奇怪的需求

公司需要将服务器的网页缓存到路由器，用户在访问该网页时就直接取路由器上的缓存即可。虽然我不知道这个需求有什么意义，但还是尽力去实现吧。

wget概述

wget是unix和类unix下的一个网页抓取工具，待我熟悉它后，发现它的功能远不止这些。但是这篇博文只说怎么抓取一个指定URL以及它下面的相关内容（包括html,js,css,图片）并将内容里的绝对路径换成相对路径。网上搜到一堆有关wget的文章，关于它怎么抓取网页和相关的图片资源，反正我是没有找到一篇实用的，都以失败告终。

这是wget -h > ./help_wget.txt 后的文件内容

GNU Wget 1.16, a non-interactive network retriever.

Usage: wget [OPTION]... [URL]...

Mandatory arguments to long options are mandatory for short options too.



Startup:

  -V,  --version                   display the version of Wget and exit.

  -h,  --help                      print this help.

  -b,  --background                go to background after startup.

  -e,  --execute=COMMAND           execute a `.wgetrc‘-style command.



Logging and input file:

  -o,  --output-file=FILE          log messages to FILE.

  -a,  --append-output=FILE        append messages to FILE.

  -q,  --quiet                     quiet (no output).

  -v,  --verbose                   be verbose (this is the default).

  -nv, --no-verbose                turn off verboseness, without being quiet.

       --report-speed=TYPE         Output bandwidth as TYPE.  TYPE can be bits.

  -i,  --input-file=FILE           download URLs found in local or external FILE.

  -F,  --force-html                treat input file as HTML.

  -B,  --base=URL                  resolves HTML input-file links (-i -F)

                                   relative to URL.

       --config=FILE               Specify config file to use.

       --no-config                 Do not read any config file.

Download:

  -t,  --tries=NUMBER              set number of retries to NUMBER (0 unlimits).

       --retry-connrefused         retry even if connection is refused.

  -O,  --output-document=FILE      write documents to FILE.

  -nc, --no-clobber                skip downloads that would download to

                                   existing files (overwriting them).

  -c,  --continue                  resume getting a partially-downloaded file.

       --start-pos=OFFSET          start downloading from zero-based position OFFSET.

       --progress=TYPE             select progress gauge type.

       --show-progress             display the progress bar in any verbosity mode.

  -N,  --timestamping              don‘t re-retrieve files unless newer than

                                   local.

  --no-use-server-timestamps       don‘t set the local file‘s timestamp by

                                   the one on the server.

  -S,  --server-response           print server response.

       --spider                    don‘t download anything.

  -T,  --timeout=SECONDS           set all timeout values to SECONDS.

       --dns-timeout=SECS          set the DNS lookup timeout to SECS.

       --connect-timeout=SECS      set the connect timeout to SECS.

       --read-timeout=SECS         set the read timeout to SECS.

  -w,  --wait=SECONDS              wait SECONDS between retrievals.

       --waitretry=SECONDS         wait 1..SECONDS between retries of a retrieval.

       --random-wait               wait from 0.5*WAIT...1.5*WAIT secs between retrievals.

       --no-proxy                  explicitly turn off proxy.

  -Q,  --quota=NUMBER              set retrieval quota to NUMBER.

       --bind-address=ADDRESS      bind to ADDRESS (hostname or IP) on local host.

       --limit-rate=RATE           limit download rate to RATE.

       --no-dns-cache              disable caching DNS lookups.

       --restrict-file-names=OS    restrict chars in file names to ones OS allows.

       --ignore-case               ignore case when matching files/directories.

  -4,  --inet4-only                connect only to IPv4 addresses.

  -6,  --inet6-only                connect only to IPv6 addresses.

       --prefer-family=FAMILY      connect first to addresses of specified family,

                                   one of IPv6, IPv4, or none.

       --user=USER                 set both ftp and http user to USER.

       --password=PASS             set both ftp and http password to PASS.

       --ask-password              prompt for passwords.

       --no-iri                    turn off IRI support.

       --local-encoding=ENC        use ENC as the local encoding for IRIs.

       --remote-encoding=ENC       use ENC as the default remote encoding.

       --unlink                    remove file before clobber.



Directories:

  -nd, --no-directories            don‘t create directories.

  -x,  --force-directories         force creation of directories.

  -nH, --no-host-directories       don‘t create host directories.

       --protocol-directories      use protocol name in directories.

  -P,  --directory-prefix=PREFIX   save files to PREFIX/...

       --cut-dirs=NUMBER           ignore NUMBER remote directory components.



HTTP options:

       --http-user=USER            set http user to USER.

       --http-password=PASS        set http password to PASS.

       --no-cache                  disallow server-cached data.

       --default-page=NAME         Change the default page name (normally

                                   this is `index.html‘.).

  -E,  --adjust-extension          save HTML/CSS documents with proper extensions.

       --ignore-length             ignore `Content-Length‘ header field.

       --header=STRING             insert STRING among the headers.

       --max-redirect              maximum redirections allowed per page.

       --proxy-user=USER           set USER as proxy username.

       --proxy-password=PASS       set PASS as proxy password.

       --referer=URL               include `Referer: URL‘ header in HTTP request.

       --save-headers              save the HTTP headers to file.

  -U,  --user-agent=AGENT          identify as AGENT instead of Wget/VERSION.

       --no-http-keep-alive        disable HTTP keep-alive (persistent connections).

       --no-cookies                don‘t use cookies.

       --load-cookies=FILE         load cookies from FILE before session.

       --save-cookies=FILE         save cookies to FILE after session.

       --keep-session-cookies      load and save session (non-permanent) cookies.

       --post-data=STRING          use the POST method; send STRING as the data.

       --post-file=FILE            use the POST method; send contents of FILE.

       --method=HTTPMethod         use method "HTTPMethod" in the request.

       --body-data=STRING          Send STRING as data. --method MUST be set.

       --body-file=FILE            Send contents of FILE. --method MUST be set.

       --content-disposition       honor the Content-Disposition header when

                                   choosing local file names (EXPERIMENTAL).

       --content-on-error          output the received content on server errors.

       --auth-no-challenge         send Basic HTTP authentication information

                                   without first waiting for the server‘s

                                   challenge.



HTTPS (SSL/TLS) options:

       --secure-protocol=PR        choose secure protocol, one of auto, SSLv2,

                                   SSLv3, TLSv1 and PFS.

       --https-only                only follow secure HTTPS links

       --no-check-certificate      don‘t validate the server‘s certificate.

       --certificate=FILE          client certificate file.

       --certificate-type=TYPE     client certificate type, PEM or DER.

       --private-key=FILE          private key file.

       --private-key-type=TYPE     private key type, PEM or DER.

       --ca-certificate=FILE       file with the bundle of CA‘s.

       --ca-directory=DIR          directory where hash list of CA‘s is stored.

       --random-file=FILE          file with random data for seeding the SSL PRNG.

       --egd-file=FILE             file naming the EGD socket with random data.



FTP options:

       --ftp-user=USER             set ftp user to USER.

       --ftp-password=PASS         set ftp password to PASS.

       --no-remove-listing         don‘t remove `.listing‘ files.

       --no-glob                   turn off FTP file name globbing.

       --no-passive-ftp            disable the "passive" transfer mode.

       --preserve-permissions      preserve remote file permissions.

       --retr-symlinks             when recursing, get linked-to files (not dir).



WARC options:

       --warc-file=FILENAME        save request/response data to a .warc.gz file.

       --warc-header=STRING        insert STRING into the warcinfo record.

       --warc-max-size=NUMBER      set maximum size of WARC files to NUMBER.

       --warc-cdx                  write CDX index files.

       --warc-dedup=FILENAME       do not store records listed in this CDX file.

       --no-warc-compression       do not compress WARC files with GZIP.

       --no-warc-digests           do not calculate SHA1 digests.

       --no-warc-keep-log          do not store the log file in a WARC record.

       --warc-tempdir=DIRECTORY    location for temporary files created by the

                                   WARC writer.



Recursive download:

  -r,  --recursive                 specify recursive download.

  -l,  --level=NUMBER              maximum recursion depth (inf or 0 for infinite).

       --delete-after              delete files locally after downloading them.

  -k,  --convert-links             make links in downloaded HTML or CSS point to

                                   local files.

       --backups=N                 before writing file X, rotate up to N backup files.

  -K,  --backup-converted          before converting file X, back up as X.orig.

  -m,  --mirror                    shortcut for -N -r -l inf --no-remove-listing.

  -p,  --page-requisites           get all images, etc. needed to display HTML page.

       --strict-comments           turn on strict (SGML) handling of HTML comments.



Recursive accept/reject:

  -A,  --accept=LIST               comma-separated list of accepted extensions.

  -R,  --reject=LIST               comma-separated list of rejected extensions.

       --accept-regex=REGEX        regex matching accepted URLs.

       --reject-regex=REGEX        regex matching rejected URLs.

       --regex-type=TYPE           regex type (posix).

  -D,  --domains=LIST              comma-separated list of accepted domains.

       --exclude-domains=LIST      comma-separated list of rejected domains.

       --follow-ftp                follow FTP links from HTML documents.

       --follow-tags=LIST          comma-separated list of followed HTML tags.

       --ignore-tags=LIST          comma-separated list of ignored HTML tags.

  -H,  --span-hosts                go to foreign hosts when recursive.

  -L,  --relative                  follow relative links only.

  -I,  --include-directories=LIST  list of allowed directories.

       --trust-server-names  use the name specified by the redirection

                                   url last component.

  -X,  --exclude-directories=LIST  list of excluded directories.

  -np, --no-parent   don‘t ascend to the parent directory.


Mail bug reports and suggestions to <[email protected]>.

wget尝试

根据wget的帮助文档，我尝试了下面这条命令

wget -r -np -pk -nH -P ./download http://www.baidu.com

-r  递归下载所有内容

-np 只下载给定URL下的内容，不下载它的上级内容

-p 下载有关页面需要用到的所有资源，包括图片和css样式

-k 将绝对路径转换为相对路径（这个很重要，为了在用户打开网页的时候，加载的相关资源都在本地寻找）

-nH 禁止wget以接收的URL为名称创建文件夹（如果没有这个，这条命令会将下载的内容存在./download/www.baidu.com/下）

-P 下载到哪个路径，这里是当前文件夹下的download文件夹下，没有的话，wget会帮你自动创建

这些选项都符合目前的这个需求，单结果很意外，并不是我们想象的那么简单，wget并没有给我们想要的东西

你如果执行了这条命令，会发现在当前的download文件夹中只是下载了一个index.html和一个robots.txt，而index.html文件所需要的图片也并没有被下载

<img>标签中的路径也没有被替换成相对路径，可能只是去掉了"http:"这个字符串而已。

至于为什么会这样，请继续往下看。

wget正解

因为上面的命令行不通，所以，脑洞全开。来吧，让我们写一个shell脚本，名称为wget_cc内容如下

#!/bin/sh

URL="$2"
PATH="$1"

echo "download url: $URL"
echo "download dir: $PATH"

/usr/bin/wget -e robots=off -w 1 -xq -np -nH -pk -m  -t 1 -P "$PATH" "$URL"

echo "success to download"

这里多加了几个参数，解释一下：

-e 用法是‘-e command’

    用来执行额外的.wgetrc命令。就像vim的配置存在.vimrc文件中一样，wget也用.wgetrc文件来存放它的配置。也就是说在wget执行之前，会先执行.wgetrc文件中的配置命令。一个典型的.wgetrc文件可以参考：

    http://www.gnu.org/software/wget/manual/html_node/Sample-Wgetrc.html 

    http://www.gnu.org/software/wget/manual/html_node/Wgetrc-Commands.html

    用户可以在不改写.wgetrc文件的情况下，用-e选项指定额外的配置命令。如果想要制定多个配置命令，-e command1 -e command2 ... -e commandN即可。这些制定的配置命令，会在.wgetrc中所有命令之后执行，因此会覆盖.wgetrc中相同的配置项。

    这里robots=off是因为wget默认会根据网站的robots.txt进行操作，如果robots.txt里是User-agent: * Disallow: /的话，wget是做不了镜像或者下载目录的。

    这就是前面为什么下载不了图片和其他资源的原因所在了，因为你要爬的HOST禁止蜘蛛去爬它，而wget使用 -e robots=off 这个选项可以通过这个命令绕过这个限制。

-x 创建镜像网站对应的目录结构

-q 静默下载，即不显示下载信息，你如果想知道wget当前在下载什么资源的话，可以去掉这个选项

-m 它会打开镜像相关的选项，比如无限深度的子目录递归下载。

-t times 某个资源下载失败后的重试下载次数

-w seconds 资源请求下载之间的等待时间（减轻服务器的压力）

剩下有不懂的你就去挖文档吧。

写好后保存退出，执行：

chmod 744 wget_cc

下面就让脚本执行起来吧！

./wget_cc ./download http://www.baidu.com

OK，然后再查看<img>标签中的src属性，

src="img/bd_logo1.png"

果然换成了相对路径啊，大功告成，觉得对您有帮助的请点个赞吧！

这里是[email protected]，欢迎交流。

本人原创作品，转载请标明出处。