Merge numbered files with variable names [closed] - bash

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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