不废话，直接说功能
1.重定向，语法：
header("location:http://www.lemon-x.ga");
file_put_contents("./test.txt","我还执行");
此函数不会妨碍下面的代码执行。
2.可以做到每次都是重新获取页面，不会从缓存中加载，用户可能会设置一些选项来更改浏览器的默认缓存设置。通过发送上面的报头，您可以覆盖任何这些设置，强制浏览器不进行缓存！
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); header("Cache-Control: no-cache"); header("Pragma: no-cache");
3.提供下载文件
header('Content-type: application/image/pjpeg');//输出文件的格式 header('Content-Disposition: attachment;filename="demo.jpg"'); //下载显示的名字，注意格式。 readfile('my.jpg');//指定下载文件的路径
下面的是用来写在文件头上的，来确定该文件是什么类型。
'chm'=>'application/octet-stream',
'ppt'=>'application/vnd.ms-powerpoint',
'xls'=>'application/vnd.ms-excel',
'doc'=>'application/msword',
'exe'=>'application/octet-stream',
'rar'=>'application/octet-stream',
'js'=>"javascript/js",
'css'=>"text/css",
'hqx'=>"application/mac-binhex40",
'bin'=>"application/octet-stream",
'oda'=>"application/oda",
'pdf'=>"application/pdf",
'ai'=>"application/postsrcipt",
'eps'=>"application/postsrcipt",
'es'=>"application/postsrcipt",
'rtf'=>"application/rtf",
'mif'=>"application/x-mif",
'csh'=>"application/x-csh",
'dvi'=>"application/x-dvi",
'hdf'=>"application/x-hdf",
'nc'=>"application/x-netcdf",
'cdf'=>"application/x-netcdf",
'latex'=>"application/x-latex",
'ts'=>"application/x-troll-ts",
'src'=>"application/x-wais-source",
'zip'=>"application/zip",
'bcpio'=>"application/x-bcpio",
'cpio'=>"application/x-cpio",
'gtar'=>"application/x-gtar",
'shar'=>"application/x-shar",
'sv4cpio'=>"application/x-sv4cpio",
'sv4crc'=>"application/x-sv4crc",
'tar'=>"application/x-tar",
'ustar'=>"application/x-ustar",
'man'=>"application/x-troff-man",
'sh'=>"application/x-sh",
'tcl'=>"application/x-tcl",
'tex'=>"application/x-tex",
'texi'=>"application/x-texinfo",
'texinfo'=>"application/x-texinfo",
't'=>"application/x-troff",
'tr'=>"application/x-troff",
'roff'=>"application/x-troff",
'shar'=>"application/x-shar",
'me'=>"application/x-troll-me",
'ts'=>"application/x-troll-ts",
'gif'=>"image/gif",
'jpeg'=>"image/pjpeg",
'jpg'=>"image/pjpeg",
'jpe'=>"image/pjpeg",
'ras'=>"image/x-cmu-raster",
'pbm'=>"image/x-portable-bitmap",
'ppm'=>"image/x-portable-pixmap",
'xbm'=>"image/x-xbitmap",
'xwd'=>"image/x-xwindowdump",
'ief'=>"image/ief",
'tif'=>"image/tiff",
'tiff'=>"image/tiff",
'pnm'=>"image/x-portable-anymap",
'pgm'=>"image/x-portable-graymap",
'rgb'=>"image/x-rgb",
'xpm'=>"image/x-xpixmap",
'txt'=>"text/plain",
'c'=>"text/plain",
'cc'=>"text/plain",
'h'=>"text/plain",
'html'=>"text/html",
'htm'=>"text/html",
'htl'=>"text/html",
'rtx'=>"text/richtext",
'etx'=>"text/x-setext",
'tsv'=>"text/tab-separated-values",
'mpeg'=>"video/mpeg",
'mpg'=>"video/mpeg",
'mpe'=>"video/mpeg",
'avi'=>"video/x-msvideo",
'qt'=>"video/quicktime",
'mov'=>"video/quicktime",
'moov'=>"video/quicktime",
'movie'=>"video/x-sgi-movie",
'au'=>"audio/basic",
'snd'=>"audio/basic",
'wav'=>"audio/x-wav",
'aif'=>"audio/x-aiff",
'aiff'=>"audio/x-aiff",
'aifc'=>"audio/x-aiff",
'swf'=>"application/x-shockwave-flash"
'myz'=>"application/myz"
".*"="application/octet-stream"
".001"="application/x-001"
".301"="application/x-301"
".323"="text/h323"
".906"="application/x-906"
".907"="drawing/907"
".a11"="application/x-a11"
".acp"="audio/x-mei-aac"
".ai"="application/postscript"
".aif"="audio/aiff"
".aifc"="audio/aiff"
".aiff"="audio/aiff"
".anv"="application/x-anv"
".asa"="text/asa"
".asf"="video/x-ms-asf"
".asp"="text/asp"
".asx"="video/x-ms-asf"
".au"="audio/basic"
".avi"="video/avi"
".awf"="application/vnd.adobe.workflow"
".biz"="text/xml"
".bmp"="application/x-bmp"
".bot"="application/x-bot"
".c4t"="application/x-c4t"
".c90"="application/x-c90"
".cal"="application/x-cals"
".cat"="application/vnd.ms-pki.seccat"
".cdf"="application/x-netcdf"
".cdr"="application/x-cdr"
".cel"="application/x-cel"
".cer"="application/x-x509-ca-cert"
".cg4"="application/x-g4"
".cgm"="application/x-cgm"
".cit"="application/x-cit"
".class"="java/*"
".cml"="text/xml"
".cmp"="application/x-cmp"
".cmx"="application/x-cmx"
".cot"="application/x-cot"
".crl"="application/pkix-crl"
".crt"="application/x-x509-ca-cert"
".csi"="application/x-csi"
".css"="text/css"
".cut"="application/x-cut"
".dbf"="application/x-dbf"
".dbm"="application/x-dbm"
".dbx"="application/x-dbx"
".dcd"="text/xml"
".dcx"="application/x-dcx"
".der"="application/x-x509-ca-cert"
".dgn"="application/x-dgn"
".dib"="application/x-dib"
".dll"="application/x-msdownload"
".doc"="application/msword"
".dot"="application/msword"
".drw"="application/x-drw"
".dtd"="text/xml"
".dwf"="Model/vnd.dwf"
".dwf"="application/x-dwf"
".dwg"="application/x-dwg"
".dxb"="application/x-dxb"
".dxf"="application/x-dxf"
".edn"="application/vnd.adobe.edn"
".emf"="application/x-emf"
".eml"="message/rfc822"
".ent"="text/xml"
".epi"="application/x-epi"
".eps"="application/x-ps"
".eps"="application/postscript"
".etd"="application/x-ebx"
".exe"="application/x-msdownload"
".fax"="image/fax"
".fdf"="application/vnd.fdf"
".fif"="application/fractals"
".fo"="text/xml"
".frm"="application/x-frm"
".g4"="application/x-g4"
".gbr"="application/x-gbr"
".gcd"="application/x-gcd"
".gif"="image/gif"
".gl2"="application/x-gl2"
".gp4"="application/x-gp4"
".hgl"="application/x-hgl"
".hmr"="application/x-hmr"
".hpg"="application/x-hpgl"
".hpl"="application/x-hpl"
".hqx"="application/mac-binhex40"
".hrf"="application/x-hrf"
".hta"="application/hta"
".htc"="text/x-component"
".htm"="text/html"
".html"="text/html"
".htt"="text/webviewhtml"
".htx"="text/html"
".icb"="application/x-icb"
".ico"="image/x-icon"
".ico"="application/x-ico"
".iff"="application/x-iff"
".ig4"="application/x-g4"
".igs"="application/x-igs"
".iii"="application/x-iphone"
".img"="application/x-img"
".ins"="application/x-internet-signup"
".isp"="application/x-internet-signup"
".IVF"="video/x-ivf"
".java"="java/*"
".jfif"="image/jpeg"
".jpe"="image/jpeg"
".jpe"="application/x-jpe"
".jpeg"="image/jpeg"
".jpg"="image/jpeg"
".jpg"="application/x-jpg"
".js"="application/x-javascript"
".jsp"="text/html"
".la1"="audio/x-liquid-file"
".lar"="application/x-laplayer-reg"
".latex"="application/x-latex"
".lavs"="audio/x-liquid-secure"
".lbm"="application/x-lbm"
".lmsff"="audio/x-la-lms"
".ls"="application/x-javascript"
".ltr"="application/x-ltr"
".m1v"="video/x-mpeg"
".m2v"="video/x-mpeg"
".m3u"="url"
".m4e"="video/mpeg4"
".mac"="application/x-mac"
".man"="application/x-troff-man"
".math"="text/xml"
".mdb"="application/msaccess"
".mdb"="application/x-mdb"
".mfp"="application/x-shockwave-flash"
".mht"="message/rfc822"
".mhtml"="message/rfc822"
".mi"="application/x-mi"
".mid"="audio/mid"
".midi"="audio/mid"
".mil"="application/x-mil"
".mml"="text/xml"
".mnd"="audio/x-musicnet-download"
".mns"="audio/x-musicnet-stream"
".mocha"="application/x-javascript"
".movie"="video/x-sgi-movie"
".mp1"="audio/mp1"
".mp2"="audio/mp2"
".mp2v"="video/mpeg"
".mp3"="audio/mp3"
".mp4"="video/mpeg4"
".mpa"="video/x-mpg"
".mpd"="application/vnd.ms-project"
".mpe"="video/x-mpeg"
".mpeg"="video/mpg"
".mpg"="video/mpg"
".mpga"="audio/rn-mpeg"
".mpp"="application/vnd.ms-project"
".mps"="video/x-mpeg"
".mpt"="application/vnd.ms-project"
".mpv"="video/mpg"
".mpv2"="video/mpeg"
".mpw"="application/vnd.ms-project"
".mpx"="application/vnd.ms-project"
".mtx"="text/xml"
".mxp"="application/x-mmxp"
".net"="image/pnetvue"
".nrf"="application/x-nrf"
".nws"="message/rfc822"
".odc"="text/x-ms-odc"
".out"="application/x-out"
".p10"="application/pkcs10"
".p12"="application/x-pkcs12"
".p7b"="application/x-pkcs7-certificates"
".p7c"="application/pkcs7-mime"
".p7m"="application/pkcs7-mime"
".p7r"="application/x-pkcs7-certreqresp"
".p7s"="application/pkcs7-signature"
".pc5"="application/x-pc5"
".pci"="application/x-pci"
".pcl"="application/x-pcl"
".pcx"="application/x-pcx"
".pdf"="application/pdf"
".pdf"="application/pdf"
".pdx"="application/vnd.adobe.pdx"
".pfx"="application/x-pkcs12"
".pgl"="application/x-pgl"
".pic"="application/x-pic"
".pko"="application/vnd.ms-pki.pko"
".pl"="application/x-perl"
".plg"="text/html"
".pls"="audio/scpls"
".plt"="application/x-plt"
".png"="image/png"
".png"="application/x-png"
".pot"="application/vnd.ms-powerpoint"
".ppa"="application/vnd.ms-powerpoint"
".ppm"="application/x-ppm"
".pps"="application/vnd.ms-powerpoint"
".ppt"="application/vnd.ms-powerpoint"
".ppt"="application/x-ppt"
".pr"="application/x-pr"
".prf"="application/pics-rules"
".prn"="application/x-prn"
".prt"="application/x-prt"
".ps"="application/x-ps"
".ps"="application/postscript"
".ptn"="application/x-ptn"
".pwz"="application/vnd.ms-powerpoint"
".r3t"="text/vnd.rn-realtext3d"
".ra"="audio/vnd.rn-realaudio"
".ram"="audio/x-pn-realaudio"
".ras"="application/x-ras"
".rat"="application/rat-file"
".rdf"="text/xml"
".rec"="application/vnd.rn-recording"
".red"="application/x-red"
".rgb"="application/x-rgb"
".rjs"="application/vnd.rn-realsystem-rjs"
".rjt"="application/vnd.rn-realsystem-rjt"
".rlc"="application/x-rlc"
".rle"="application/x-rle"
".rm"="application/vnd.rn-realmedia"
".rmf"="application/vnd.adobe.rmf"
".rmi"="audio/mid"
".rmj"="application/vnd.rn-realsystem-rmj"
".rmm"="audio/x-pn-realaudio"
".rmp"="application/vnd.rn-rn_music_package"
".rms"="application/vnd.rn-realmedia-secure"
".rmvb"="application/vnd.rn-realmedia-vbr"
".rmx"="application/vnd.rn-realsystem-rmx"
".rnx"="application/vnd.rn-realplayer"
".rp"="image/vnd.rn-realpix"
".rpm"="audio/x-pn-realaudio-plugin"
".rsml"="application/vnd.rn-rsml"
".rt"="text/vnd.rn-realtext"
".rtf"="application/msword"
".rtf"="application/x-rtf"
".rv"="video/vnd.rn-realvideo"
".sam"="application/x-sam"
".sat"="application/x-sat"
".sdp"="application/sdp"
".sdw"="application/x-sdw"
".sit"="application/x-stuffit"
".slb"="application/x-slb"
".sld"="application/x-sld"
".slk"="drawing/x-slk"
".smi"="application/smil"
".smil"="application/smil"
".smk"="application/x-smk"
".snd"="audio/basic"
".sol"="text/plain"
".sor"="text/plain"
".spc"="application/x-pkcs7-certificates"
".spl"="application/futuresplash"
".spp"="text/xml"
".ssm"="application/streamingmedia"
".sst"="application/vnd.ms-pki.certstore"
".stl"="application/vnd.ms-pki.stl"
".stm"="text/html"
".sty"="application/x-sty"
".svg"="text/xml"
".swf"="application/x-shockwave-flash"
".tdf"="application/x-tdf"
".tg4"="application/x-tg4"
".tga"="application/x-tga"
".tif"="image/tiff"
".tif"="application/x-tif"
".tiff"="image/tiff"
".tld"="text/xml"
".top"="drawing/x-top"
".torrent"="application/x-bittorrent"
".tsd"="text/xml"
".txt"="text/plain"
".uin"="application/x-icq"
".uls"="text/iuls"
".vcf"="text/x-vcard"
".vda"="application/x-vda"
".vdx"="application/vnd.visio"
".vml"="text/xml"
".vpg"="application/x-vpeg005"
".vsd"="application/vnd.visio"
".vsd"="application/x-vsd"
".vss"="application/vnd.visio"
".vst"="application/vnd.visio"
".vst"="application/x-vst"
".vsw"="application/vnd.visio"
".vsx"="application/vnd.visio"
".vtx"="application/vnd.visio"
".vxml"="text/xml"
".wav"="audio/wav"
".wax"="audio/x-ms-wax"
".wb1"="application/x-wb1"
".wb2"="application/x-wb2"
".wb3"="application/x-wb3"
".wbmp"="image/vnd.wap.wbmp"
".wiz"="application/msword"
".wk3"="application/x-wk3"
".wk4"="application/x-wk4"
".wkq"="application/x-wkq"
".wks"="application/x-wks"
".wm"="video/x-ms-wm"
".wma"="audio/x-ms-wma"
".wmd"="application/x-ms-wmd"
".wmf"="application/x-wmf"
".wml"="text/vnd.wap.wml"
".wmv"="video/x-ms-wmv"
".wmx"="video/x-ms-wmx"
".wmz"="application/x-ms-wmz"
".wp6"="application/x-wp6"
".wpd"="application/x-wpd"
".wpg"="application/x-wpg"
".wpl"="application/vnd.ms-wpl"
".wq1"="application/x-wq1"
".wr1"="application/x-wr1"
".wri"="application/x-wri"
".wrk"="application/x-wrk"
".ws"="application/x-ws"
".ws2"="application/x-ws"
".wsc"="text/scriptlet"
".wsdl"="text/xml"
".wvx"="video/x-ms-wvx"
".xdp"="application/vnd.adobe.xdp"
".xdr"="text/xml"
".xfd"="application/vnd.adobe.xfd"
".xfdf"="application/vnd.adobe.xfdf"
".xhtml"="text/html"
".xls"="application/vnd.ms-excel"
".xls"="application/x-xls"
".xlw"="application/x-xlw"
".xml"="text/xml"
".xpl"="audio/scpls"
".xq"="text/xml"
".xql"="text/xml"
".xquery"="text/xml"
".xsd"="text/xml"
".xsl"="text/xml"
".xslt"="text/xml"
".xwd"="application/x-xwd"
".x_b"="application/x-x_b"
".x_t"="application/x-x_t"
".myz"="application/myz"