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Chapter 6: Using PSFTP to transfer files securely

PSFTP, the PuTTY SFTP client, is a tool for transferring files securely between computers using an SSH connection.

PSFTP differs from PSCP in the following ways:

6.1 Starting PSFTP

The usual way to start PSFTP is from a command prompt, much like PSCP. To do this, it will need either to be on your PATH or in your current directory. To add the directory containing PSFTP to your PATH environment variable, type into the console window: 

set PATH=C:\path\to\putty\directory;%PATH%

Unlike PSCP, however, PSFTP has no complex command-line syntax; you just specify a host name and perhaps a user name: 

psftp server.example.com

or perhaps 

psftp [email protected]

Alternatively, if you just type psftp on its own (or double-click the PSFTP icon in the Windows GUI), you will see the PSFTP prompt, and a message telling you PSFTP has not connected to any server: 

C:\>psftp
psftp: no hostname specified; use "open host.name" to connect
psftp>

At this point you can type open server.example.com or open [email protected] to start a session.

PSFTP accepts all the general command line options supported by the PuTTY tools, except the ones which make no sense in a file transfer utility. See section 3.11.3 for a description of these options. (The ones not supported by PSFTP are clearly marked.)

PSFTP also supports some of its own options. The following sections describe PSFTP's specific command-line options.

6.1.1 -b: specify a file containing batch commands

In normal operation, PSFTP is an interactive program which displays a command line and accepts commands from the keyboard.

If you need to do automated tasks with PSFTP, you would probably prefer to specify a set of commands in advance and have them executed automatically. The -b option allows you to do this. You use it with a file name containing batch commands. For example, you might create a file called myscript.scr containing lines like this: 

cd /home/ftp/users/jeff
del jam-old.tar.gz
ren jam.tar.gz jam-old.tar.gz
put jam.tar.gz
chmod a+r jam.tar.gz

and then you could run the script by typing 

psftp user@hostname -b myscript.scr

When you run a batch script in this way, PSFTP will abort the script if any command fails to complete successfully. To change this behaviour, you can add the -be option (section 6.1.3).

PSFTP will terminate after it finishes executing the batch script.

6.1.2 -bc: display batch commands as they are run

The -bc option alters what PSFTP displays while processing a batch script specified with -b. With the -bc option, PSFTP will display prompts and commands just as if the commands had been typed at the keyboard. So instead of seeing this: 

C:\>psftp fred@hostname -b batchfile
Sent username "fred"
Remote working directory is /home/fred
Listing directory /home/fred/lib
drwxrwsr-x    4 fred     fred         1024 Sep  6 10:42 .
drwxr-sr-x   25 fred     fred         2048 Dec 14 09:36 ..
drwxrwsr-x    3 fred     fred         1024 Apr 17  2000 jed
lrwxrwxrwx    1 fred     fred           24 Apr 17  2000 timber
drwxrwsr-x    2 fred     fred         1024 Mar 13  2000 trn

you might see this: 

C:\>psftp fred@hostname -bc -b batchfile
Sent username "fred"
Remote working directory is /home/fred
psftp> dir lib
Listing directory /home/fred/lib
drwxrwsr-x    4 fred     fred         1024 Sep  6 10:42 .
drwxr-sr-x   25 fred     fred         2048 Dec 14 09:36 ..
drwxrwsr-x    3 fred     fred         1024 Apr 17  2000 jed
lrwxrwxrwx    1 fred     fred           24 Apr 17  2000 timber
drwxrwsr-x    2 fred     fred         1024 Mar 13  2000 trn
psftp> quit

6.1.3 -be: continue batch processing on errors

When running a batch file, this additional option causes PSFTP to continue processing even if a command fails to complete successfully.

You might want this to happen if you wanted to delete a file and didn't care if it was already not present, for example.

6.1.4 -batch: avoid interactive prompts

If you use the -batch option, PSFTP will never give an interactive prompt while establishing the connection. If the server's host key is invalid, for example (see section 2.2), then the connection will simply be abandoned instead of asking you what to do next.

This may help PSFTP's behaviour when it is used in automated scripts: using -batch, if something goes wrong at connection time, the batch job will fail rather than hang.

6.1.4.1 -no-sanitise-stderr: control error message sanitisation

The -no-sanitise-stderr option will cause PSFTP to pass through the server's standard-error stream literally, without stripping control characters from it first. This might be useful if the server were sending coloured error messages, but it also gives the server the ability to have unexpected effects on your terminal display. For more discussion, see section 7.2.3.5.

6.2 Running PSFTP

Once you have started your PSFTP session, you will see a psftp> prompt. You can now type commands to perform file-transfer functions. This section lists all the available commands.

Any line starting with a # will be treated as a comment and ignored.

6.2.1 General quoting rules for PSFTP commands

Most PSFTP commands are considered by the PSFTP command interpreter as a sequence of words, separated by spaces. For example, the command ren oldfilename newfilename splits up into three words: ren (the command name), oldfilename (the name of the file to be renamed), and newfilename (the new name to give the file).

Sometimes you will need to specify file names that contain spaces. In order to do this, you can surround the file name with double quotes. This works equally well for local file names and remote file names: 

psftp> get "spacey file name.txt" "save it under this name.txt"

The double quotes themselves will not appear as part of the file names; they are removed by PSFTP and their only effect is to stop the spaces inside them from acting as word separators.

If you need to use a double quote (on some types of remote system, such as Unix, you are allowed to use double quotes in file names), you can do this by doubling it. This works both inside and outside double quotes. For example, this command 

psftp> ren ""this"" "a file with ""quotes"" in it"

will take a file whose current name is "this" (with a double quote character at the beginning and the end) and rename it to a file whose name is a file with "quotes" in it.

(The one exception to the PSFTP quoting rules is the ! command, which passes its command line straight to Windows without splitting it up into words at all. See section 6.2.19.)

6.2.2 Wildcards in PSFTP

Several commands in PSFTP support ‘wildcards’ to select multiple files.

For local file specifications (such as the first argument to put), wildcard rules for the local operating system are used. For instance, PSFTP running on Windows might require the use of *.* where PSFTP on Unix would need *.

For remote file specifications (such as the first argument to get), PSFTP uses a standard wildcard syntax (similar to POSIX wildcards):

A leading period (.) on a filename is not treated specially, unlike in some Unix contexts; get * will fetch all files, whether or not they start with a leading period.

6.2.3 The open command: start a session

If you started PSFTP by double-clicking in the GUI, or just by typing psftp at the command line, you will need to open a connection to an SFTP server before you can issue any other commands (except help and quit).

To create a connection, type open host.name, or if you need to specify a user name as well you can type open [email protected]. You can optionally specify a port as well: open [email protected] 22.

Once you have issued this command, you will not be able to issue it again, even if the command fails (for example, if you mistype the host name or the connection times out). So if the connection is not opened successfully, PSFTP will terminate immediately.

6.2.4 The quit command: end your session

When you have finished your session, type the command quit to close the connection, terminate PSFTP and return to the command line (or just close the PSFTP console window if you started it from the GUI).

You can also use the bye and exit commands, which have exactly the same effect.

6.2.5 The close command: close your connection

If you just want to close the network connection but keep PSFTP running, you can use the close command. You can then use the open command to open a new connection.

6.2.6 The help command: get quick online help

If you type help, PSFTP will give a short list of the available commands.

If you type help with a command name - for example, help get - then PSFTP will give a short piece of help on that particular command.

6.2.7 The cd and pwd commands: changing the remote working directory

PSFTP maintains a notion of your ‘working directory’ on the server. This is the default directory that other commands will operate on. For example, if you type get filename.dat then PSFTP will look for filename.dat in your remote working directory on the server.

To change your remote working directory, use the cd command. If you don't provide an argument, cd will return you to your home directory on the server (more precisely, the remote directory you were in at the start of the connection).

To display your current remote working directory, type pwd.

6.2.8 The lcd and lpwd commands: changing the local working directory

As well as having a working directory on the remote server, PSFTP also has a working directory on your local machine (just like any other Windows process). This is the default local directory that other commands will operate on. For example, if you type get filename.dat then PSFTP will save the resulting file as filename.dat in your local working directory.

To change your local working directory, use the lcd command. To display your current local working directory, type lpwd.

6.2.9 The get command: fetch a file from the server

To download a file from the server and store it on your local PC, you use the get command.

In its simplest form, you just use this with a file name: 

get myfile.dat

If you want to store the file locally under a different name, specify the local file name after the remote one: 

get myfile.dat newname.dat

This will fetch the file on the server called myfile.dat, but will save it to your local machine under the name newname.dat.

To fetch an entire directory recursively, you can use the -r option: 

get -r mydir
get -r mydir newname

(If you want to fetch a file whose name starts with a hyphen, you may have to use the -- special argument, which stops get from interpreting anything as a switch after it. For example, ‘get -- -silly-name-’.)

6.2.10 The put command: send a file to the server

To upload a file to the server from your local PC, you use the put command.

In its simplest form, you just use this with a file name: 

put myfile.dat

If you want to store the file remotely under a different name, specify the remote file name after the local one: 

put myfile.dat newname.dat

This will send the local file called myfile.dat, but will store it on the server under the name newname.dat.

To send an entire directory recursively, you can use the -r option: 

put -r mydir
put -r mydir newname

(If you want to send a file whose name starts with a hyphen, you may have to use the -- special argument, which stops put from interpreting anything as a switch after it. For example, ‘put -- -silly-name-’.)

6.2.11 The mget and mput commands: fetch or send multiple files

mget works almost exactly like get, except that it allows you to specify more than one file to fetch at once. You can do this in two ways:

Every argument to mget is treated as the name of a file to fetch (unlike get, which will interpret at most one argument like that, and a second argument will be treated as an alternative name under which to store the retrieved file), or a wildcard expression matching more than one file.

The -r and -- options from get are also available with mget.

mput is similar to put, with the same differences.

6.2.12 The reget and reput commands: resuming file transfers

If a file transfer fails half way through, and you end up with half the file stored on your disk, you can resume the file transfer using the reget and reput commands. These work exactly like the get and put commands, but they check for the presence of the half-written destination file and start transferring from where the last attempt left off.

The syntax of reget and reput is exactly the same as the syntax of get and put: 

reget myfile.dat
reget myfile.dat newname.dat
reget -r mydir

These commands are intended mainly for resuming interrupted transfers. They assume that the remote file or directory structure has not changed in any way; if there have been changes, you may end up with corrupted files. In particular, the -r option will not pick up changes to files or directories already transferred in full.

6.2.13 The dir command: list remote files

To list the files in your remote working directory, just type dir.

You can also list the contents of a different directory by typing dir followed by the directory name: 

dir /home/fred
dir sources

And you can list a subset of the contents of a directory by providing a wildcard: 

dir /home/fred/*.txt
dir sources/*.c

The ls command works exactly the same way as dir.

6.2.14 The chmod command: change permissions on remote files

PSFTP allows you to modify the file permissions on files and directories on the server. You do this using the chmod command, which works very much like the Unix chmod command.

The basic syntax is chmod modes file, where modes represents a modification to the file permissions, and file is the filename to modify. You can specify multiple files or wildcards. For example: 

chmod go-rwx,u+w privatefile
chmod a+r public*
chmod 640 groupfile1 groupfile2

The modes parameter can be a set of octal digits in the Unix style. (If you don't know what this means, you probably don't want to be using it!) Alternatively, it can be a list of permission modifications, separated by commas. Each modification consists of:

So the above examples would do:

In addition to all this, there are a few extra special cases for Unix systems. On non-Unix systems these are unlikely to be useful:

6.2.15 The del command: delete remote files

To delete a file on the server, type del and then the filename or filenames: 

del oldfile.dat
del file1.txt file2.txt
del *.o

Files will be deleted without further prompting, even if multiple files are specified.

del will only delete files. You cannot use it to delete directories; use rmdir for that.

The rm command works exactly the same way as del.

6.2.16 The mkdir command: create remote directories

To create a directory on the server, type mkdir and then the directory name: 

mkdir newstuff

You can specify multiple directories to create at once: 

mkdir dir1 dir2 dir3

6.2.17 The rmdir command: remove remote directories

To remove a directory on the server, type rmdir and then the directory name or names: 

rmdir oldstuff
rmdir *.old ancient

Directories will be deleted without further prompting, even if multiple directories are specified.

Most SFTP servers will probably refuse to remove a directory if the directory has anything in it, so you will need to delete the contents first.

6.2.18 The mv command: move and rename remote files

To rename a single file on the server, type mv, then the current file name, and then the new file name: 

mv oldfile newname

You can also move the file into a different directory and change the name: 

mv oldfile dir/newname

To move one or more files into an existing subdirectory, specify the files (using wildcards if desired), and then the destination directory: 

mv file dir
mv file1 dir1/file2 dir2
mv *.c *.h ..

The rename and ren commands work exactly the same way as mv.

6.2.19 The ! command: run a local Windows command

You can run local Windows commands using the ! command. This is the only PSFTP command that is not subject to the command quoting rules given in section 6.2.1. If any command line begins with the ! character, then the rest of the line will be passed straight to Windows without further translation.

For example, if you want to move an existing copy of a file out of the way before downloading an updated version, you might type: 

psftp> !ren myfile.dat myfile.bak
psftp> get myfile.dat

using the Windows ren command to rename files on your local PC.

6.3 Using public key authentication with PSFTP

Like PuTTY, PSFTP can authenticate using a public key instead of a password. There are three ways you can do this.

Firstly, PSFTP can use PuTTY saved sessions in place of hostnames. So you might do this:

Secondly, you can supply the name of a private key file on the command line, with the -i option. See section 3.11.3.18 for more information.

Thirdly, PSFTP will attempt to authenticate using Pageant if Pageant is running (see chapter 9). So you would do this:

For more general information on public-key authentication, see chapter 8.

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[PuTTY release 0.75]