从FTP服务器检索文件的修改的DateTime [英] Retrieve modified DateTime of a file from an FTP Server
问题描述
是否可以找到R中FTP服务器上文件的修改日期/时间?我找到了列出所有可用文件的好方法,但是我只想下载自上次检查以来已更新的文件.我尝试使用:
Is there a way to find the modified date/time for files on an FTP server in R? I have found a great way to list all of the files that are available, but I only want to download ones that have been updated since my last check. I tried using:
info<-file.info(url)
但是,它返回一个非常丑陋的列表.我的网址由以下内容组成:" ftp://username:password@FTPServer//filepath.xml "
However, it returns a pretty ugly list of nothing. My url is made up of: "ftp://username:password@FTPServer//filepath.xml"
推荐答案
直到我们看到此特定 FTP服务器(它们都是不同的)的FTP输出(用于目录列表),这是您可以遵循的路径:
Until we see the output from this particular FTP server (they are all different) for directory listings, here's a path you can follow:
library(curl)
library(stringr)
获取原始目录列表:
con <- curl("ftp://ftp.FreeBSD.org/pub/FreeBSD/")
dat <- readLines(con)
close(con)
dat
## [1] "-rw-rw-r-- 1 ftp ftp 4259 May 07 16:18 README.TXT"
## [2] "-rw-rw-r-- 1 ftp ftp 35 Sep 09 21:00 TIMESTAMP"
## [3] "drwxrwxr-x 9 ftp ftp 11 Sep 09 21:00 development"
## [4] "-rw-r--r-- 1 ftp ftp 2566 Sep 09 10:00 dir.sizes"
## [5] "drwxrwxr-x 28 ftp ftp 52 Aug 23 10:44 doc"
## [6] "drwxrwxr-x 5 ftp ftp 5 Aug 05 04:16 ports"
## [7] "drwxrwxr-x 10 ftp ftp 12 Sep 09 21:00 releases"
过滤目录:
no_dirs <- grep("^d", dat, value=TRUE, invert=TRUE)
no_dirs
## [1] "-rw-rw-r-- 1 ftp ftp 4259 May 07 16:18 README.TXT"
## [2] "-rw-rw-r-- 1 ftp ftp 35 Sep 09 21:00 TIMESTAMP"
## [3] "-rw-r--r-- 1 ftp ftp 2566 Sep 09 10:00 dir.sizes"
仅提取时间戳和文件名:
Extract just the timestamp and filename:
date_and_name <- sub("^[[:alnum:][:punct:][:blank:]]{43}", "", no_dirs)
date_ane_name
## [1] "May 07 16:18 README.TXT"
## [2] "Sep 09 21:00 TIMESTAMP"
## [3] "Sep 09 10:00 dir.sizes"
将它们放入 data.frame
:
do.call(rbind.data.frame,
lapply(str_match_all(date_and_name, "([[:alnum:] :]{12}) (.*)$"),
function(x) {
data.frame(timestamp=x[2],
filename=x[3],
stringsAsFactors=FALSE)
})) -> dat
dat
## timestamp filename
## 1 May 07 16:18 README.TXT
## 2 Sep 09 21:00 TIMESTAMP
## 3 Sep 09 10:00 dir.sizes
您仍然需要将时间戳转换为 POSIXct
,但这很简单.
You still need to convert the timestamp to a POSIXct
but that's trivial.
此特定示例取决于该系统的FTP目录列表响应.只需为您更改正则表达式即可.
This particular example is dependent on that system's FTP directory listing response. Just change the regexes for yours.
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