Matching Fasta file header and section of sequence, printing each header only once

Question

I have a Fasta file which I am opening and reading. I need to search for certain regions of the DNA sequence and, for each match found, print the sequence header followed by all matches within that sequence. The problem is that I don't want to print the same header multiple times, and I want to print it above the matched sections.

If I use the following code, I get the desired output but the matched regions of DNA are printed above their corresponding header. I cannot flip the two blocks of code because that cuts off the first results:

# First, I open my file and print a warning if it fails.
unless (open FILE, "<", '/scratch/SampleDataFiles/test.fasta') {
    die "Sorry", $!;
    }

$/ = ">";        #This changes the record separator from \n to >, so I can chomp it later.

    my @file = <FILE>;
    my $file = "@file";
    chomp $file;
    #To view the file I can--
    #print $file;


   my $count = 0;    #here I will count the matched regions

    my $sequence_count = 0;   #here I will count the sequences
                               #that contain a matched region

    foreach $file (@file) {

            #I look for each header and its following sequence
            #And count the total sequences in the file
            if ($file =~ /(.*;.*;?\n)(\w+)/) {
                    my $head = $1;
                    my $sequence = $2;
                    $sequence_count = $sequence_count +1;


                    #Now, I use the sequences I matched and search for a
                    #hydrophobic region

                    while ($sequence =~ /([VILMFWCA]{8,}?)/gi) {

                            #I want to know what the position of the match is
                            my $pos = pos($sequence)-7;


                            print "\n", $1, " found at ", $pos;
                    }

                            #I use the count variable I made earlier to count up each
                            #time I match a sequence that has one or more hydrophobic region

                    if ($sequence =~ /([VILMFWCA]{8,}?)/gi) {
                                    print "\n", "Hydrophobic region(s) found in ", $head, "\n", "-------------------------------------", "\n";
                                    $count = $count +1;
                    }


            }
    }


print "Hydrophobic region(s) found in ", $count, " out of ", $sequence_count , " sequences.", "\n", "\n";

This is the output:

AVVAAVMW found at 325
Hydrophobic region(s) found in P30450 | Homo sapiens (Human). | 
NCBI_TaxID=9606; | 365 |    Name=HLA-A; Synonyms=HLAA;

-------------------------------------

VAVLMLCL found at 170
LLALVAIF found at 493
IWICWFAA found at 705
LALALAFA found at 970
Hydrophobic region(s) found in A7MBM2 | Homo sapiens (Human). | 
NCBI_TaxID=9606; | 1401 |    Name=DISP2; Synonyms=DISPB, KIAA1742;

-------------------------------------
Hydrophobic region(s) found in 2 out of 15 sequences.

This is the output I get if I switch them:

Hydrophobic region(s) found in P30450 | Homo sapiens (Human). | 
NCBI_TaxID=9606; | 365 |    Name=HLA-A; Synonyms=HLAA;

-------------------------------------

Hydrophobic region(s) found in A7MBM2 | Homo sapiens (Human). | 
NCBI_TaxID=9606; | 1401 |    Name=DISP2; Synonyms=DISPB, KIAA1742;


LLALVAIF found at 493
IWICWFAA found at 705
LALALAFA found at 970

Hydrophobic region(s) found in 2 out of 15 sequences.` 

Per my teacher's recommendation, I have adjusted my code as follows so that I include everything within the larger while loop and restrict the number of prints with a counter. This new code prints each new header one time, and below it prints each instance of a found region of DNA (essentially flipping what I had before).

my $temp_count = 0;
my $count = 0;
if ($file =~ /(.*;.*;?\n)(\w+)/) {
                    my $head = $1;
                    my $sequence = $2;
                    $sequence_count = $sequence_count +1;

                    #Now I use the sequences that I found, and
                    #search them for a hydrophobic region
                    while ($sequence =~ /([VILMFWCA]{8,}?)/gi) {

                                    #I use the count variables I made earlier
                                    #I count all times I match a sequence that has one or more hydrophobic region
                                    $temp_count = $temp_count +1;

                                    #But I don't want the header repeated for the same sequence, so I limit the
                                    #times that it can print
                                    if ($temp_count <= 2) {
                                            print "\n", "Hydrophobic region(s) found in ", $head, "\n";
                                            $count = $count +1;
                                    }

                                    #I want to know what the position of the match is
                                    #within the sequence
                                    my $pos = pos($sequence)-7;
                                    print $1, " found at ", $pos, "\n", "\n";

                   }


           }


    }

print "\n", "\n", "-------------------------", "\n", "Hydrophobic region(s) found in ", $count, " out of ", $sequence_count , " sequences.", "\n", "\n";

If you are interested, the Fasta file looks something like this:

>P31946 | Homo sapiens (Human). | NCBI_TaxID=9606; | 246 |    Name=YWHAB;
MTMDKSELVQKAKLAEQAERYDDMAAAMKAVTEQGHELSNEERNLLSVAYKNVVGARRSSWRVISSIEQKTERNEKKQQMGKEYREKIEAELQDICNDVLELLDKYLIPNATQPESKVFYLKMKGDYFRYLSEVASGDNKQTTVSNSQQAYQEAFEISKKEMQPTHPIRL
GLALNFSVFYYEILNSPEKACSLAKTAFDEAIAELDTLNEESYKDSTLIMQLLRDNLTLWTSENQGDEGDAGEGEN
>P62258 | Homo sapiens (Human). | NCBI_TaxID=9606; | 255 |    Name=YWHAE;
MDDREDLVYQAKLAEQAERYDEMVESMKKVAGMDVELTVEERNLLSVAYKNVIGARRASWRIISSIEQKEENKGGEDKLKMIREYRQMVETELKLICCDILDVLDKHLIPAANTGESKVFYYKMKGDYHRYLAEFATGNDRKEAAENSLVAYKAASDIAMTELPPTHPIR
LGLALNFSVFYYEILNSPDRACRLAKAAFDDAIAELDTLSEESYKDSTLIMQLLRDNLTLWTSDMQGDGEEQNKEALQDVEDENQ
>Q04917 | Homo sapiens (Human). | NCBI_TaxID=9606; | 246 |    Name=YWHAH; Synonyms=YWHA1;
MGDREQLLQRARLAEQAERYDDMASAMKAVTELNEPLSNEDRNLLSVAYKNVVGARRSSWRVISSIEQKTMADGNEKKLEKVKAYREKIEKELETVCNDVLSLLDKFLIKNCNDFQYESKVFYLKMKGDYYRYLAEVASGEKKNSVVEASEAAYKEAFEISKEQMQPTHP
IRLGLALNFSVFYYEIQNAPEQACLLAKQAFDDAIAELDTLNEDSYKDSTLIMQLLRDNLTLWTSDQQDEEAGEGN
>P30450 | Homo sapiens (Human). | NCBI_TaxID=9606; | 365 |    Name=HLA-A; Synonyms=HLAA;
MAVMAPRTLVLLLSGALALTQTWAGSHSMRYFYTSVSRPGRGEPRFIAVGYVDDTQFVRFDSDAASQRMEPRAPWIEQEGPEYWDRNTRNVKAHSQTDRANLGTLRGYYNQSEDGSHTIQRMYGCDVGPDGRFLRGYQQDAYDGKDYIALNEDLRSWTAADMAAQITQRK
WETAHEAEQWRAYLEGRCVEWLRRYLENGKETLQRTDAPKTHMTHHAVSDHEATLRCWALSFYPAEITLTWQRDGEDQTQDTELVETRPAGDGTFQKWASVVVPSGQEQRYTCHVQHEGLPKPLTLRWEPSSQPTIPIVGIIAGLVLFGAVIAGAVVAAVMWRRKSSDRK
GGSYSQAASSDSAQGSDMSLTACKV
>Q156A1 | Homo sapiens (Human). | NCBI_TaxID=9606; | 80 |    Name=ATXN8;
MQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQQ
>Q9UQB9 | Homo sapiens (Human). | NCBI_TaxID=9606; | 309 |    Name=AURKC; Synonyms=AIE2, AIK3, ARK3, STK13;
MSSPRAVVQLGKAQPAGEELATANQTAQQPSSPAMRRLTVDDFEIGRPLGKGKFGNVYLARLKESHFIVALKVLFKSQIEKEGLEHQLRREIEIQAHLQHPNILRLYNYFHDARRVYLILEYAPRGELYKELQKSEKLDEQRTATIIEELADALTYCHDKKVIHRDIKPE
NLLLGFRGEVKIADFGWSVHTPSLRRKTMCGTLDYLPPEMIEGRTYDEKVDLWCIGVLCYELLVGYPPFESASHSETYRRILKVDVRFPLSMPLGARDLISRLLRYQPLERLPLAQILKHPWVQAHSRRVLPPCAQMAS
>O75366 | Homo sapiens (Human). | NCBI_TaxID=9606; | 819 |    Name=AVIL;
MPLTSAFRAVDNDPGIIVWRIEKMELALVPVSAHGNFYEGDCYVILSTRRVASLLSQDIHFWIGKDSSQDEQSCAAIYTTQLDDYLGGSPVQHREVQYHESDTFRGYFKQGIIYKQGGVASGMKHVETNTYDVKRLLHVKGKRNIRATEVEMSWDSFNRGDVFLLDLGKV
IIQWNGPESNSGERLKAMLLAKDIRDRERGGRAEIGVIEGDKEAASPELMKVLQDTLGRRSIIKPTVPDEIIDQKQKSTIMLYHISDSAGQLAVTEVATRPLVQDLLNHDDCYILDQSGTKIYVWKGKGATKAEKQAAMSKALGFIKMKSYPSSTNVETVNDGAESAMFK
QLFQKWSVKDQTMGLGKTFSIGKIAKVFQDKFDVTLLHTKPEVAAQERMVDDGNGKVEVWRIENLELVPVEYQWYGFFYGGDCYLVLYTYEVNGKPHHILYIWQGRHASQDELAASAYQAVEVDRQFDGAAVQVRVRMGTEPRHFMAIFKGKLVIFEGGTSRKGNAEPDP
PVRLFQIHGNDKSNTKAVEVPAFASSLNSNDVFLLRTQAEHYLWYGKGSSGDERAMAKELASLLCDGSENTVAEGQEPAEFWDLLGGKTPYANDKRLQQEILDVQSRLFECSNKTGQFVVTEITDFTQDDLNPTDVMLLDTWDQVFLWIGAEANATEKESALATAQQYLH
THPSGRDPDTPILIIKQGFEPPIFTGWFLAWDPNIWSAGKTYEQLKEELGDAAAIMRITADMKNATLSLNSNDSEPKYYPIAVLLKNQNQELPEDVNPAKKENYLSEQDFVSVFGITRGQFAALPGWKQLQMKKEKGLF
>Q9UPA5 | Homo sapiens (Human). | NCBI_TaxID=9606; | 3926 |    Name=BSN; Synonyms=KIAA0434, ZNF231;
MGNEVSLEGGAGDGPLPPGGAGPGPGPGPGPGAGKPPSAPAGGGQLPAAGAARSTAVPPVPGPGPGPGPGPGPGSTSRRLDPKEPLGNQRAASPTPKQASATTPGHESPRETRAQGPAGQEADGPRRTLQVDSRTQRSGRSPSVSPDRGSTPTSPYSVPQIAPLPSSTLC
PICKTSDLTSTPSQPNFNTCTQCHNKVCNQCGFNPNPHLTQVKEWLCLNCQMQRALGMDMTTAPRSKSQQQLHSPALSPAHSPAKQPLGKPDQERSRGPGGPQPGSRQAETARATSVPGPAQAAAPPEVGRVSPQPPQPTKPSTAEPRPPAGEAPAKSATAVPAGLGATE
QTQEGLTGKLFGLGASLLTQASTLMSVQPEADTQGQPAPSKGTPKIVFNDASKEAGPKPLGSGPGPGPAPGAKTEPGARMGPGSGPGALPKTGGTTSPKHGRAEHQAASKAAAKPKTMPKERAICPLCQAELNVGSKSPANYNTCTTCRLQVCNLCGFNPTPHLVEKTEW
LCLNCQTKRLLEGSLGEPTPLPPPTSQQPPVGAPHRASGTSPLKQKGPQGLGQPSGPLPAKASPLSTKASPLPSKASPQAKPLRASEPSKTPSSVQEKKTRVPTKAEPMPKPPPETTPTPATPKVKSGVRRAEPATPVVKAVPEAPKGGEAEDLVGKPYSQDASRSPQSL
SDTGYSSDGISSSQSEITGVVQQEVEQLDSAGVTGPHPPSPSEIHKVGSSMRPLLQAQGLAPSERSKPLSSGTGEEQKQRPHSLSITPEAFDSDEELEDILEEDEDSAEWRRRREQQDTAESSDDFGSQLRHDYVEDSSEGGLSPLPPQPPARAAELTDEDFMRRQILEM
SAEEDNLEEDDTATSGRGLAKHGTQKGGPRPRPEPSQEPAALPKRRLPHNATTGYEELLPEGGSAEATDGSGTLQGGLRRFKTIELNSTGSYGHELDLGQGPDPSLDREPELEMESLTGSPEDRSRGEHSSTLPASTPSYTSGTSPTSLSSLEEDSDSSPSRRQRLEEAK
QQRKARHRSHGPLLPTIEDSSEEEELREEEELLREQEKMREVEQQRIRSTARKTRRDKEELRAQRRRERSKTPPSNLSPIEDASPTEELRQAAEMEELHRSSCSEYSPSPSLDSEAEALDGGPSRLYKSGSEYNLPTFMSLYSPTETPSGSSTTPSSGRPLKSAEEAYEE
MMRKAELLQRQQGQAAGARGPHGGPSQPTGPRGLGSFEYQDTTDREYGQAAQPAAEGTPASLGAAVYEEILQTSQSIVRMRQASSRDLAFAEDKKKEKQFLNAESAYMDPMKQNGGPLTPGTSPTQLAAPVSFSTPTSSDSSGGRVIPDVRVTQHFAKETQDPLKLHSSP
ASPSSASKEIGMPFSQGPGTPATTAVAPCPAGLPRGYMTPASPAGSERSPSPSSTAHSYGHSPTTANYGSQTEDLPQAPSGLAAAGRAAREKPLSASDGEGGTPQPSRAYSYFASSSPPLSPSSPSESPTFSPGKMGPRATAEFSTQTPSPAPASDMPRSPGAPTPSPMV
AQGTQTPHRPSTPRLVWQESSQEAPFMVITLASDASSQTRMVHASASTSPLCSPTETQPTTHGYSQTTPPSVSQLPPEPPGPPGFPRVPSAGADGPLALYGWGALPAENISLCRISSVPGTSRVEPGPRTPGTAVVDLRTAVKPTPIILTDQGMDLTSLAVEARKYGLAL
DPIPGRQSTAVQPLVINLNAQEHTFLATATTVSITMASSVFMAQQKQPVVYGDPYQSRLDFGQGGGSPVCLAQVKQVEQAVQTAPYRSGPRGRPREAKFARYNLPNQVAPLARRDVLITQMGTAQSIGLKPGPVPEPGAEPHRATPAELRSHALPGARKPHTVVVQMGEG
TAGTVTTLLPEEPAGALDLTGMRPESQLACCDMVYKLPFGSSCTGTFHPAPSVPEKSMADAAPPGQSSSPFYGPRDPEPPEPPTYRAQGVVGPGPHEEQRPYPQGLPGRLYSSMSDTNLAEAGLNYHAQRIGQLFQGPGRDSAMDLSSLKHSYSLGFADGRYLGQGLQYG
SVTDLRHPTDLLAHPLPMRRYSSVSNIYSDHRYGPRGDAVGFQEASLAQYSATTAREISRMCAALNSMDQYGGRHGSGGGGPDLVQYQPQHGPGLSAPQSLVPLRPGLLGNPTFPEGHPSPGNLAQYGPAAGQGTAVRQLLPSTATVRAADGMIYSTINTPIAATLPITT
QPASVLRPMVRGGMYRPYASGGITAVPLTSLTRVPMIAPRVPLGPTGLYRYPAPSRFPIASSVPPAEGPVYLGKPAAAKAPGAGGPSRPEMPVGAAREEPLPTTTPAAIKEAAGAPAPAPLAGQKPPADAAPGGGSGALSRPGFEKEEASQEERQRKQQEQLLQLERERV
ELEKLRQLRLQEELERERVELQRHREEEQLLVQRELQELQTIKHHVLQQQQEERQAQFALQREQLAQQRLQLEQIQQLQQQLQQQLEEQKQRQKAPFPAACEAPGRGPPLAAAELAQNGQYWPPLTHAAFIAMAGPEGLGQPREPVLHRGLPSSASDMSLQTEEQWEASR
SGIKKRHSMPRLRDACELESGTEPCVVRRIADSSVQTDDEDGESRYLLSRRRRARRSADCSVQTDDEDSAEWEQPVRRRRSRLPRHSDSGSDSKHDATASSSSAAATVRAMSSVGIQTISDCSVQTEPDQLPRVSPAIHITAATDPKVEIVRYISAPEKTGRGESLACQT
EPDGQAQGVAGPQLVGPTAISPYLPGIQIVTPGPLGRFEKKKPDPLEIGYQAHLPPESLSQLVSRQPPKSPQVLYSPVSPLSPHRLLDTSFASSERLNKAHVSPQKHFTADSALRQQTLPRPMKTLQRSLSDPKPLSPTAEESAKERFSLYQHQGGLGSQVSALPPNSLV
RKVKRTLPSPPPEEAHLPLAGQASPQLYAASLLQRGLTGPTTVPATKASLLRELDRDLRLVEHESTKLRKKQAELDEEEKEIDAKLKYLELGITQRKESLAKDRGGRDYPPLRGLGEHRDYLSDSELNQLRLQGCTTPAGQFVDFPATAAAPATPSGPTAFQQPRFQPPA
PQYSAGSGGPTQNGFPAHQAPTYPGPSTYPAPAFPPGASYPAEPGLPNQQAFRPTGHYAGQTPMPTTQSTLFPVPADSRAPLQKPRQTSLADLEQKVPTNYEVIASPVVPMSSAPSETSYSGPAVSSGYEQGKVPEVPRAGDRGSVSQSPAPTYPSDSHYTSLEQNVPRN
YVMIDDISELTKDSTSTAPDSQRLEPLGPGSSGRPGKEPGEPGVLDGPTLPCCYARGEEESEEDSYDPRGKGGHLRSMESNGRPASTHYYGDSDYRHGARVEKYGPGPMGPKHPSKSLAPAAISSKRSKHRKQGMEQKISKFSPIEEAKDVESDLASYPPPAVSSSLVSR
GRKFQDEITYGLKKNVYEQQKYYGMSSRDAVEDDRIYGGSSRSRAPSAYSGEKLSSHDFSGWGKGYEREREAVERLQKAGPKPSSLSMAHSRVRPPMRSQASEEESPVSPLGRPRPAGGPLPPGGDTCPQFCSSHSMPDVQEHVKDGPRAHAYKREEGYILDDSHCVVSD
SEAYHLGQEETDWFDKPRDARSDRFRHHGGHAVSSSSQKRGPARHSYHDYDEPPEEGLWPHDEGGPGRHASAKEHRHGDHGRHSGRHTGEEPGRRAAKPHARDLGRHEARPHSQPSSAPAMPKKGQPGYPSSAEYSQPSRASSAYHHASDSKKGSRQAHSGPAALQSKAE
PQAQPQLQGRQAAPGPQQSQSPSSRQIPSGAASRQPQTQQQQQGLGLQPPQQALTQARLQQQSQPTTRGSAPAASQPAGKPQPGPSTATGPQPAGPPRAEQTNGSKGTAKAPQQGRAPQAQPAPGPGPAGVKAGARPGGTPGAPAGQPGADGESVFSKILPGGAAEQAGK
LTEAVSAFGKKFSSFW
>Q9NSI6 | Homo sapiens (Human). | NCBI_TaxID=9606; | 2320 |    Name=BRWD1; Synonyms=C21orf107, WDR9;
MAEPSSARRPVPLIESELYFLIARYLSAGPCRRAAQVLVQELEQYQLLPKRLDWEGNEHNRSYEELVLSNKHVAPDHLLQICQRIGPMLDKEIPPSISRVTSLLGAGRQSLLRTAKDCRHTVWKGSAFAALHRGRPPEMPVNYGSPPNLVEIHRGKQLTGCSTFSTAFPG
TMYQHIKMHRRILGHLSAVYCVAFDRTGHRIFTGSDDCLVKIWSTHNGRLLSTLRGHSAEISDMAVNYENTMIAAGSCDKIIRVWCLRTCAPVAVLQGHTGSITSLQFSPMAKGSQRYMVSTGADGTVCFWQWDLESLKFSPRPLKFTEKPRPGVQMLCSSFSVGGMFLA
TGSTDHVIRMYFLGFEAPEKIAELESHTDKVDSIQFCNNGDRFLSGSRDGTARIWRFEQLEWRSILLDMATRISGDLSSEEERFMKPKVTMIAWNQNDSIVVTAVNDHVLKVWNSYTGQLLHNLMGHADEVFVLETHPFDSRIMLSAGHDGSIFIWDITKGTKMKHYFNM
IEGQGHGAVFDCKFSQDGQHFACTDSHGHLLIFGFGCSKPYEKIPDQMFFHTDYRPLIRDSNNYVLDEQTQQAPHLMPPPFLVDVDGNPHPTKYQRLVPGRENSADEHLIPQLGYVATSDGEVIEQIISLQTNDNDERSPESSILDGMIRQLQQQQDQRMGADQDTIPRG
LSNGEETPRRGFRRLSLDIQSPPNIGLRRSGQVEGVRQMHQNAPRSQIATERDLQAWKRRVVVPEVPLGIFRKLEDFRLEKGEEERNLYIIGRKRKTLQLSHKSDSVVLVSQSRQRTCRRKYPNYGRRNRSWRELSSGNESSSSVRHETSCDQSEGSGSSEEDEWRSDRK
SESYSESSSDSSSRYSDWTADAGINLQPPLRTSCRRRITRFCSSSEDEISTENLSPPKRRRKRKKENKPKKENLRRMTPAELANMEHLYEFHPPVWITDTTLRKSPFVPQMGDEVIYFRQGHEAYIEAVRRNNIYELNPNKEPWRKMDLRDQELVKIVGIRYEVGPPTLC
CLKLAFIDPATGKLMDKSFSIRYHDMPDVIDFLVLRQFYDEARQRNWQSCDRFRSIIDDAWWFGTVLSQEPYQPQYPDSHFQCYIVRWDNTEIEKLSPWDMEPIPDNVDPPEELGASISVTTDELEKLLYKPQAGEWGQKSRDEECDRIISGIDQLLNLDIAAAFAGPVD
LCTYPKYCTVVAYPTDLYTIRMRLVNRFYRRLSALVWEVRYIEHNARTFNEPESVIARSAKKITDQLLKFIKNQHCTNISELSNTSENDEQNAEDLDDSDLPKTSSGRRRVHDGKKSIRATNYVESNWKKQCKELVNLIFQCEDSEPFRQPVDLVEYPDYRDIIDTPMDF
GTVRETLDAGNYDSPLEFCKDIRLIFSNAKAYTPNKRSKIYSMTLRLSALFEEKMKKISSDFKIGQKFNEKLRRSQRFKQRQNCKGDSQPNKSIRNLKPKRLKSQTKIIPELVGSPTQSTSSRTAYLGTHKTSAGISSGVTSGDSSDSAESSERRKRNRPITNGSTLSES
EVEDSLATSLSSSASSSSEESKESSRARESSSRSGLSRSSNLRVTRTRAAQRKTGPVSLANGCGRKATRKRVYLSDSDNNSLETGEILKARAGNNRKVLRKCAAVAANKIKLMSDVEENSSSESVCSGRKLPHRNASAVARKKLLHNSEDEQSLKSEIEEEELKDENQPL
PVSSSHTAQSNVDESENRDSESESDLRVARKNWHANGYKSHTPAPSKTKFLKIESSEEDSKSHDSDHACNRTAGPSTSVQKLKAESISEEADSEPGRSGGRKYNTFHKNASFFKKTKILSDSEDSESEEQDREDGKCHKMEMNPISGNLNCDPIAMSQCSSDHGCETDLD
SDDDKIEKPNNFMKDSASQDNGLSRKISRKRVCSSDSDSSLQVVKKSSKARTGLLRITRRCAATAANKIKLMSDVEDVSLENVHTRSKNGRKKPLHLACTTAKKKLSDCEGSVHCEVPSEQYACEGKPPDPDSEGSTKVLSQALNGDSDSEDMLNSEHKHRHTNIHKIDA
PSKRKSSSVTSSGEDSKSHIPGSETDRTFSSESTLAQKATAENNFEVELNYGLRRWNGRRLRTYGKAPFSKTKVIHDSQETAEKEVKRKRSHPELENVKISETTGNSKFRPDTSSKSSDLGSVTESDIDCTDNTKTKRRKTKGKAKVVRKEFVPRDREPNTKVRTCMHNQ
KDAVQMPSETLKAKMVPEKVPRRCATVAANKIKIMSNLKETISGPENVWIRKSSRKLPHRNASAAAKKKLLNVYKEDDTTINSESEKELEDINRKMLFLRGFRSWKENAQ
>Q96KE9 | Homo sapiens (Human). | NCBI_TaxID=9606; | 485 |    Name=BTBD6; Synonyms=BDPL;
MAAELYAPASAAAADLANSNAGAAVGRKAGPRSPPSAPAPAPPPPAPAPPTLGNNHQESPGWRCCRPTLRERNALMFNNELMADVHFVVGPPGATRTVPAHKYVLAVGSSVFYAMFYGDLAEVKSEIHIPDVEPAAFLILLKYMYSDEIDLEADTVLATLYAAKKYIVPALAKACVNFLETSLEAKNACVLLSQSRLFEEPELTQRCWEVIDAQAEMALRSEGFCEIDRQTLEIIVTREALNTKEAVVFEAVLNWAEAECKRQGLPITPRNKRHVLGRALYLVRIPTMTLEEFANGAAQSDILTLEETHSIFLWYTATNKPRLDFPLTKRKGLAPQRCHRFQSSAYRSNQWRYRGRCDSIQFAVDRRVFIAGLGLYGSSSGKAEYSVKIELKRLGVVLAQNLTKFMSDGSSNTFPVWFEHPVQVEQDTFYTASAVLDGSELSYFGQEGMTEVQCGKVAFQFQCSSDSTNGTGVQGGQIPELIFYA
>P0C7T9 | Homo sapiens (Human). | NCBI_TaxID=9606; | 278 |    Name=BZW1L1;
MENSERNKLAMLTGVLLANGTLNASILNSLYNENLVKEGVSAAFAVKLFKSWINEKDINAVAASLRKVSMDNRLMELFPANKQSVEHFTKYFTEAGLKELSEYVRNQQTIGARKELQKELQEQMSRGDPFKDIILYVKEEMKKNNIPEPVVIGIVWSSVMSTVEWNKKEELVAEQAIKHLKQYSPLLAAFTTQGQSELTLLLKIQEYCYDNIHFMKAFQKIVVLFYKAEVLSEEPILKWYKDAHVAKGKSVFLEQMKKFVEWLKNAEEESESEAEEGD
>Q8IYA2 | Homo sapiens (Human). | NCBI_TaxID=9606; | 1237 |    Name=CCDC144C;
MVSWGGEKRGGAEGSPKPAVYATRKTGSVRSQEDQWYLGYPGDQWSSGFSYSWWKNSVGSESKHGEGALDQPQHDVRLEDLGELHRAARSGDVPGVEHVLVPGDTGVDKRDRKKSIQQLVPEYKEKQTPESLPQNNNPDWHPTNLTLSDETCQRSKNLKVDDKCPSVSPSMPENQSATKELGQMNLTEREKMDTGVKTSQEPEMAKDCDREDIPIYPVLPHVQKSEEMRIEQGKLEWKNQLKLVINELKQRFGEIYEKYKIPACPEEEPLLDNSTRGTDVKDIPFNLTNNIPGCEEEDASEISVSVVFETFPEQKEPSLKNIIHSYYHPYSGSQEHVCQSSSKLHLHENKLDCDNDNKPGIGHIFSTDKNFHNDASTKKARNPEVVTVEMKEDQEFDLQMTKNMNQNSDSGSTNNYKSLKPKLENLSSLPPDSDRTSEVYLHEELQQDMQKFKNEVNTLEEEFLALKKENVQLHKEVEEEMEKHRSNSTELSGTLTDGTTVGNDDDGLNQQIPRKENGEHDRLALKQENEEKRNADMLYNKDSEQLRIKEEECGKVVETKQQLKWNLRRLVKELRTVVQERNDAQKQLSEEQDARILQDQILTSKQKELEMAQKKRNPEISHRHQKEKDLFHENCMLQEEIALLRLEIDTIKNQNKQKEKKYFEDIEVVKEKNDNLQKIIKRNEETLTETILQYSGQLNNLTAENKMLNSELENGKENQERLEIEMESYRCRLAAAVHDCDQSQTARDLKLDFQRTRQEWVRLHDKMKVDMSGLQAKNEILSEKLSNAESKINSLQIQLHNTRDALGRESLILERVQRDLSQTQCQKKETEQMYQSKLKKYIAKQESVEERLSQLQSENMLLRQQLDDVHKKANSQEKTISTIQDQFHSAAKNLQAESEKQILSLQEKNKELMDEYNHLKERMDQCEKEKAGRKIDLTEAQETVPSRCLHLDAENEVLQLQQTLFSMKAIQKQCETLQKNKKQLKQEVVNLKSYMERNMLERGEAEWHKLLIEERARKEIEEKLNEAILTLQKQAAVSHEQLAQLREDNTTSIKTQMELTVIDLESEISRIKTSQADFNKTKLERYKELYLEEVKVRESLSNELSRTNEMIAEVSTQLTVEKEQTRSRSLFTAYATRPVLESPCVGNLNDSEGLNRKHIPRKKRSALKDMESYLLKMQQKLQNDLTAEVAGSSQTGLHRIPQCSSFSSSSLHLLLCSICQPFFLILQLLLNMNLDPI
>A7MBM2 | Homo sapiens (Human). | NCBI_TaxID=9606; | 1401 |    Name=DISP2; Synonyms=DISPB, KIAA1742;
MDGDSSSSSGGSGPAPGPGPEGEQRPEGEPLAPDGGSPDSTQTKAVPPEASPERSCSLHSCPLEDPSSSSGPPPTTSTLQPVGPSSPLAPAHFTYPRALQEYQGGSSLPGLGDRAALCSHGSSLSPSPAPSQRDGTWKPPAVQHHVVSVRQERAFQMPKSYSQLIAEWPVAVLMLCLAVIFLCTLAGLLGARLPDFSKPLLGFEPRDTDIGSKLVVWRALQALTGPRKLLFLSPDLELNSSSSHNTLRPAPRGSAQESAVRPRRMVEPLEDRRQENFFCGPPEKSYAKLVFMSTSSGSLWNLHAIHSMCRMEQDQIRSHTSFGALCQRTAANQCCPSWSLGNYLAVLSNRSSCLDTTQADAARTLALLRTCALYYHSGALVPSCLGPGQNKSPRCAQVPTKCSQSSAIYQLLHFLLDRDFLSPQTTDYQVPSLKYSLLFLPTPKGASLMDIYLDRLATPWGLADNYTSVTGMDLGLKQELLRHFLVQDTVYPLLALVAIFFGMALYLRSLFLTLMVLLGVLGSLLVAFFLYQVAFRMAYFPFVNLAALLLLSSVCANHTLIFFDLWRLSKSQLPSGGLAQRVGRTMHHFGYLLLVSGLTTSAAFYASYLSRLPAVRCLALFMGTAVLVHLALTLVWLPASAVLHERYLARGCARRARGRWEGSAPRRLLLALHRRLRGLRRAAAGTSRLLFQRLLPCGVIKFRYIWICWFAALAAGGAYIAGVSPRLRLPTLPPPGGQVFRPSHPFERFDAEYRQLFLFEQLPQGEGGHMPVVLVWGVLPVDTGDPLDPRSNSSLVRDPAFSASGPEAQRWLLALCHRARNQSFFDTLQEGWPTLCFVETLQRWMESPSCARLGPDLCCGHSDFPWAPQFFLHCLKMMALEQGPDGTQDLGLRFDAHGSLAALVLQFQTNFRNSPDYNQTQLFYNEVSHWLAAELGMAPPGLRRGWFTSRLELYSLQHSLSTEPAVVLGLALALAFATLLLGTWNVPLSLFSVAAVAGTVLLTVGLLVLLEWQLNTAEALFLSASVGLSVDFTVNYCISYHLCPHPDRLSRVAFSLRQTSCATAVGAAALFAAGVLMLPATVLLYRKLGIILMMVKCVSCGFASFFFQSLCCFFGPEKNCGQILWPCAHLPWDAGTGDPGGEKAGRPRPGSVGGMPGSCSEQYELQPLARRRSPSFDTSTATSKLSHRPSVLSEDLQLHDGPCCSRPPPAPASPRELLLDHQAVFSQCPALQTSSPYKQAGPSPKTRARQDSQGEEAEPLPASPEAPAHSPKAKAADPPDGFCSSASTLEGLSVSDETCLSTSEPSARVPDSVGVSPDDLDDTGQPVLERGQLNGKRDTLWLALRETVYDPSLPASHHSSLSWKGRGGPGDGSPVVLPNSQPDLPDVWLRRPSTHTSGYSS
>Q96HU8 | Homo sapiens (Human). | NCBI_TaxID=9606; | 199 |    Name=DIRAS2;
MPEQSNDYRVAVFGAGGVGKSSLVLRFVKGTFRESYIPTVEDTYRQVISCDKSICTLQITDTTGSHQFPAMQRLSISKGHAFILVYSITSRQSLEELKPIYEQICEIKGDVESIPIMLVGNKCDESPSREVQSSEAEALARTWKCAFMETSAKLNHNVKELFQELLNLEKRRTVSLQIDGKKSKQQKRKEKLKGKCVIM
>Q8N4W6 | Homo sapiens (Human). | NCBI_TaxID=9606; | 341 |    Name=DNAJC22;
MAKGLLVTYALWAVGGPAGLHHLYLGRDSHALLWMLTLGGGGLGWLWEFWKLPSFVAQANRAQGQRQSPRGVTPPLSPIRFAAQVIVGIYFGLVALISLSSMVNFYIVALPLAVGLGVLLVAAVGNQTSDFKNTLGSAFLTSPIFYGRPIAILPISVAASITAQRHRRYKALVASEPLSVRLYRLGLAYLAFTGPLAYSALCNTAATLSYVAETFGSFLNWFSFFPLLGRLMEFVLLLPYRIWRLLMGETGFNSSCFQEWAKLYEFVHSFQDEKRQLAYQVLGLSEGATNEEIHRSYQELVKVWHPDHNLDQTEEAQRHFLEIQAAYEVLSQPRKPWGSRR

Main question:

I just feel like my original code, although upside down, was more reliable because I didn't have to tell it how many times to print the header, it just looked for and printed only unique headers on its own. Is there a better way to print only new instances of headers but to print all matches of the desired sequence that follows? I could not find a way to specify print only unique matches, and I was uncertain about trying to send all headers and matched regions into a hash (and I have no idea how to do that).

Answer 1

Your question was somewhere in the middle of Code Review und Stack Overflow. I'm going to give you a general review of your code in terms of code quality, and explain about conventions of Perl.

But let's start with things that are good.

• Your code has useful comments. They appear to be more an explanation for the reader here on SE, but they are useful and they show you know what you are doing.
• Your variable names are meaningful, with a few exceptions. Choosing names that speak for themselves is crucial to producing maintainable code.
• The code has indentation. It's not perfect, but it's useful. More below.

Now to things I would suggest to improve.

• Always use strict and use warnings! These pragmas make debugging your code easier. There's nothing in the code that breaks if you turn them on, which is good.

• Use lexical filehandles.

  unless (open FILE, "<", '/scratch/SampleDataFiles/test.fasta')
  

  Here you've already got a three-argument open, which is good, but your FILE filehandle is global. That means it will be seen by modules you use, and there might be a conflict with other code that uses the same name. Instead, use open my $fh, '<', 'filename'.

• You can shorten the unless to an open or die idiom. It's also a good idea to include what didn't work in the error message. If you rerun this program in half a year, Sorry is not going to help you if stuff fails.

  open my $fh, '<', '/scratch/SampleDataFiles/test.fasta' 
      or die "Could not read file test.fasta: $!";
  

• You are reading the whole file into memory with my @file = <FILE> (or $fh). As far as I know, fasta files can be quite big. Since you only ever access one record at a time, reading it line by line (where a line is a record) is way more efficient. Instead of the foreach $file (@file) {}, use a while loop and read directly

  local $/ = ">"; # always localize these changes, see below
  my $count = 0;
  my $sequence_count = 0;
  while ( my $record = <$fh> ) { ... }
  

• When changing variables like the input record separater $/, it is best practice to localize these changes with the local keyword. It makes sure the change only applies to the current scope and all subsequent scopes inside that. A scope is basically the code being executed between a block of { and }, but function calls inside that scope are affected too.

• Do not use the same variable name for different variables in the same scope. You've got $file and @file. Those are two different variables (though they are in the same symbol table, which is like a chest of drawers, but that's probably too detailed). If you wanted to access the first line of @file, that would be $file[0]. You will get confused with that. Instead, the variable $file could be renamed to $record, which also more accurately represents what's in it.

• When indenting your code, be consistent. Always indent each level the same number of spaces (or one tab, if you prefer those). Decide if you want to have whitespace around operators, inside of parenthesis and such. Being consistent is a very important skill to master for software development. I believe it's also important for a biologist or any kind of researcher.

  You've got pos($sequence)-7, and $sequence_count +1 and $count = 0. Decide on one scheme and stick with it.

• Typically people put a whitespace after the # in comments. I think it's a personal preference, but it's very common and I feel strongly about it.

The final code would look like this.

# First, I open my file and die with an error if it fails.
open my $fh, '<', '/scratch/SampleDataFiles/test.fasta'
    or die "Could not open test.fasta: $!";

# changes the record separator from \n to > to read records instead of lines
local $/ = ">";

# here I will count the matched regions
my $count = 0;

# here I will count the sequences that contain a matched region
my $sequence_count = 0;

while ( my $record = <$fh> ) {
    my $temp_count = 0;
    my $count      = 0;

    if ( $record =~ /(.*;.*;?\n)(\w+)/ ) {
        my $head     = $1;
        my $sequence = $2;
        $sequence_count = $sequence_count + 1;

        # Now I use the sequences that I found, and
        # search them for a hydrophobic region.
        while ( $sequence =~ /([VILMFWCA]{8,}?)/gi ) {

            # I use the count variables I made earlier.
            # I count all times I match a sequence that has one
            # or more hydrophobic region.
            $temp_count = $temp_count + 1;

            # But I don't want the header repeated for the same
            # sequence, so I limit thetimes that it can print.
            if ( $temp_count <= 2 ) {
                print "\n", "Hydrophobic region(s) found in ", $head, "\n";
                $count = $count + 1;
            }

            # I want to know what the position of the match is
            # within the sequence.
            my $pos = pos($sequence) - 7;
            print $1, " found at ", $pos, "\n", "\n";
        }
    }
}

print
    "\n", "\n", "-------------------------",
    "\n", "Hydrophobic region(s) found in ", $count,
    " out of ", $sequence_count, " sequences.", "\n", "\n";

Answer 2

What I did was remove the global modifier from sequence match if statement regex, but leave the modifier after the while statement regex. This way I am not losing the first matches like I was before, but I am still able to print the header before the sequence matches.

    unless (open FILE, "<", '/scratch/SampleDataFiles/test.fasta') {
    die "Cannot Open File", $!;
    }

    $/ = ">";       

    my @file = <FILE>;
    my $file = "@file";
    chomp $file;

    my $count = 0;    
    my $sequence_count = 0;   

    foreach $file (@file) {

               if ($file =~ /(.*;.*;?\n)(\w+)/) {

                   my $head = $1;
                   my $sequence = $2;
                   $sequence_count = $sequence_count +1;

                   if ($sequence =~ /([VILMFWCA]{8,}?)/i) {

                            print "\n", "Hydrophobic region(s) found in ", $head, "\n";
                            $count = $count +1;

                   }


                    while ($sequence =~ /([VILMFWCA]{8,}?)/gi) {

                            my $pos = pos($sequence)-7;
                            print $1, " found at ", $pos, "\n", "\n";

                    }
               }
        }


print "\n", "\n", "-------------------------", "\n", "Hydrophobic region(s) 
found in ", $count, " out of ", $sequence_count , " sequences.", "\n", "\n";



close FILE;

Thanks for your help, guys!