Match any repetitive pattern using tcl - regex

Question

I have a binary file that I don't know what is inside. Then, I convert it to hex number using binary scan $bin_data "H*" hex_data. The problem is how to match for any repetitive pattern (byte).
Example 1:
In the file: 0cabab79
Expected Output: abab
Example 2:
In the file: 0c1f1f03035d
Expected Output: 1f1f0303
Example 3:
In the file: 0c678967895d13
Expected Output: 67896789

Answer 1

You can use a more flexible regexp to get all the repeated patterns (at least 2 characters):
set inputs [list 0cabab79 0c1f1f03035d 0c678967895d13]
foreach input $inputs {
set out ""
foreach {whole sub} [regexp -all -inline {(..+)\1} $input] {
append out $whole
}
puts $out
}
# Output:
# abab
# 1f1f0303
# 67896789
If you want to make sure the pattern are in pairs of even number of characters (i.e. aaaaaa should give aaaa and not aaaaaa), then...
set inputs [list 0cabab79 0c1f1f03035d 0c678967895d13 aaaaaa]
foreach input $inputs {
set out ""
foreach {whole sub} [regexp -all -inline {((?:..)+)\1} $input] {
append out $whole
}
puts $out
}
# Output:
# abab
# 1f1f0303
# 67896789
# aaaa

Answer 2

You can do this with a regexp using a backreference:
regexp -all -inline {(..)\1} 0c1f1f03035d
This will return you a list containing the full-length repetition followed by the repeated element for all matches.
So for this one you would get
1f1f 1f 0303 03
Looping through these you can build your Expected Output e.g.
set op {};
foreach {rep sing} [regexp -all -inline {(..)\1} 0c1f1f03035d] {
append op $rep
}