txt beta_02.txt I want to execute a single line bash that will output correctly merged files based on their variable name (e.g. alpha, beta, ...), that is, alpha.txt beta.txt.

I can do so for a single file:

cat alpha_*.txt(n) >>alpha.txt 2>/dev/null

But I don‘t know the name before _*.txt. Can I use a wildcard here? Or what would be the best solution?

Answer 1

If you want to concatenate all the alpha_xxx.txt files then you cannot have beta_xxx.txt in the arguments of cat.

As @tripleee said, the easiest way would be to use a for loop where you list all the prefixes:

for name in alpha beta
do
    cat "$name"_*.txt > "$name".txt
done

---

Now, if you don't know the prefixes in advance then you can always workout something with awk:

awk '
    BEGIN {
        for (i = 1; i <= ARGC; i++) {
            filename = ARGV[i]

            if (filename !~ /^(.*\/)?[^\/]+_[0-9]+\.[^\/.]+$/)
                continue

            match(filename, /^(.*\/)?[^\/]+_/)
            prefix = substr(filename, RSTART, RLENGTH-1)

            match(filename, /\.[^.\/]+$/)
            suffix = substr(filename, RSTART, RLENGTH)

            outfile[filename] = prefix suffix
        }
    }
    FILENAME in outfile { print $0 > outfile[FILENAME] }
' ./*.txt