Command line - save sub-strings conditionally

Question

Can a command line utility save sub-strings conditionally in different files? I have a file (file.txt) with several lines like the following.

1/1_ABCD4.txt:20020711
1/1_ABCD10.txt:20020731
2/2_ABCD2.txt:20071103
2/2_ABCD5.txt:20071107
3/3_ABCD1.txt:20090225
3/3_ABCD3.txt:20090230

My goal is to save 20020711 together with 20020731 in file 1, 20071103 with 20071107 in file 2, and 20090225 with 20090230 in file 3?

I could extract the desired sub-strings after : with the following command, but would lose the reference digit by doing so:

$ grep -oP 'txt\:\K[A-Z0-9-]+' 'path/to/file.txt'

20020711
20020731
20071103
20071107
20090225
20090230

Is it possible to build three separate files with the first digit before / as target reference while using command line? The destination might be the same directory like the original text file.

1. File:

20020711
20020731

2. File:

20071103
20071107

3. File:

20090225
20090230

Thank you.

Answer 1

With awk:

awk -F'[:/]' '{print $NF > $1}' file

We split the row using both / and : as separators. The last field ($NF) is what to print, and the first field ($1) is the output filename.

---

After running for your test input file:

$ head 1 2 3
==> 1 <==
20020711
20020731

==> 2 <==
20071103
20071107

==> 3 <==
20090225
20090230

---

Also, depending on your data, it is good to add a condition before this action, to avoid printing to a file with a random name, in case we have more lines with different structure, the input could be dangerous.

A simple example, if we want to print only when the first field (the filename) has only digits:

awk -F'[:/]' '$1 ~ /^[0-9]+$/ {print $NF > $1}' file

Answer 2

Using sed

$ sed s'~\([0-9]\)/[^:]*:\(.*\)~echo \2 >> \1~e' file.txt

$ cat 1
20020711
20020731