Linux 提供两个非常实用的命令来爬取网页，来判断网站的连通性，它们分别是 curl 和 wget。今天我们主要重点说一下curl。包括查看网页源码，自动跳转，显示头部信息等功能和curl 命令完整的参数。
直接在 curl 命令后加上网址，就可以看到网页源码。以网址 www.kkpan.com为例（选择该网址，主要因为它的网页代码较短）。
$ curl www.kkpan.com <html> <head><title>301 Moved Permanently</title></head> <body bgcolor="white"> <center><h1>301 Moved Permanently</h1></center> <hr><center>nginx</center> </body> </html>
如果要把这个网页保存下来，可以使用 -o 参数：
$ curl -o [文件名] www.kkpan.com
有的网址是自动跳转的。使用 -L 参数，curl 就会跳转到新的网址。
$ curl -L www.kkpan.com
键入上面的命令，结果自动跳转为 www.kkpan.com.cn。
-i 参数可以显示 http response 的头信息，连同网页代码一起。-I 参数则只显示 http response 的头信息。
$ curl -i www.kkpan.com HTTP/1.1 301 Moved Permanently Server: nginx Date: Tue, 23 Aug 2016 08:30:16 GMT Content-Type: text/html Location: http://www.kkpan.com.cn/ Expires: Tue, 23 Aug 2016 08:32:16 GMT Cache-Control: max-age=120 Age: 102 Content-Length: 178 X-Cache: HIT from xd33-83.kkpan.com.cn <html> <head><title>301 Moved Permanently</title></head> <body bgcolor="white"> <center><h1>301 Moved Permanently</h1></center> <hr><center>nginx</center> </body> </html>
-v 参数可以显示一次 http 通信的整个过程，包括端口连接和 http request 头信息。
$ curl -v www.kkpan.com * Rebuilt URL to: www.kkpan.com/ * Hostname was NOT found in DNS cache * Trying 202.108.33.60... * Connected to www.kkpan.com (202.108.33.60) port 80 (#0) > GET / HTTP/1.1 > User-Agent: curl/7.35.0 > Host: www.kkpan.com > Accept: */* > < HTTP/1.1 301 Moved Permanently * Server nginx is not blacklisted < Server: nginx < Date: Tue, 23 Aug 2016 08:48:14 GMT < Content-Type: text/html < Location: http://www.kkpan.com.cn/ < Expires: Tue, 23 Aug 2016 08:50:14 GMT < Cache-Control: max-age=120 < Age: 40 < Content-Length: 178 < X-Cache: HIT from xd33-81.kkpan.com.cn < <html> <head><title>301 Moved Permanently</title></head> <body bgcolor="white"> <center><h1>301 Moved Permanently</h1></center> <hr><center>nginx</center> </body> </html> * Connection #0 to host www.kkpan.com left intact
如果觉得上面的信息还不够，那么下面的命令可以查看更详细的通信过程。
$ curl --trace output.txt www.kkpan.com
或者
$ curl --trace-ascii output.txt www.kkpan.com
运行后，打开 output.txt 文件查看。
$ curl --help Usage: curl [options...] <url> Options: (H) means HTTP/HTTPS only, (F) means FTP only --anyauth Pick "any" authentication method (H) -a, --append Append to target file when uploading (F/SFTP) --basic Use HTTP Basic Authentication (H) --cacert FILE CA certificate to verify peer against (SSL) --capath DIR CA directory to verify peer against (SSL) -E, --cert CERT[:PASSWD] Client certificate file and password (SSL) --cert-type TYPE Certificate file type (DER/PEM/ENG) (SSL) --ciphers LIST SSL ciphers to use (SSL) --compressed Request compressed response (using deflate or gzip) -K, --config FILE Specify which config file to read --connect-timeout SECONDS Maximum time allowed for connection -C, --continue-at OFFSET Resumed transfer offset -b, --cookie STRING/FILE String or file to read cookies from (H) -c, --cookie-jar FILE Write cookies to this file after operation (H) --create-dirs Create necessary local directory hierarchy --crlf Convert LF to CRLF in upload --crlfile FILE Get a CRL list in PEM format from the given file -d, --data DATA HTTP POST data (H) --data-ascii DATA HTTP POST ASCII data (H) --data-binary DATA HTTP POST binary data (H) --data-urlencode DATA HTTP POST data url encoded (H) --delegation STRING GSS-API delegation permission --digest Use HTTP Digest Authentication (H) --disable-eprt Inhibit using EPRT or LPRT (F) --disable-epsv Inhibit using EPSV (F) --dns-servers DNS server addrs to use: 1.1.1.1;2.2.2.2 --dns-interface Interface to use for DNS requests --dns-ipv4-addr IPv4 address to use for DNS requests, dot notation --dns-ipv6-addr IPv6 address to use for DNS requests, dot notation -D, --dump-header FILE Write the headers to this file --egd-file FILE EGD socket path for random data (SSL) --engine ENGINE Crypto engine (SSL). "--engine list" for list -f, --fail Fail silently (no output at all) on HTTP errors (H) -F, --form CONTENT Specify HTTP multipart POST data (H) --form-string STRING Specify HTTP multipart POST data (H) --ftp-account DATA Account data string (F) --ftp-alternative-to-user COMMAND String to replace "USER [name]" (F) --ftp-create-dirs Create the remote dirs if not present (F) --ftp-method [MULTICWD/NOCWD/SINGLECWD] Control CWD usage (F) --ftp-pasv Use PASV/EPSV instead of PORT (F) -P, --ftp-port ADR Use PORT with given address instead of PASV (F) --ftp-skip-pasv-ip Skip the IP address for PASV (F) --ftp-pret Send PRET before PASV (for drftpd) (F) --ftp-ssl-ccc Send CCC after authenticating (F) --ftp-ssl-ccc-mode ACTIVE/PASSIVE Set CCC mode (F) --ftp-ssl-control Require SSL/TLS for ftp login, clear for transfer (F) -G, --get Send the -d data with a HTTP GET (H) -g, --globoff Disable URL sequences and ranges using {} and [] -H, --header LINE Custom header to pass to server (H) -I, --head Show document info only -h, --help This help text --hostpubmd5 MD5 Hex encoded MD5 string of the host public key. (SSH) -0, --http1.0 Use HTTP 1.0 (H) --http1.1 Use HTTP 1.1 (H) --http2.0 Use HTTP 2.0 (H) --ignore-content-length Ignore the HTTP Content-Length header -i, --include Include protocol headers in the output (H/F) -k, --insecure Allow connections to SSL sites without certs (H) --interface INTERFACE Specify network interface/address to use -4, --ipv4 Resolve name to IPv4 address -6, --ipv6 Resolve name to IPv6 address -j, --junk-session-cookies Ignore session cookies read from file (H) --keepalive-time SECONDS Interval between keepalive probes --key KEY Private key file name (SSL/SSH) --key-type TYPE Private key file type (DER/PEM/ENG) (SSL) --krb LEVEL Enable Kerberos with specified security level (F) --libcurl FILE Dump libcurl equivalent code of this command line --limit-rate RATE Limit transfer speed to this rate -l, --list-only List only mode (F/POP3) --local-port RANGE Force use of these local port numbers -L, --location Follow redirects (H) --location-trusted like --location and send auth to other hosts (H) -M, --manual Display the full manual --mail-from FROM Mail from this address (SMTP) --mail-rcpt TO Mail to this/these addresses (SMTP) --mail-auth AUTH Originator address of the original email (SMTP) --max-filesize BYTES Maximum file size to download (H/F) --max-redirs NUM Maximum number of redirects allowed (H) -m, --max-time SECONDS Maximum time allowed for the transfer --metalink Process given URLs as metalink XML file --negotiate Use HTTP Negotiate Authentication (H) -n, --netrc Must read .netrc for user name and password --netrc-optional Use either .netrc or URL; overrides -n --netrc-file FILE Set up the netrc filename to use -N, --no-buffer Disable buffering of the output stream --no-keepalive Disable keepalive use on the connection --no-sessionid Disable SSL session-ID reusing (SSL) --noproxy List of hosts which do not use proxy --ntlm Use HTTP NTLM authentication (H) --oauth2-bearer TOKEN OAuth 2 Bearer Token (IMAP, POP3, SMTP) -o, --output FILE Write output to <file> instead of stdout --pass PASS Pass phrase for the private key (SSL/SSH) --post301 Do not switch to GET after following a 301 redirect (H) --post302 Do not switch to GET after following a 302 redirect (H) --post303 Do not switch to GET after following a 303 redirect (H) -#, --progress-bar Display transfer progress as a progress bar --proto PROTOCOLS Enable/disable specified protocols --proto-redir PROTOCOLS Enable/disable specified protocols on redirect -x, --proxy [PROTOCOL://]HOST[:PORT] Use proxy on given port --proxy-anyauth Pick "any" proxy authentication method (H) --proxy-basic Use Basic authentication on the proxy (H) --proxy-digest Use Digest authentication on the proxy (H) --proxy-negotiate Use Negotiate authentication on the proxy (H) --proxy-ntlm Use NTLM authentication on the proxy (H) -U, --proxy-user USER[:PASSWORD] Proxy user and password --proxy1.0 HOST[:PORT] Use HTTP/1.0 proxy on given port -p, --proxytunnel Operate through a HTTP proxy tunnel (using CONNECT) --pubkey KEY Public key file name (SSH) -Q, --quote CMD Send command(s) to server before transfer (F/SFTP) --random-file FILE File for reading random data from (SSL) -r, --range RANGE Retrieve only the bytes within a range --raw Do HTTP "raw", without any transfer decoding (H) -e, --referer Referer URL (H) -J, --remote-header-name Use the header-provided filename (H) -O, --remote-name Write output to a file named as the remote file --remote-name-all Use the remote file name for all URLs -R, --remote-time Set the remote file's time on the local output -X, --request COMMAND Specify request command to use --resolve HOST:PORT:ADDRESS Force resolve of HOST:PORT to ADDRESS --retry NUM Retry request NUM times if transient problems occur --retry-delay SECONDS When retrying, wait this many seconds between each --retry-max-time SECONDS Retry only within this period --sasl-ir Enable initial response in SASL authentication -S, --show-error Show error. With -s, make curl show errors when they occur -s, --silent Silent mode. Don't output anything --socks4 HOST[:PORT] SOCKS4 proxy on given host + port --socks4a HOST[:PORT] SOCKS4a proxy on given host + port --socks5 HOST[:PORT] SOCKS5 proxy on given host + port --socks5-hostname HOST[:PORT] SOCKS5 proxy, pass host name to proxy --socks5-gssapi-service NAME SOCKS5 proxy service name for gssapi --socks5-gssapi-nec Compatibility with NEC SOCKS5 server -Y, --speed-limit RATE Stop transfers below speed-limit for 'speed-time' secs -y, --speed-time SECONDS Time for trig speed-limit abort. Defaults to 30 --ssl Try SSL/TLS (FTP, IMAP, POP3, SMTP) --ssl-reqd Require SSL/TLS (FTP, IMAP, POP3, SMTP) -2, --sslv2 Use SSLv2 (SSL) -3, --sslv3 Use SSLv3 (SSL) --ssl-allow-beast Allow security flaw to improve interop (SSL) --stderr FILE Where to redirect stderr. - means stdout --tcp-nodelay Use the TCP_NODELAY option -t, --telnet-option OPT=VAL Set telnet option --tftp-blksize VALUE Set TFTP BLKSIZE option (must be >512) -z, --time-cond TIME Transfer based on a time condition -1, --tlsv1 Use TLSv1 (SSL) --trace FILE Write a debug trace to the given file --trace-ascii FILE Like --trace but without the hex output --trace-time Add time stamps to trace/verbose output --tr-encoding Request compressed transfer encoding (H) -T, --upload-file FILE Transfer FILE to destination --url URL URL to work with -B, --use-ascii Use ASCII/text transfer -u, --user USER[:PASSWORD][;OPTIONS] Server user, password and login options --tlsuser USER TLS username --tlspassword STRING TLS password --tlsauthtype STRING TLS authentication type (default SRP) -A, --user-agent STRING User-Agent to send to server (H) -v, --verbose Make the operation more talkative -V, --version Show version number and quit -w, --write-out FORMAT What to output after completion --xattr Store metadata in extended file attributes -q If used as the first parameter disables .curlrc
223.5.5.5出现curl: (6) Could not resolve host
![极品五笔输入法安装步骤和使用方法[附常见问题解决办法]](https://www.kkpan.com/d/upload/image/20190813/kkpan.com_rgc2yb.jpg)
