curlでヘッダ情報やHTTPステータスコードのみを出力する方法

`curl`コマンドでAPIリクエストを投げる際、ヘッダ情報を出力するオプションを忘れがちなのでメモ。ついでにHTTPステータスコードのみを出力させる方法も調べてみた。

# レスポンスボディのみを取得する場合

`curl`で何もオプションを付けずに対象URLを渡すだけだと、レスポンスボディのみが出力される。

```terminal
$ curl "http://geoapi.heartrails.com/api/json?method=searchByPostal&postal=1010047"
```

```terminal
{
  "response": {
    "location": [
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田一丁目",
        "town_kana": "うちかんだ1ちょうめ",
        "x": "139.765943",
        "y": "35.690701",
        "prefecture": "東京都",
        "postal": "1010047"
      },
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田二丁目",
        "town_kana": "うちかんだ2ちょうめ",
        "x": "139.768192",
        "y": "35.690854",
        "prefecture": "東京都",
        "postal": "1010047"
      },
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田三丁目",
        "town_kana": "うちかんだ3ちょうめ",
        "x": "139.769899",
        "y": "35.691568",
        "prefecture": "東京都",
        "postal": "1010047"
      }
    ]
  }
}
```

# ステータスラインとレスポンスヘッダのみを取得する場合

コマンドオプションとして大文字の`I`(head)を指定すると、ヘッダ情報（ステータスラインとレスポンスヘッダ）が出力される。

```terminal
$ curl -I "http://geoapi.heartrails.com/api/json?method=searchByPostal&postal=1010047"
```

```terminal
HTTP/1.1 200 OK
Date: Sat, 22 Feb 2020 08:25:04 GMT
Content-Type: application/json; charset=utf-8
Connection: keep-alive
Server: nginx
ETag: "e287c729017cc9785487098b6b103af6"
Cache-Control: max-age=0, private, must-revalidate
X-UA-Compatible: IE=Edge,chrome=1
X-Runtime: 0.003712
```


`-I, --head          Show document info only` の `info`部分をとって`I`なのかな？

# すべてのレスポンスメッセージを取得する場合

コマンドオプションとして小文字の`i`(include)を指定すると、ヘッダ情報（ステータスラインとレスポンスヘッダ）とレスポンスボディの両方が出力される。

```terminal
$ curl -i "http://geoapi.heartrails.com/api/json?method=searchByPostal&postal=1010047"
```

```terminal
HTTP/1.1 200 OK
Date: Sat, 22 Feb 2020 08:27:51 GMT
Content-Type: application/json; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
Server: nginx
ETag: "e287c729017cc9785487098b6b103af6"
Cache-Control: max-age=0, private, must-revalidate
X-UA-Compatible: IE=Edge,chrome=1
X-Runtime: 0.003450

{
  "response": {
    "location": [
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田一丁目",
        "town_kana": "うちかんだ1ちょうめ",
        "x": "139.765943",
        "y": "35.690701",
        "prefecture": "東京都",
        "postal": "1010047"
      },
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田二丁目",
        "town_kana": "うちかんだ2ちょうめ",
        "x": "139.768192",
        "y": "35.690854",
        "prefecture": "東京都",
        "postal": "1010047"
      },
      {
        "city": "千代田区",
        "city_kana": "ちよだく",
        "town": "内神田三丁目",
        "town_kana": "うちかんだ3ちょうめ",
        "x": "139.769899",
        "y": "35.691568",
        "prefecture": "東京都",
        "postal": "1010047"
      }
    ]
  }
}
```

# ステータスコードのみを取得する場合
ステータスコードのみを出力させるには、`o`オプションと、`w`オプションの組み合わせで可能。

```terminal
$ curl "http://geoapi.heartrails.com/api/json?method=searchByPostal&postal=1010047" -o /dev/null -w '%{http_code}\n' -s
```

```terminal
200
```

- `o`オプション(output FILE)は、本来実行結果をファイルへ出力させられるもの。ここでは`/dev/null`という次元の彼方へ飛ばしている。
- `w`オプション(write-out)で`http_code`を指定。
- `s`オプション(silent)をつけると、進捗状況やエラーなどの余計な出力を非表示にすることができる。エラーは表示したいという場合は、大文字の`S`(show-error)を付けて`-sS`とすれば良い。


# その他のオプション

`h`オプション(help)で`curl`コマンドのヘルプが参照できる。

```terminal
$ curl -h
```

```terminal
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-status   Verify the status of the server certificate (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   Read config from FILE
     --connect-timeout SECONDS  Maximum time allowed for connection
     --connect-to HOST1:PORT1:HOST2:PORT2 Connect to host (network level)
 -C, --continue-at OFFSET  Resumed transfer OFFSET
 -b, --cookie STRING/FILE  Read cookies from STRING/FILE (H)
 -c, --cookie-jar FILE  Write cookies to 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-raw DATA  HTTP POST data, '@' allowed (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 received headers to FILE
     --egd-file FILE  EGD socket path for random data (SSL)
     --engine ENGINE  Crypto engine (use "--engine list" for list) (SSL)
     --expect100-timeout SECONDS How long to wait for 100-continue (H)
 -f, --fail          Fail silently (no output at all) on HTTP errors (H)
     --fail-early    Fail on first transfer error, do not continue
     --false-start   Enable TLS False Start.
 -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   Pass custom header LINE 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         Use HTTP 2 (H)
     --http2-prior-knowledge  Use HTTP 2 without HTTP/1.1 Upgrade (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  Use network INTERFACE (or address)
 -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  Wait SECONDS 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 security LEVEL (F)
     --libcurl FILE  Dump libcurl equivalent code of this command line
     --limit-rate RATE  Limit transfer speed to RATE
 -l, --list-only     List only mode (F/POP3)
     --local-port RANGE  Force use of RANGE for local port numbers
 -L, --location      Follow redirects (H)
     --location-trusted  Like '--location', and send auth to other hosts (H)
     --login-options OPTIONS  Server login options (IMAP, POP3, SMTP)
 -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 (SPNEGO) authentication (H)
 -n, --netrc         Must read .netrc for user name and password
     --netrc-optional  Use either .netrc or URL; overrides -n
     --netrc-file FILE  Specify FILE for netrc
 -:, --next          Allows the following URL to use a separate set of options
     --no-alpn       Disable the ALPN TLS extension (H)
 -N, --no-buffer     Disable buffering of the output stream
     --no-keepalive  Disable keepalive use on the connection
     --no-npn        Disable the NPN TLS extension (H)
     --no-sessionid  Disable SSL session-ID reusing (SSL)
     --noproxy       List of hosts which do not use proxy
     --ntlm          Use HTTP NTLM authentication (H)
     --ntlm-wb       Use HTTP NTLM authentication with winbind (H)
     --oauth2-bearer TOKEN  OAuth 2 Bearer Token (IMAP, POP3, SMTP)
 -o, --output FILE   Write to FILE instead of stdout
     --pass PASS     Pass phrase for the private key (SSL/SSH)
     --path-as-is    Do not squash .. sequences in URL path
     --pinnedpubkey FILE/HASHES Public key to verify peer against (SSL)
     --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)
     --preproxy [PROTOCOL://]HOST[:PORT] Proxy before HTTP(S) proxy
 -#, --progress-bar  Display transfer progress as a progress bar
     --proto PROTOCOLS  Enable/disable PROTOCOLS
     --proto-default PROTOCOL  Use PROTOCOL for any URL missing a scheme
     --proto-redir PROTOCOLS   Enable/disable 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-cacert FILE CA certificate to verify peer against for proxy (SSL)
     --proxy-capath DIR CA directory to verify peer against for proxy (SSL)
     --proxy-cert CERT[:PASSWD] Client certificate file and password for proxy (SSL)
     --proxy-cert-type TYPE Certificate file type (DER/PEM/ENG) for proxy (SSL)
     --proxy-ciphers LIST SSL ciphers to use for proxy (SSL)
     --proxy-crlfile FILE Get a CRL list in PEM format from the given file for proxy
     --proxy-insecure Allow connections to SSL sites without certs for proxy (H)
     --proxy-key KEY Private key file name for proxy (SSL)
     --proxy-key-type TYPE Private key file type for proxy (DER/PEM/ENG) (SSL)
     --proxy-negotiate  Use HTTP Negotiate (SPNEGO) authentication on the proxy (H)
     --proxy-ntlm    Use NTLM authentication on the proxy (H)
     --proxy-header LINE Pass custom header LINE to proxy (H)
     --proxy-pass PASS Pass phrase for the private key for proxy (SSL)
     --proxy-ssl-allow-beast Allow security flaw to improve interop for proxy (SSL)
     --proxy-tlsv1   Use TLSv1 for proxy (SSL)
     --proxy-tlsuser USER TLS username for proxy
     --proxy-tlspassword STRING TLS password for proxy
     --proxy-tlsauthtype STRING TLS authentication type for proxy (default SRP)
     --proxy-service-name NAME  SPNEGO proxy service name
     --service-name NAME  SPNEGO service name
 -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 RANGE
     --raw           Do HTTP "raw"; no 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-connrefused  Retry on connection refused (use with --retry)
     --retry-delay SECONDS  Wait SECONDS between retries
     --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 GSS-API
     --socks5-gssapi-nec  Compatibility with NEC SOCKS5 server
 -Y, --speed-limit RATE  Stop transfers below RATE for 'speed-time' secs
 -y, --speed-time SECONDS  Trigger 'speed-limit' abort after SECONDS (default: 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)
     --ssl-no-revoke    Disable cert revocation checks (WinSSL)
     --stderr FILE   Where to redirect stderr (use "-" for stdout)
     --suppress-connect-headers  Suppress proxy CONNECT response headers
     --tcp-nodelay   Use the TCP_NODELAY option
     --tcp-fastopen  Use TCP Fast Open
 -t, --telnet-option OPT=VAL  Set telnet option
     --tftp-blksize VALUE  Set TFTP BLKSIZE option (must be >512)
     --tftp-no-options  Do not send TFTP options requests
 -z, --time-cond TIME   Transfer based on a time condition
 -1, --tlsv1         Use >= TLSv1 (SSL)
     --tlsv1.0       Use TLSv1.0 (SSL)
     --tlsv1.1       Use TLSv1.1 (SSL)
     --tlsv1.2       Use TLSv1.2 (SSL)
     --tlsv1.3       Use TLSv1.3 (SSL)
     --tls-max VERSION  Use TLS up to VERSION (SSL)
     --trace FILE    Write a debug trace to FILE
     --trace-ascii FILE  Like --trace, but without 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]  Server user and password
     --tlsuser USER  TLS username
     --tlspassword STRING  TLS password
     --tlsauthtype STRING  TLS authentication type (default: SRP)
     --unix-socket PATH    Connect through this Unix domain socket
     --abstract-unix-socket PATH Connect to an abstract Unix domain socket
 -A, --user-agent STRING  Send User-Agent STRING to server (H)
 -v, --verbose       Make the operation more talkative
 -V, --version       Show version number and quit
 -w, --write-out FORMAT  Use output FORMAT after completion
     --xattr         Store metadata in extended file attributes
 -q, --disable       Disable .curlrc (must be first parameter)
```

オプション207個もあった。

```terminal
$ curl -h | egrep -- '^[[:space:]]+-' | wc -l
     207
```

# 関連情報
総本山。
[curl](https://curl.se/)

マニュアルはこちら。
[curl - Tutorial](https://curl.haxx.se/docs/manual.html)

ちなみにGitHubリポジトリもある。
[curl/curl: A command line tool and library for transferring data with URL syntax, supporting HTTP, HTTPS, FTP, FTPS, GOPHER, TFTP, SCP, SFTP, SMB, TELNET, DICT, LDAP, LDAPS, FILE, IMAP, SMTP, POP3, RTSP and RTMP. libcurl offers a myriad of powerful features](https://github.com/curl/curl)

日本語レスポンス見るときはjqコマンド使ってる。
[jqコマンドでcurlのJSONレスポンスを見やすくする - Qiita](https://qiita.com/unsoluble_sugar/items/8a1fcbec2d5e336ecbf3)