Extracting Multiple FASTA Sequences using PHP

This is a simple tutorial which explains how to safely extract multiple sequences from a FASTA file using PHP script. I have used four functions to perform different tasks: read_fas_file() - to check invalid file, fas_check() - to check FASTA file format, get_seq() - to retrieve sequence and sequence name pairs, and fas_get() - to extract and display multiple FASTA file formatted sequences. The full source code and multiple protein sequences in FASTA file format used in this tutorial is given below.

Source Code

function read_fas_file($x) { // Check for Empty File
 if (!file_exists($x)) {
  print "File Not Exist!!";
  exit();
 } else {
  $fh = fopen($x, 'r');
  if (filesize($x) == 0) {
   print "File is Empty!!";
   fclose($fh);
   exit();
  } else {
   $f = fread($fh, filesize($x));
   fclose($fh);
   return $f;
  }
 }
}

function fas_check($x) { // Check FASTA File Format
 $gt = substr($x, 0, 1);
 if ($gt != ">") {
  print "Not FASTA File!!";
  exit();
 } else {
  return $x;
 }
}

function get_seq($x) { // Get Sequence and Sequence Name
 $fl = explode(PHP_EOL, $x);
 $sh = trim(array_shift($fl));
 if($sh == null) {
  $sh = "UNKNOWN SEQUENCE";
 }
 $fl = array_filter($fl);
 $seq = "";
 foreach($fl as $str) {
  $seq .= trim($str);
 }
 $seq = strtoupper($seq);
 $seq = preg_replace("/[^ACDEFGHIKLMNPQRSTVWY]/i", "", $seq);
 if ((count($fl) < 1) || (strlen($seq) == 0)) {
  print "Sequence is Empty!!";
  exit();
 } else {
  return array($sh, $seq);
 }
}

function fas_get($x) { // Read Multiple FASTA Sequences
 $gtr = substr($x, 1);
 $sqs = explode(">", $gtr);
 if (count($sqs) > 1) {
  foreach ($sqs as $sq) {
   $spair = get_seq($sq);
   $spairs[$spair[0]] = $spair[1];
  }
  return $spairs;
 } else {
  $spair = get_seq($gtr);
  return array($spair[0] => $spair[1]);
 }
}

$file = "pdt.fas";
$content = read_fas_file($file);
$fasta = fas_check($content);
$seq = fas_get($fasta);
foreach($seq as $x => $y) {
 print $x . "\n" . $y;
 print "\n\n";
}

FASTA File (pdt.fas)

>pdt|pdtdbt00001|pdb|1OKE|A/B
MRCIGISNRDFVEGVSGGSWVDIVLEHGSCVTTMAKNKPTLDFELIKTEAKQPATLRKYC
IEAKLTNTTTESRCPTQGEPTLNEEQDKRFVCKHSMVDRGWGNGCGLFGKGGIVTCAMFT
CKKNMEGKIVQPENLEYTVVITPHSGEEHAVGNDTGKHGKEVKITPQSSITEAELTGYGT
VTMECSPRTGLDFNEMVLLQMKDKAWLVHRQWFLDLPLPWLPGADTQGSNWIQKETLVTF
KNPHAKKQDVVVLGSQEGAMHTALTGATEIQMSSGNLLFTGHLKCRLRMDKLQLKGMSYS
MCTGKFKVVKEIAETQHGTIVIRVQYEGDGSPCKIPFEIMDLEKRHVLGRLITVNPIVTE
KDSPVNIEAEPPFGDSYIIIGVEPGQLKLNWFKK
>pdt|pdtdbt00002|pdb|4O6B|A/B
AHHHHHHSSGVDLGTENLYFQSNADSGCVVSWKNKELKCGSGIFITDNVHTWTEQYKFQP
ESPSKLASAIQKAHEEGICGIRSVTRLENLMWKQITPELNHILSENEVKLTIMTGDIKGI
MQAGKRSLRPQPTELKYSWKTWGKAKMLSTESHNQTFLIDGPETAECPNTNRAWNSLEVE
DYGFGVFTTNIWLKLKEKQDVFCDSKLMSAAIKDNRAVHADMGYWIESALNDTWKIEKAS
FIEVKNCHWPKSHTLWSNGVLESEMIIPKNLAGPVSQHNYRPGYHTQITGPWHLGKLEMD
FDFCDGTTVVVTEDCGNRGPSLRTTTASGKLITEWCCRSCTLPPLRYRGEDGCWYGMEIR
PLKEKEENLVNSLVTA
>pdt|pdtdbt00003|pdb|2IOK|A/B
SKKNSLALSLTADQMVSALLDAEPPILYSEYDPTRPFSEASMMGLLTNLADRELVHMINW
AKRVPGFVDLTLHDQVHLLECAWLEILMIGLVWRSMEHPGKLLFAPNLLLDRNQGKCVEG
MVEIFDMLLATSSRFRMMNLQGEEFVCLKSIILLNSGVYTFLSSTLKSLEEKDHIHRVLD
KITDTLIHLMAKAGLTLQQQHQRLAQLLLILSHIRHMSNKGMEHLYSMKCKNVVPLYDLL
LEMLDAHRLHAPTS
>pdt|pdtdbt00004|pdb|2Q1Y|A/B
MTPPHNYLAVIKVVGIGGGGVNAVNRMIEQGLKGVEFIAINTDAQALLMSDADVKLDVGR
DSTRGLGAGADPEVGRKAAEDAKDEIEELLRGADMVFVTAGEGGGTGTGGAPVVASIARK
LGALTVGVVTRPFSFEGKRRSNQAENGIAALRESCDTLIVIPNDRLLQMGDAAVSLMDAF
RSADEVLLNGVQGITDLITTPGLINVDFADVKGIMSGAGTALMGIGSARGEGRSLKAAEI
AINSPLLEASMEGAQGVLMSIAGGSDLGLFEINEAASLVQDAAHPDANIIFGTVIDDSLG
DEVRVTVIAAGFDVSGPGRKPVMGETGGAHRIESAKAGKLTSTLFEPVDAVSVPLHTNGA
TLSIGGDDDDVDVPPFMRR
>pdt|pdtdbt00005|pdb|3GGE|A/B/C
SMKGIEKEVNVYKSEDSLGLTITDNGVGYAFIKRIKDGGVIDSVKTICVGDHIESINGEN
IVGWRHYDVAKKLKELKKEELFTMKLIEPKKSSEA
>pdt|pdtdbt00006|pdb|2F9Q|A/B/C/D
MAKKTSSKGKLPPGPLPLPGLGNLLHVDFQNTPYCFDQLRRRFGDVFSLQLAWTPVVVLN
GLAAVREALVTHGEDTADRPPVPITQILGFGPRSQGVFLARYGPAWREQRRFSVSTLRNL
GLGKKSLEQWVTEEAACLCAAFANHSGRPFRPNGLLDKAVSNVIASLTCGRRFEYDDPRF
LRLLDLAQEGLKEESGFLREVLNAVPVDRHIPALAGKVLRFQKAFLTQLDELLTEHRMTW
DPAQPPRDLTEAFLAEMEKAKGNPESSFNDENLRIVVADLFSAGMVTTSTTLAWGLLLMI
LHPDVQRRVQQEIDDVIGQVRRPEMGDQAHMPYTTAVIHEVQRFGDIVPLGMTHMTSRDI
EVQGFRIPKGTTLITNLSSVLKDEAVWEKPFRFHPEHFLDAQGHFVKPEAFLPFSAGRRA
CLGEPLARMELFLFFTSLLQHFSFSVPTGQPRPSHHGVFAFLVSPSPYELCAVPRHHHH
>pdt|pdtdbt00007|pdb|3EAH|A/B
PKFPRVKNWEVGSITYDTLSAQAQQDGPCTPRRCLGSLVFPRKLQGRPSPGPPAPEQLLS
QARDFINQYYSSIKRSGSQAHEQRLQEVEAEVAATGTYQLRESELVFGAKQAWRNAPRCV
GRIQWGKLQVFDARDCRSAQEMFTYICNHIKYATNRGNLRSAITVFPQRCPGRGDFRIWN
SQLVRYAGYRQQDGSVRGDPANVEITELCIQHGWTPGNGRFDVLPLLLQAPDEPPELFLL
PPELVLEVPLEHPTLEWFAALGLRWYALPAVSNMLLEIGGLEFPAAPFSGWYMSTEIGTR
NLCDPHRYNILEDVAVCMDLDTRTTSSLWKDKAAVEINVAVLHSYQLAKVTIVDHHAATA
SFMKHLENEQKARGGCPADWAWIVPPISGSLTPVFHQEMVNYFLSPAFRYQPDPWKGSAA
KGTGITR
>pdt|pdtdbt00008|pdb|4PQE|A
EGREDAELLVTVRGGRLRGIRLKTPGGPVSAFLGIPFAEPPMGPRRFLPPEPKQPWSGVV
DATTFQSVCYQYVDTLYPGFEGTEMWNPNRELSEDCLYLNVWTPYPRPTSPTPVLVWIYG
GGFYSGASSLDVYDGRFLVQAERTVLVSMNYRVGAFGFLALPGSREAPGNVGLLDQRLAL
QWVQENVAAFGGDPTSVTLFGESAGAASVGMHLLSPPSRGLFHRAVLQSGAPNGPWATVG
MGEARRRATQLAHLVGCPPGGTGGNDTELVACLRTRPAQVLVNHEWHVLPQESVFRFSFV
PVVDGDFLSDTPEALINAGDFHGLQVLVGVVKDEGSYFLVYGAPGFSKDNESLISRAEFL
AGVRVGVPQVSDLAAEAVVLHYTDWLHPEDPARLREALSDVVGDHNVVCPVAQLAGRLAA
QGARVYAYVFEHRASTLSWPLWMGVPHGYEIEFIFGIPLDPSRNYTAEEKIFAQRLMRYW
ANFARTGDPNEPRDPKAPQWPPYTAGAQQYVSLDLRPLEVRRGLRAQACAFWNRFLPKLL
SAT