<< Click to Display Table of Contents >> Navigation:  Robo-FTP User's Guide > Script Programming > Script Commands > All Script Commands > FTPGETDIFF         Get specific changes within FTP site file system

 

 

The FTPDIFF and FTPGETDIFF commands work together to identify and process changes to files on a remote server.

 

The FTPGETDIFF command sets the values of seven internal variables with details describing a change to a single file on a remote site. These details are pulled from a snapshot database where they were inserted by a previous call to the FTPDIFF command. Subsequent calls to FTPGETDIFF fetch the details of subsequent changes from the database. The FTPGETDIFF command is typically used in a loop so that each detected change is processed during one iteration of the loop. Depending on your needs, the processing may involve one or more of the internal variables set by this command. It is possible for FTPGETDIFF to report file changes in alphabetical order rather than folder hierarchical order depending on how the records are stored in the snapshot database. This command returns $ERROR_READ_EOF when there are no more differences in the database. The FTPDIFFREWIND command is available to reset the file pointer to the first change recorded in the database.

 

If the [ dbfile ] argument is omitted, the default file name “snapshot_site.sql” file is used. An error occurs if the snapshot database file does not exist.

 

The FTPGETDIFF command sets the values of the following variables that you can use in your script logic:

 

 

The possible values of %ftpdifffileid and %ftpdifffiletext are:

 

 

To monitor only for specific type(s) of changes, use the /difftype option. To monitor for multiple types of changes, you can either use the /difftype option multiple times (for example, /difftype=$DIFF_FILE_SIZE /difftype=$DIFF_FILE_DATETIME) or separate the values with a pipe character (for example, /difftype=$DIFF_FILE_SIZE|$DIFF_FILE_DATETIME).

 

Here is a simple example that shows how FTPGETDIFF might be used inside a loop to write a text file that lists all the changes found by FTPDIFF:

 

FTPDIFF "*"

:loop

FTPGETDIFF

IFERROR= $ERROR_READ_EOF GOTO done

SET change = "File: " + %ftpdifffilepath + " " + %ftpdifffiletext

WRITEFILE "differences.txt" change /append

GOTO loop

:done

 

The following example loops through all changes and downloads only the new files from a remote site:

 

FTPDIFF "*"

:loop

FTPGETDIFF

IFERROR= $ERROR_READ_EOF GOTO done

IFNUM!= %ftpdifffileid $DIFF_FILE_IS_NEW GOTO loop

RCVFILE %ftpdifffilename

GOTO loop

:done

 

Sometimes it is helpful to start with a fresh database instead of persisting it across runs of a script. This can be achieved by simply preemptively deleting the snapshot database file before calling FTPDIFF. Using this technique allows you to process all files in a directory in a very efficient manner. The following example illustrates how this can be done:

 

SET dbpath = "C:\path\to\database.sql"

DELETE dbpath      ;; preemptively delete dbpath in case it already exists so

                  ;;  so that the database effectively does not persist across runs

FTPDIFF "*" dbpath

:loop

FTPGETDIFF dbpath

IFERROR= $ERROR_READ_EOF GOTO done    

;; process files here:

SET msg = "File " + %ftpdifffilepath + " has size " + %ftpdiffsize + " and was last modified " + %ftpdiffdatetime

CONSOLEMSG msg

GOTO loop

:done

 

 

If you need to restart the loop, use the FTPDIFFREWIND command to reset the file pointer to the first difference recorded in the snapshot database.

 

Normally, all current differences are marked "done" when FTPDIFF is called again. The /commitlast option increases fault tolerance by causing FTPGETDIFF to mark the previously retrieved difference done. This way, a difference should not be processed twice if loop processing is interrupted after FTPGETDIFF is called but before the full loop iteration is complete.

 

Note: Snapshot database files are small SQLite database files created by Robo-FTP to support the DIFF and FTPDIFF family of script commands.

 

Special value unset

 

The /smallerthan=xx, /largerthan=xx, /olderthan=xx, and /newerthan=xx options also accept a special value "unset". When provided, that corresponding option will be effectively disabled. This allows each option to be turned on or off selectively depending on the values of passed in variables. Consider the following usage:

 

 SET upperlimit = "unset" ;; ensure that /smallerthan option is turned off

 SET lowerlimit = 1024

 FTPGETDIFF /smallerthan=upperlimit /largerthan=lowerlimit

 

Important

The success of this command depends on Robo-FTP's ability to automatically read and understand the directory listings returned by the remote site. Most HTTP/HTTPS sites do not return listings in a supported format and many return no raw directory listings in response to HTTP GET requests based on slash-terminated URLs. Some servers respond to HEAD requests and are partially compatible. Some supported HTTP listing types like APACHE_DEFAULT include file sizes rounded to the nearest megabyte or kilobyte and are therefore not fully compatible with this command. Contact technical support if you have an urgent need related to a raw directory listing format that is currently unsupported.

 

 

Related command(s): FTPDIFF, FTPDIFFREWIND, GETDIFF

See also: Processing Dynamic Folders, Using the built-in database engine, Alternate Default Path