Cannot Be Done

I'm sorry, but this “problem” is truly impossible to solve. Consider these:

• ꜰᴜᴄᴋ   is U+A730.1D1C.1D04.1D0B, "\N{LATIN LETTER SMALL CAPITAL F}\N{LATIN LETTER SMALL CAPITAL U}\N{LATIN LETTER SMALL CAPITAL C}\N{LATIN LETTER SMALL CAPITAL K}"
• ᶠᵘᶜᵏ   is U+1DA0.1D58.1D9C.1D4F, "\N{MODIFIER LETTER SMALL F}\N{MODIFIER LETTER SMALL U}\N{MODIFIER LETTER SMALL C}\N{MODIFIER LETTER SMALL K}"
• 𝒻𝓊𝒸𝓀   is U+1D4BB.1D4CA.1D4B8.1D4C0, "\N{MATHEMATICAL SCRIPT SMALL F}\N{MATHEMATICAL SCRIPT SMALL U}\N{MATHEMATICAL SCRIPT SMALL C}\N{MATHEMATICAL SCRIPT SMALL K}"
• 𝖋𝖚𝖈𝖐   is U+1D58B.1D59A.1D588.1D590, "\N{MATHEMATICAL BOLD FRAKTUR SMALL F}\N{MATHEMATICAL BOLD FRAKTUR SMALL U}\N{MATHEMATICAL BOLD FRAKTUR SMALL C}\N{MATHEMATICAL BOLD FRAKTUR SMALL K}"
• 𝓕 𝒰 𝒞 𝒦   is U+1D4D5.1D4B0.1D49E.1D4A6, "\N{MATHEMATICAL BOLD SCRIPT CAPITAL F}\N{MATHEMATICAL SCRIPT CAPITAL U}\N{MATHEMATICAL SCRIPT CAPITAL C}\N{MATHEMATICAL SCRIPT CAPITAL K}"
• ⓕ ⓤ ⓒ ⓚ   is U+24D5.24E4.24D2.24DA, "\N{CIRCLED LATIN SMALL LETTER F}\N{CIRCLED LATIN SMALL LETTER U}\N{CIRCLED LATIN SMALL LETTER C}\N{CIRCLED LATIN SMALL LETTER K}"
• Γ̵𐌵ᏟᏦ   is U+393.335.10335.13DF.13E6, "\N{GREEK CAPITAL LETTER GAMMA}\N{COMBINING SHORT STROKE OVERLAY}\N{GOTHIC LETTER QAIRTHRA}\N{CHEROKEE LETTER TLI}\N{CHEROKEE LETTER TSO}"
• ƒμɕѤ   is U+192.3BC.255.464, "\N{LATIN SMALL LETTER F WITH HOOK}\N{GREEK SMALL LETTER MU}\N{LATIN SMALL LETTER C WITH CURL}\N{CYRILLIC CAPITAL LETTER IOTIFIED E}"
• Г̵ЦСК   is U+413.335.426.421.41A, "\N{CYRILLIC CAPITAL LETTER GHE}\N{COMBINING SHORT STROKE OVERLAY}\N{CYRILLIC CAPITAL LETTER TSE}\N{CYRILLIC CAPITAL LETTER ES}\N{CYRILLIC CAPITAL LETTER KA}"
• ғᵾȼƙ   is U+493.1D7E.23C.199, "\N{CYRILLIC SMALL LETTER GHE WITH STROKE}\N{LATIN SMALL CAPITAL LETTER U WITH STROKE}\N{LATIN SMALL LETTER C WITH STROKE}\N{LATIN SMALL LETTER K WITH HOOK}"
• ϜυϚΚ   is U+3DC.3C5.3DA.39A, "\N{GREEK LETTER DIGAMMA}\N{GREEK SMALL LETTER UPSILON}\N{GREEK LETTER STIGMA}\N{GREEK CAPITAL LETTER KAPPA}"
• ЖↃUᆿ   is U+416.2183.55.11BF, "\N{CYRILLIC CAPITAL LETTER ZHE}\N{ROMAN NUMERAL REVERSED ONE HUNDRED}\N{LATIN CAPITAL LETTER U}\N{HANGUL JONGSEONG KHIEUKH}"
• ʞɔnɟ   is U+29E.254.6E.25F, "\N{LATIN SMALL LETTER TURNED K}\N{LATIN SMALL LETTER OPEN O}\N{LATIN SMALL LETTER N}\N{LATIN SMALL LETTER DOTLESS J WITH STROKE}"

It Gets Worse

And if you think those are easy, just try coping with all of these:

𝓕 00 Ↄ ʞ, F ᵾ ⒞ Ｋ, K ⓒ Ц ⒡ , 𝖋 𝖀 K 𝒸, ғ ∞ Ϛ k, f 𝓊 Ꮯ K, ⓕ oo ɔ ⓚ , ɟ ⒰ ¢ Ｋ, 𝒻 𝖚 ȼ 𝖐, 𝕱 Ù ȼ ⒦ , f 𝒰 ⒞ ƙ, Ｆ 𐌵 ᶜ 𝕶, Ｆ ∞ 𝒞 Ж , 𝕱 @ Ꮯ 𝓀, ɟ ᵘ 𝒞 𝕶, Ｆ Ц ¢ 𝒦, f oo Ꮯ ʞ, 𝕱 oo ¢ Ж , 𝕱 υ ᶜ Κ , Ϝ ú * ʞ, ꜰ 𝖚 c K, ƒ ᵘ ȼ k, 𝖋 U ȼ 𝕶, Ж ɔ μ ƒ, Ｆ ⓤ ⒞ k, ƒ 𝖚 C ƙ, ғ 00 ɔ Ѥ, ƒ Ｕ c ᴋ, 𝕱 ∞ Ꮶ ⓒ , ꜰ 𝓊 ᴄ ⒦ , 𝕱 ⒰ Ꮯ Ѥ, ꜰ ᴜ 𝒞 ⒦ , Ｆ 𝒰 𝖈 ʞ, f 00 𝖈 𝓀, ғ u С K, f 𐌵 ɔ Κ , f μ Ↄ K, ɟ 𝖚 c ʞ, f 𝖚 Ↄ 𝖐, F μ ¢ 𝓀, ᆿ 𝖀 ᴄ ⒦ , Κ ¢ oo ɟ, ᶠ μ ᶜ Ѥ, ᶠ ⓤ Ꮯ Ж , 𝒦 ⒞ ᵘ F, Ｆ @ C ⓚ , Ѥ ᴄ u F, ⒡ ᵾ Ｃ k, ƒ μ ᶜ ᴋ, F 𝒰 Ｃ 𝓀, f ᵘ ¢ ᵏ, ᆿ 00 𝒸 𝕶, ꜰ υ ȼ Ｋ, Ϝ 𝓊 ȼ К , 𝕱 oo ɕ ᴋ, ғ 𝒰 Ꮯ ᴋ, ꜰ n 𝒸 K, ꜰ μ Ϛ К , F ∞ ȼ 𝖐, ⒡ 𐌵 Ↄ Κ , ƒ 𝖚 ⒞ 𝒦, ᶠ U C Ꮶ, ᶠ υ Ↄ ƙ, 𝓕 𝓊 C 𝓀, Ϝ Ｕ 𝒸 Ѥ, Ϝ U Ↄ 𝓀, 𝒻 Ｕ ⒞ ᵏ, F @ Ｃ К , ғ ᴜ 𝖈 ᴋ, ⒡ Ｕ 𝒸 К , ɟ Ｕ * ᵏ, 𝖋 Ц c Κ , ғ U Ↄ 𝕶, ƒ ⒰ 𝒞 ᵏ, ғ 𝖚 * Ｋ, 𝖋 n 𝕮 ⓚ , ᶠ 00 С К , 𝖋 Ц 𝒞 k, ƙ c Ц ᶠ, 𝕱 ⒰ Ѥ 𝖈, ꜰ ǔ ᴄ ⒦ , Ｆ 𝒰 Ↄ 𝓀, 𝒦 𝖈 υ ꜰ, 𝖋 𝖚 * ᵏ, 𝖋 00 𝕮 Ж , Κ Ｃ 𝖚 𝖋, ᶠ Ｕ С K, ꜰ 𝖀 𝖈 Κ , ɟ Ｕ ᶜ ⓚ , 𝒻 ∞ ȼ ᴋ, ƒ U К ć, ƒ υ ȼ ᴋ, ⒡ ∞ Ж ɕ, 𝖋 ᵘ 𝖈 ᵏ, F U Ϛ ʞ, ⓕ 𐌵 𝕮 Ж , 𝕱 𝒰 𝓀 Ↄ, Ϝ n * K, 𝓕 oo c ⓚ , ƒ Ｕ ¢ ʞ, ƒ u Ｃ ʞ, K ¢ μ ⒡ , ɟ ⒰ Ｋ ɔ, Ｆ U c k, Ｆ Ц 𝖈 ⓚ , 𝒻 Ｕ ᴋ ɔ, 𝖋 𝖀 Ꮯ 𝒦, 𝒻 𐌵 𝖈 ⓚ , ⓕ 𝖚 Ｃ К , ɟ ᵾ * ⒦ , ᶠ ᵘ ⒞ ⒦ , ƒ ⒰ ᴄ ᵏ, ⒡ ⒰ С K, 𝓕 ⒰ * ᴋ, ᆿ ∞ ʞ ɕ, 𝒻 n * Ѥ, Ϝ μ ᴄ 𝒦, k ć ᵘ ƒ, 𝓕 ᵘ ɕ 𝖐, ɟ Ц Ꮶ ᴄ, 𝓕 ᵾ ⒞ ᵏ, ғ ᵘ 𝒸 ᵏ, 𝖋 ᵾ * Ѥ, F 𝖚 Ꮯ Ｋ, ғ ⓤ 𝕮 ᴋ, ƒ u ɕ 𝖐, ƙ c ⒰ F, 𝒻 𝒰 ⓒ Κ , K ᶜ Ц 𝕱, ɟ 𝖚 c ⒦ , ƒ @ c Κ , Ϝ Ц ȼ Ḱ, ⒡ ᵘ 𝒞 ⒦ , ɟ ᵾ Ѥ ¢, Ｆ 𝖀 Ↄ 𝒦, Ϝ ᴜ 𝖐 𝖈, Ϝ 𝖀 ⒞ 𝖐, 𝕱 U Ꮯ ʞ, ƒ υ Ꮯ ᵏ, F ᵾ Ꮯ Κ , Ϝ ᵘ ⓒ ʞ, 𝓕 ⓤ ᶜ ƙ, ᆿ 𝒰 ⒞ 𝕶, f 𝖀 Ↄ Ѥ, 𝖋 Ｕ 𝒞 K, Ϝ ᴜ * 𝓀, ꜰ @ ⓒ ʞ, ƒ u ⓒ 𝒦, f Ｕ ⒞ k, 𝕱 00 ᴄ Ѥ, 𝒻 υ С K, F ᴜ ᴄ 𝕶, ⓕ oo Ↄ ⓚ , ⒡ ᵘ ɕ 𝓀, ⓕ υ ᴄ Κ , ᆿ Ｕ Ꮯ 𝕶, 𝒻 𝖀 Ꮯ Ꮶ, 𝖋 𐌵 Ć 𝓀, 𝓕 Ц ɕ К , f @ Ↄ ⓚ , ᴋ ᶜ U ꜰ, 𝓕 ᴜ c ⒦ , F ᵘ C 𝒦, 𝒻 00 𝖈 Ꮶ, ꜰ 00 𝖈 К , Ϝ 𝖚 Ϛ ᵏ, Ｆ 𐌵 c Ѥ, ⓕ oo Ↄ K, f ᵾ С ᵏ, ⓕ Ц c 𝒦, 𝓕 𐌵 c Ж , ⓕ 𝓊 𝒞 ƙ, ⓚ C n ғ, ɟ U ȼ 𝕶, 𝒻 00 K ȼ, 𝒻 𐌵 ᴄ 𝖐, 𝒻 Ц Ｃ 𝓀, 𝖋 Ц ¢ 𝓀, Ϝ ᵘ c k, ⒡ 𐌵 ¢ k, ƒ ⓤ ⓚ Ↄ, 𝒻 𐌵 𝕮 k, ƒ U Ↄ K, 𝓕 𝖀 ᴄ Ꮶ, ᆿ ⓤ 𝕮 ⒦ , Ж ɔ U 𝖋, ƒ υ * ᴋ, ƒ 𝓊 𝒞 k, 𝓕 U С ⒦ , 𝒻 𝖚 C Ж , ƒ μ Ꮯ ƙ, ⓕ n ᴄ ⒦ , ⓕ μ ⓒ Ж , ⒡ 00 ɕ 𝖐, 𝕱 ᴜ ᶜ 𝒦, ᆿ Ù Ж 𝖈, ⒦ ȼ Ｕ 𝖋, k C ⓤ ᆿ, Ϝ n ȼ ᵏ, ᴋ ȼ ᵾ ɟ, F 𝖀 ȼ Ѥ, ғ ⒰ ȼ 𝒦, f Ｕ Ж ⒞ , Ｆ ῠ 𝒸 ᵏ, Ｆ u 𝒸 Κ , Ｆ 00 ȼ 𝕶, ꜰ μ Ϛ Ꮶ, ᆿ 𝖀 𝒞 Ｋ, ⒡ n Ↄ Ж , F @ 𝒞 ƙ, ᶠ ὺ 𝒸 К , 𝒻 Ｕ Ｃ ᵏ, F U 𝖈 ⒦ , 𝒻 00 Ↄ 𝕶, ᶠ 𝖚 c К , ғ ⓤ 𝒞 𝒦, 𝓕 ⓤ 𝖈 Κ , 𝒻 Ｕ 𝒸 Ж , ⒡ 𝖀 ɔ Ꮶ, ⓚ ɔ 𝓊 f, 𝒻 U Ｃ K, F @ Ｃ Ѥ, ғ ᴜ С k, ɟ u * ƙ, ⓕ ᵾ ɕ 𝒦, 𝕱 00 ȼ Ｋ, 𝒻 υ 𝓀 𝖈, ƒ ⒰ * ʞ, ⓕ U Ↄ Ж , ꜰ U ȼ ƙ, ⒡ u С ⒦ , ꜰ ᴜ 𝕮 Ќ, ᆿ μ 𝒞 ⒦ , ⓕ @ ᴄ К , ᶠ υ ɔ ᵏ, ƙ Ↄ oo ꜰ, F ᴜ 𝕮 𝒦, 𝓕 ⒰ C ᵏ, 𝖋 Ｕ 𝒸 ƙ, ƒ ∞ C Ꮶ, 𝒻 ⒰ * Ｋ, 𝒻 u Ↄ ᴋ, ᆿ Ｕ ⓒ 𝓀, ᆿ U Ꮶ 𝕮, 𝓕 n 𝒦 𝖈, ƒ Ц C ƙ, ⒦ 𝖈 𝒰 ꜰ, Ｋ ¢ ᵘ f, 𝕱 ⒰ 𝖈 Ꮶ, 𝓀 ᴄ 00 𝖋, Ϝ Ｕ 𝒞 k, 𝕱 u ¢ ⒦ , 𝕱 𝓊 * Ѥ, ƒ 𝖀 С ᴋ, 𝒻 𝖀 Ｃ Ꮶ, 𝖋 @ 𝕮 Κ , ʞ С 𝖀 ᶠ, 𝖋 ᵾ Ϛ Ꮶ, ᶠ ⒰ ɔ 𝒦, F Ц ⒞ ʞ, ⒡ ⒰ К ɔ, ɟ υ ¢ 𝕶, Ѥ ȼ Ｕ ᆿ, 𝒻 ᴜ Ↄ ʞ, ғ 𝓊 * Ｋ, 𝒻 𝒰 ᴄ ʞ, F 𝖀 𝖈 ʞ, 𝒻 @ ȼ 𝒦, 𝒻 ⒰ * 𝖐, 𝒻 ᵾ ȼ 𝒦, Ｆ 𐌵 ¢ Ѥ, ꜰ ⓤ ƙ Ϛ, ⓕ 00 c ʞ, 𝕱 00 Ϛ K, 𝖋 υ Ↄ Κ , ꜰ μ ⓒ Ж , 𝒻 ᵘ Ϛ ʞ, Ϝ ᵘ Ↄ ᵏ, ⒡ ᵾ Ꮯ 𝒦, Ϝ ⒰ ȼ Ѥ, ƒ n 𝒞 Ѥ, ᆿ μ ⓒ k, 𝖋 Ц ɕ Κ , ғ μ 𝕮 Ѥ, f ⓤ Ꮯ 𝖐, ᵏ 𝕮 μ ƒ, ᵏ С 𝖚 𝓕, ᆿ ∞ 𝖈 𝒦, ғ ᵘ Ꮯ 𝓀, ƒ μ Ↄ k, f oo K ȼ, ɟ 𝓊 𝕶 С , ꜰ n 𝖈 K, 𝒻 00 𝖈 ᵏ, ᶠ μ ⓒ 𝓀, 𝖐 c ∞ Ϝ, ᆿ Ц Ć ⒦ , 𝕱 ᵘ ᴄ 𝒦, F 00 𝕮 ⓚ , ᶠ @ ȼ К , ...

And that’s not all: there are at least a bazingatillion more where those came from. Do you see now why this fundamentally cannot be done?

Full Disclosure

Because I don't believe in security through obscurity, here's the program that generates all those:

#!/usr/bin/env perl## unifuck - print infinite permutations of fuck in unicode aliases## Tom Christiansen <tchrist@perl.com># Mon May 23 09:37:27 MDT 2011use strict;use warnings;use charnames ":full";use Unicode::Normalize;binmode(STDOUT, ":utf8");our(@diddle, @fuck, %fuck); # initted down belowwhile (my($f,$u,$c,$k) = splice(@fuck, 0, 4)) {    $fuck{F}{$f}++;    $fuck{U}{$u}++;    $fuck{C}{$c}++;    $fuck{K}{$k}++;} my @F = keys %{ $fuck{F} };my @U = keys %{ $fuck{U} };my @C = keys %{ $fuck{C} };my @K = keys %{ $fuck{K} };while (1) {     my $f = $F[rand @F];    my $u = $U[rand @U];    my $c = $C[rand @C];    my $k = $K[rand @K];    for ($f,$u,$c,$k) {          next if length > 1;        next if /\p{EA=W}/;        next if /\pM/;        next if /\p{InEnclosedAlphanumerics}/;        s/$/$diddle[rand @diddle]/          if rand(100) < 15;        s/$/\N{COMBINING ENCLOSING KEYCAP}/ if rand(100) <  1;    }    if    (             0) {                                       }    elsif (rand(100) <  5) {     $u        = q(@)                  }     elsif (rand(100) <  5) {        $c     = q(*)                  }     elsif (rand(100) < 10) {       ($c,$k) = ($k,$c)               }     elsif (rand(100) < 15) { ($f,$u,$c,$k) = reverse ($f,$u,$c,$k) }    print NFC("$f $u $c $k\n");}BEGIN {    # ok to have repeats in each position, since they'll be counted only once    # per unique strings    @fuck = (        "\N{LATIN CAPITAL LETTER F}",        "\N{LATIN CAPITAL LETTER U}",        "\N{LATIN CAPITAL LETTER C}",        "\N{LATIN CAPITAL LETTER K}",        "\N{LATIN SMALL LETTER F}",        "\N{LATIN SMALL LETTER U}",        "\N{LATIN SMALL LETTER C}",        "\N{LATIN SMALL LETTER K}",        "\N{LATIN SMALL LETTER F}",        "\N{INFINITY}",        "\N{LATIN SMALL LETTER C}",        "\N{LATIN SMALL LETTER K}",        "\N{LATIN SMALL LETTER F}",        "\N{LATIN SMALL LETTER O}\N{LATIN SMALL LETTER O}",        "\N{LATIN SMALL LETTER C}",        "\N{KELVIN SIGN}",        "\N{LATIN SMALL LETTER F}",        "\N{DIGIT ZERO}\N{DIGIT ZERO}",        "\N{CENT SIGN}",        "\N{LATIN CAPITAL LETTER K}",        "\N{LATIN LETTER SMALL CAPITAL F}",        "\N{LATIN LETTER SMALL CAPITAL U}",        "\N{LATIN LETTER SMALL CAPITAL C}",        "\N{LATIN LETTER SMALL CAPITAL K}",        "\N{MODIFIER LETTER SMALL F}",        "\N{MODIFIER LETTER SMALL U}",        "\N{MODIFIER LETTER SMALL C}",        "\N{MODIFIER LETTER SMALL K}",        "\N{MATHEMATICAL SCRIPT SMALL F}",        "\N{MATHEMATICAL SCRIPT SMALL U}",        "\N{MATHEMATICAL SCRIPT SMALL C}",        "\N{MATHEMATICAL SCRIPT SMALL K}",        "\N{MATHEMATICAL BOLD FRAKTUR CAPITAL F}",        "\N{MATHEMATICAL BOLD FRAKTUR CAPITAL U}",        "\N{MATHEMATICAL BOLD FRAKTUR CAPITAL C}",        "\N{MATHEMATICAL BOLD FRAKTUR CAPITAL K}",        "\N{MATHEMATICAL BOLD FRAKTUR SMALL F}",        "\N{MATHEMATICAL BOLD FRAKTUR SMALL U}",        "\N{MATHEMATICAL BOLD FRAKTUR SMALL C}",        "\N{MATHEMATICAL BOLD FRAKTUR SMALL K}",        "\N{MATHEMATICAL BOLD SCRIPT CAPITAL F}",        "\N{MATHEMATICAL SCRIPT CAPITAL U}",        "\N{MATHEMATICAL SCRIPT CAPITAL C}",        "\N{MATHEMATICAL SCRIPT CAPITAL K}",        "\N{CIRCLED LATIN SMALL LETTER F}",        "\N{CIRCLED LATIN SMALL LETTER U}",        "\N{CIRCLED LATIN SMALL LETTER C}",        "\N{CIRCLED LATIN SMALL LETTER K}",        "\N{PARENTHESIZED LATIN SMALL LETTER F}",        "\N{PARENTHESIZED LATIN SMALL LETTER U}",        "\N{PARENTHESIZED LATIN SMALL LETTER C}",        "\N{PARENTHESIZED LATIN SMALL LETTER K}",        "\N{GREEK CAPITAL LETTER GAMMA}\N{COMBINING SHORT STROKE OVERLAY}",        "\N{GOTHIC LETTER QAIRTHRA}",        "\N{CHEROKEE LETTER TLI}",        "\N{CHEROKEE LETTER TSO}",        "\N{LATIN SMALL LETTER F WITH HOOK}",        "\N{GREEK SMALL LETTER MU}",        "\N{LATIN SMALL LETTER C WITH CURL}",        "\N{CYRILLIC CAPITAL LETTER IOTIFIED E}",        "\N{CYRILLIC CAPITAL LETTER GHE}\N{COMBINING SHORT STROKE OVERLAY}",        "\N{CYRILLIC CAPITAL LETTER TSE}",        "\N{CYRILLIC CAPITAL LETTER ES}",        "\N{CYRILLIC CAPITAL LETTER KA}",        "\N{CYRILLIC SMALL LETTER GHE WITH STROKE}",        "\N{LATIN SMALL CAPITAL LETTER U WITH STROKE}",        "\N{LATIN SMALL LETTER C WITH STROKE}",        "\N{LATIN SMALL LETTER K WITH HOOK}",        "\N{GREEK LETTER DIGAMMA}",        "\N{GREEK SMALL LETTER UPSILON}",        "\N{GREEK LETTER STIGMA}",        "\N{GREEK CAPITAL LETTER KAPPA}",        "\N{HANGUL JONGSEONG KHIEUKH}",        "\N{LATIN CAPITAL LETTER U}",        "\N{ROMAN NUMERAL REVERSED ONE HUNDRED}",        "\N{CYRILLIC CAPITAL LETTER ZHE}",        "\N{LATIN SMALL LETTER DOTLESS J WITH STROKE}",        "\N{LATIN SMALL LETTER N}",        "\N{LATIN SMALL LETTER OPEN O}",        "\N{LATIN SMALL LETTER TURNED K}",        "\N{FULLWIDTH LATIN CAPITAL LETTER F}",        "\N{FULLWIDTH LATIN CAPITAL LETTER U}",        "\N{FULLWIDTH LATIN CAPITAL LETTER C}",        "\N{FULLWIDTH LATIN CAPITAL LETTER K}",    );    @diddle = (        "\N{COMBINING GRAVE ACCENT}",        "\N{COMBINING ACUTE ACCENT}",        "\N{COMBINING CIRCUMFLEX ACCENT}",        "\N{COMBINING TILDE}",        "\N{COMBINING BREVE}",        "\N{COMBINING DOT ABOVE}",        "\N{COMBINING DIAERESIS}",        "\N{COMBINING CARON}",        "\N{COMBINING CANDRABINDU}",        "\N{COMBINING INVERTED BREVE}",        "\N{COMBINING GRAVE TONE MARK}",        "\N{COMBINING ACUTE TONE MARK}",        "\N{COMBINING GREEK PERISPOMENI}",        "\N{COMBINING FERMATA}",        "\N{COMBINING SUSPENSION MARK}",    );}

\b checks for a word boundary. According to http://www.regular-expressions.info/wordboundaries.html:

There are three different positions that qualify as word boundaries:

• Before the first character in the string, if the first character is a word character.
• After the last character in the string, if the last character is a word character.
• Between two characters in the string, where one is a word character and the other is not a word character.

"Word characters" are letters, digits, and underscores, so in the string "a$$", the word boundary occurs after the "a", not after the second "$".

You will probably need to explicitly specify the characters you consider to be "word boundaries" by using a class (e.g., [- '"]).

Now, when you said that it doesn't work at the end of the word I see the problem. $@ or any other such special characters aren't part of the word (so \b breaks the word after 'a' in case of 'a$$' if it isn't followed by any other letters in the input string). I suggest using [^a-z] to mark the end of the word to fix it.

preg_match_all("/\b".$f."(?:ing|er|es|s)?[^a-z]/si",$t,$m,PREG_SET_ORDER);