使用wget工具抓取网页和图片
jopen
10年前
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 <bug-wget@gnu.org>.
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Freestyletime@foxmail.com，欢迎交流。
来自：http://my.oschina.net/freestyletime/blog/356985