Annotation of embedaddon/lrzsz/man/lsz.1, revision 1.1
1.1 ! misho 1: '\"
! 2: '\" Revision Level
! 3: '\" Last Delta 04-21-88
! 4: .TH SZ 1 2.6.1996 lrzsz-0.12b
! 5: .SH NAME
! 6: sx, sb, sz \- XMODEM, YMODEM, ZMODEM file send
! 7: .SH SYNOPSIS
! 8: sz
! 9: .RB [\- +8abdefkLlNnopqTtuvyY ]
! 10: .I file ...
! 11: .br
! 12: sb
! 13: .RB [\- adfkqtuv ]
! 14: .I file ...
! 15: .br
! 16: sx
! 17: .RB [\- akqtuv ]
! 18: .I file
! 19: .br
! 20: sz
! 21: .RB [\- oqtv ]
! 22: .B "-c COMMAND"
! 23: .br
! 24: sz
! 25: .RB [\- oqtv ]
! 26: .B "-i COMMAND"
! 27: .br
! 28: sz -TT
! 29: .SH DESCRIPTION
! 30: .B Sz
! 31: uses the ZMODEM, YMODEM or XMODEM error correcting protocol to send
! 32: one or more files over a dial-in serial port to a variety of programs running under
! 33: PC-DOS, CP/M, Unix, VMS, and other operating systems.
! 34:
! 35: While
! 36: .I rz
! 37: is smart enough to be called from
! 38: .I cu(1),
! 39: very few versions of
! 40: .I cu(1)
! 41: are smart enough to allow
! 42: .I sz
! 43: to work properly.
! 44: Unix flavors of Professional-YAM are available for such dial-out application.
! 45:
! 46:
! 47: .B Sz
! 48: sends one or more files with ZMODEM protocol.
! 49:
! 50: ZMODEM
! 51: greatly simplifies file transfers compared to XMODEM.
! 52: In addition to a friendly user interface, ZMODEM
! 53: provides Personal Computer and other users
! 54: an efficient, accurate, and robust file transfer method.
! 55:
! 56: ZMODEM provides complete
! 57: .B "END-TO-END"
! 58: data integrity between application programs.
! 59: ZMODEM's 32 bit CRC catches errors
! 60: that sneak into even the most advanced networks.
! 61:
! 62: Advanced file management features include
! 63: AutoDownload (Automatic file Download initiated without user intervention),
! 64: Display of individual and total file lengths and transmission time estimates,
! 65: Crash Recovery,
! 66: selective file transfers,
! 67: and preservation of
! 68: exact file date and length.
! 69:
! 70: Output from another program may be piped to
! 71: .B sz
! 72: for transmission by denoting standard input with "-":
! 73: .ce
! 74: ls -l | sz -
! 75: The program output is transmitted with the filename sPID.sz
! 76: where PID is the process ID of the
! 77: .B sz
! 78: program.
! 79: If the environment variable
! 80: .B ONAME
! 81: is set, that is used instead.
! 82: In this case, the Unix command:
! 83: .ce
! 84: ls -l | ONAME=con sz -ay -
! 85: will send a "file" to the PC-DOS console display.
! 86: The
! 87: .B -y
! 88: option instructs the receiver to open the file for writing unconditionally.
! 89: The
! 90: .B -a
! 91: option
! 92: causes the receiver to convert Unix newlines to PC-DOS carriage returns
! 93: and linefeeds.
! 94:
! 95:
! 96: .B Sb
! 97: batch sends one or more files with YMODEM or ZMODEM protocol.
! 98: The initial ZMODEM initialization is not sent.
! 99: When requested by the receiver,
! 100: .B sb
! 101: supports
! 102: .B YMODEM-g
! 103: with "cbreak" tty mode, XON/XOFF flow control,
! 104: and interrupt character set to CAN (^X).
! 105: .B YMODEM-g
! 106: (Professional-YAM
! 107: .B g
! 108: option)
! 109: increases throughput over error free channels
! 110: (direct connection, X.PC, etc.)
! 111: by not acknowledging each transmitted sector.
! 112:
! 113: On
! 114: .SM Unix
! 115: systems, additional information about the file is transmitted.
! 116: If the receiving program uses this information,
! 117: the transmitted file length controls the exact number of bytes written to
! 118: the output dataset,
! 119: and the modify time and file mode
! 120: are set accordingly.
! 121:
! 122:
! 123: .B Sx
! 124: sends a single
! 125: .I file
! 126: with
! 127: .B XMODEM
! 128: or
! 129: .B XMODEM-1k
! 130: protocol
! 131: (sometimes incorrectly called "ymodem").
! 132: The user must supply the file name to both sending and receiving programs.
! 133:
! 134: If
! 135: .B sz
! 136: is invoked with $SHELL set and iff that variable contains the
! 137: string
! 138: .I "rsh"
! 139: ,
! 140: .I "rbash"
! 141: or
! 142: .I "rksh"
! 143: (restricted shell),
! 144: .B sz
! 145: operates in restricted mode.
! 146: Restricted mode restricts pathnames to the current directory and
! 147: PUBDIR (usually /usr/spool/uucppublic) and/or subdirectories
! 148: thereof.
! 149:
! 150:
! 151: The fourth form sends a single COMMAND to a ZMODEM receiver for execution.
! 152: .B Sz
! 153: exits with the COMMAND return value.
! 154: If COMMAND includes spaces or characters special to the shell,
! 155: it must be quoted.
! 156:
! 157:
! 158: The fifth form sends a single COMMAND to a ZMODEM receiver for execution.
! 159: .B Sz
! 160: exits as soon as the receiver has correctly received the command,
! 161: before it is executed.
! 162:
! 163:
! 164: The sixth form (sz -TT)
! 165: attempts to output all 256 code combinations to the terminal.
! 166: In you are having difficulty sending files,
! 167: this command lets you see which character codes are being
! 168: eaten by the operating system.
! 169:
! 170:
! 171: If
! 172: .B sz
! 173: is invoked with stdout and stderr to different datasets,
! 174: Verbose is set to 2, causing frame by frame progress reports
! 175: to stderr.
! 176: This may be disabled with the
! 177: .B q
! 178: option.
! 179: .PP
! 180: The meanings of the available options are:
! 181: .PP
! 182: .PD 0
! 183: .TP
! 184: .B "-+, --append"
! 185: Instruct the receiver to append transmitted data to an existing file
! 186: (ZMODEM only).
! 187: .TP
! 188: .B "-2, --twostop"
! 189: use two stop bits (if possible). Do not use this unless you know
! 190: what you are doing.
! 191: .TP
! 192: .B "-8, --try-8k"
! 193: Try to go up to 8KB blocksize. This is incompatible with standard zmodem,
! 194: but a common extension in the bbs world. (ZMODEM only).
! 195: .TP
! 196: .B "--start-8k"
! 197: Start with 8KB blocksize. Like --try-8k.
! 198: .TP
! 199: .B "-a, --ascii"
! 200: Convert NL characters in the transmitted file to CR/LF.
! 201: This is done by the sender for XMODEM and YMODEM, by the receiver
! 202: for ZMODEM.
! 203: .TP
! 204: .B "-b, --binary"
! 205: (ZMODEM) Binary override: transfer file without any translation.
! 206: .TP
! 207: .B "-B NUMBER, --bufsize NUMBER"
! 208: Use a readbuffer of
! 209: .B NUMBER
! 210: bytes. Default ist 16384, which should be enough
! 211: for most situations. If you have a slow machine or a bad disk interface
! 212: or suffer from other hardware problems you might want to increase
! 213: the buffersize.
! 214: .B -1
! 215: or
! 216: .B auto
! 217: use a buffer large enough to buffer the whole file. Be careful with this
! 218: option - things normally get worse, not better, if the machine starts
! 219: to swap.
! 220:
! 221: Using this option turns of memory mapping of the input file. This
! 222: increases memory and cpu usage.
! 223: .TP
! 224: .B "-c COMMAND, --command COMMAND"
! 225: Send COMMAND to the receiver for execution, return with COMMAND\'s exit status.
! 226: .TP
! 227: .B "-C N, --command-tries N"
! 228: Retry to send command N times (default: 11).
! 229: .TP
! 230: .B "-d, --dot-to-slash"
! 231: Change all instances of "." to "/" in the transmitted pathname.
! 232: Thus, C.omenB0000 (which is unacceptable to MSDOS or CP/M)
! 233: is transmitted as C/omenB0000.
! 234: If the resultant filename has more than 8 characters in the stem,
! 235: a "." is inserted to allow a total of eleven.
! 236:
! 237: This option enables the
! 238: .B "--full-path"
! 239: option.
! 240: .TP
! 241: .B "--delay-startup N"
! 242: Wait
! 243: .B N
! 244: seconds before doing anything.
! 245: .TP
! 246: .B "-e, --escape"
! 247: Escape all control characters;
! 248: normally XON, XOFF, DLE, CR-@-CR, and Ctrl-X are escaped.
! 249: .TP
! 250: .B"-E, --rename"
! 251: Force the sender to rename the new file if a file with the same
! 252: name already exists.
! 253: .TP
! 254: .B "-f, --full-path"
! 255: Send Full pathname.
! 256: Normally directory prefixes are stripped from the transmitted
! 257: filename.
! 258:
! 259: This is also turned on with to
! 260: .B "--dot-to-slash"
! 261: option.
! 262: .TP
! 263: .B "-h, --help"
! 264: give help.
! 265: .TP
! 266: .B "-i COMMAND, --immediate-command COMMAND"
! 267: Send COMMAND to the receiver for execution, return immediately
! 268: upon the receiving program's successful recption of the command.
! 269: .TP
! 270: .B "-k, --1k"
! 271: (XMODEM/YMODEM) Send files using 1024 byte blocks
! 272: rather than the default 128 byte blocks.
! 273: 1024 byte packets speed file transfers at high bit rates.
! 274: (ZMODEM streams the data for the best possible throughput.)
! 275: .TP
! 276: .B "-L N, --packetlen N"
! 277: Use ZMODEM sub-packets of length N.
! 278: A larger N (32 <= N <= 1024) gives slightly higher throughput,
! 279: a smaller N speeds error recovery.
! 280: The default is 128 below 300 baud, 256 above 300 baud, or 1024 above 2400 baud.
! 281: .TP
! 282: .B "-m N, --min-bps N"
! 283: Stop transmission if BPS-Rate (Bytes Per Second) falls below N for a
! 284: certain time (see --min-bps-time option).
! 285: .TP
! 286: .B "-M N, --min-bps-time"
! 287: Used together with --min-bps. Default is 120 (seconds).
! 288: .TP
! 289: .B "-l N, --framelen N"
! 290: Wait for the receiver to acknowledge correct data every
! 291: .B N
! 292: (32 <= N <= 1024)
! 293: characters.
! 294: This may be used to avoid network overrun when XOFF flow control is lacking.
! 295: .TP
! 296: .B "-n, --newer"
! 297: (ZMODEM) Send each file if
! 298: destination file does not exist.
! 299: Overwrite destination file if
! 300: source file is newer than the destination file.
! 301: .TP
! 302: .B "-N, --newer-or-longer"
! 303: (ZMODEM) Send each file if
! 304: destination file does not exist.
! 305: Overwrite destination file if
! 306: source file is newer or longer than the destination file.
! 307: .TP
! 308: .B "-o, --16-bit-crc"
! 309: (ZMODEM) Disable automatic selection of 32 bit CRC.
! 310: .TP
! 311: .B "-O, --disable-timeouts"
! 312: Disable read timeout handling. This makes lsz hang if the other side
! 313: doesn't send anything, but increases performance (not much) and
! 314: decreases system load (reduces number of system calls by about 50
! 315: percent).
! 316:
! 317: Use this option with care.
! 318: .TP
! 319: .B "-p, --protect"
! 320: (ZMODEM) Protect existing destination files by skipping transfer if the
! 321: destination file exists.
! 322: .TP
! 323: .B "-q, --quiet"
! 324: Quiet suppresses verbosity.
! 325: .TP
! 326: .B "-R, --restricted"
! 327: Restricted mode: restricts pathnames to the current directory and
! 328: PUBDIR (usually /usr/spool/uucppublic) and/or subdirectories
! 329: thereof.
! 330: .TP
! 331: .B "-r, --resume"
! 332: (ZMODEM) Resume interrupted file transfer.
! 333: If the source file is longer than the destination file,
! 334: the transfer commences at the offset in the source file that equals
! 335: the length of the destination file.
! 336: .TP
! 337: .B "-s HH:MM, --stop-at HH:MM"
! 338: Stop transmission at
! 339: .B HH
! 340: hours,
! 341: .B MM
! 342: minutes. Another variant, using
! 343: .B +N
! 344: instead of
! 345: .B HH:MM,
! 346: stops transmission in
! 347: .B N
! 348: seconds.
! 349: .TP
! 350: .B "-S, --timesync"
! 351: enable timesync protocol support. See timesync.doc for further
! 352: information.
! 353:
! 354: This option is incompatible with standard zmodem. Use it with care.
! 355: .TP
! 356: .B "--syslog[=off]"
! 357: turn syslogging on or off. the default is set at configure time.
! 358: This option is ignored if no syslog support is compiled in.
! 359: .TP
! 360: .B "-t TIM, --timeout TIM"
! 361: Change timeout to
! 362: .I TIM
! 363: tenths of seconds.
! 364: .TP
! 365: .B "-T, --turbo"
! 366: Do not escape certain characters (^P, ^P|0x80, telenet escape sequence
! 367: [CR + @]). This improves performance by about 1 percent and shouldn't
! 368: hurt in the normal case (but be careful - ^P might be useful if connected
! 369: through a terminal server).
! 370: .TP
! 371: .B "--tcp"
! 372: Try to initiate a TCP/IP connection. lsz will ask the receiving zmodem
! 373: to open a TCP/IP connection. All handshaking (which address / port to
! 374: use) will be done by the zmodem programs.
! 375:
! 376: You will normally not want to use this option as lrzsz is the only
! 377: zmodem which understands what to do (private extension). You might
! 378: want to use this option if the two programs are connected
! 379: (stdin/out) over a slow or bad (not 8bit clean) network connection.
! 380:
! 381: Use of this option imposes a security risk, somebody else could connect
! 382: to the port in between. See
! 383: .B SECURITY
! 384: for details.
! 385: .TP
! 386: .B "--tcp-client ADDRESS:PORT"
! 387: Act as a tcp/ip client: Connect to the given port.
! 388:
! 389: See
! 390: .B "--tcp-server"
! 391: for more information.
! 392:
! 393: .TP
! 394: .B "--tcp-server"
! 395: Act as a server: Open a socket, print out what to do, wait for connection.
! 396:
! 397: You will normally not want to use this option as lrzsz is the only
! 398: zmodem which understands what to do (private extension). You might
! 399: want to use this if you have to use zmodem (for which reason whatever),
! 400: and cannot use the
! 401: .B --tcp
! 402: option of
! 403: .I lsz
! 404: (perhaps because your telnet doesn't allow to spawn a local program
! 405: with stdin/stdout connected to the remote side).
! 406:
! 407: If you use this option you have to start
! 408: .I lsz
! 409: with the
! 410: .B --tcp-client ADDRESS:PORT
! 411: option.
! 412: .I lrz will print the address and port on startup.
! 413:
! 414: Use of this option imposes a security risk, somebody else could connect
! 415: to the port in between. See
! 416: .B SECURITY
! 417: for details.
! 418:
! 419: .TP
! 420: .B "-u"
! 421: Unlink the file after successful transmission.
! 422: .TP
! 423: .B "-U, --unrestrict"
! 424: Turn off restricted mode (this is not possible if running under a
! 425: restricted shell).
! 426: .TP
! 427: .B "-w N, --windowsize N"
! 428: Limit the transmit window size to N bytes (ZMODEM).
! 429: .TP
! 430: .B "-v, --verbose"
! 431: Verbose output to stderr. More v's generate more output.
! 432: .TP
! 433: .B "-X, --xmodem"
! 434: use XMODEM protocol.
! 435: .TP
! 436: .B "-y, --overwrite"
! 437: Instruct a ZMODEM receiving program to overwrite any existing file
! 438: with the same name.
! 439: .TP
! 440: .B "-Y, --overwrite-or-skip"
! 441: Instruct a ZMODEM receiving program to overwrite any existing file
! 442: with the same name,
! 443: and to skip any source files that do have a file with the same
! 444: pathname on the destination system.
! 445: .TP
! 446: .B "--ymodem"
! 447: use ZMODEM protocol.
! 448: .TP
! 449: .B "-Z, --zmodem"
! 450: use ZMODEM protocol.
! 451: .PD
! 452: .SH SECURITY
! 453: Restricted mode restricts pathnames to the current directory
! 454: and PUBDIR (usually /var/spool/uucppublic)
! 455: and/or subdirectories thereof, and disables remote command
! 456: execution.
! 457:
! 458: Restricted mode is entered if the
! 459: .B R
! 460: option is given or if lsz detects that it runs under a restricted
! 461: shell or if the environment variable ZMODEM_RESTRICTED is found.
! 462:
! 463: Restricted mode can be turned of with the
! 464: .B U
! 465: option if not running under a restricted shell.
! 466:
! 467: .TP
! 468: Use of the
! 469: .B --tcp-client
! 470: or
! 471: .B --tcp-server
! 472: options imposes a security risk, as somebody else could connect to
! 473: the port before you do it, and grab your data. If there's strong
! 474: demand for a more secure mode i might introduce some sort of
! 475: password challenge.
! 476:
! 477:
! 478: .SH ENVIRONMENT
! 479: .TP
! 480: .B ZNULLS
! 481: may be used to specify the number of nulls to send before a ZDATA frame.
! 482: .TP
! 483: .B SHELL
! 484: lsz recognizes a restricted shell if this variable includes
! 485: .I "rsh"
! 486: or
! 487: .I "rksh"
! 488: .TP
! 489: .B ZMODEM_RESTRICTED
! 490: lrz enters restricted mode if the variable is set.
! 491: .TP
! 492: .B TMPDIR
! 493: If this environment variable is set its content is used as the
! 494: directory to place in the answer file to a
! 495: .B timesync
! 496: request.
! 497: .B TMP
! 498: Used instead of TMPDIR if TMPDIR is not set. If neither TMPDIR nor
! 499: TMP is set /tmp will be used.
! 500: .SH EXAMPLES
! 501: .ne 7
! 502: .B "ZMODEM File Transfer"
! 503: (Unix to DSZ/ZCOMM/Professional-YAM)
! 504: .br
! 505: .B "% sz \-a *.c"
! 506: .br
! 507: This single command transfers all .c files in the current Unix directory
! 508: with conversion
! 509: .RB ( \-a )
! 510: to end of line conventions appropriate to the receiving environment.
! 511: With ZMODEM AutoDownload enabled, Professional-YAM and ZCOMM
! 512: will automatically recieve
! 513: the files after performing a security check.
! 514:
! 515: .br
! 516: .B "% sz \-Yan *.c *.h"
! 517: .br
! 518: Send only the .c and .h files that exist on both systems,
! 519: and are newer on the sending system than the
! 520: corresponding version on the receiving system, converting Unix to
! 521: DOS text format.
! 522: .br
! 523: .B
! 524: $ sz -\\Yan file1.c file2.c file3.c foo.h baz.h
! 525: .R
! 526: (for VMS)
! 527: .br
! 528:
! 529: .B "ZMODEM Command Download"
! 530: (Unix to Professional-YAM)
! 531: .br
! 532: cpszall:all
! 533: sz \-c "c:;cd /yam/dist"
! 534: sz \-ya $(YD)/*.me
! 535: sz \-yqb y*.exe
! 536: sz \-c "cd /yam"
! 537: sz \-i "!insms"
! 538: .br
! 539: This Makefile fragment uses
! 540: .B sz
! 541: to issue commands to Professional-YAM to change current disk and directory.
! 542: Next,
! 543: .B sz
! 544: transfers the
! 545: .I .me
! 546: files from the $YD directory, commanding the receiver to overwrite the old files
! 547: and to convert from Unix end of line conventions to PC-DOS conventions.
! 548: The third line transfers some
! 549: .I .exe
! 550: files.
! 551: The fourth and fifth lines command Pro-YAM to
! 552: change directory and execute a PC-DOS batch file
! 553: .I insms .
! 554: Since the batch file takes considerable time, the
! 555: .B "\-i"
! 556: form is used to allow
! 557: .B sz
! 558: to exit immediately.
! 559:
! 560: .B "XMODEM File Transfer"
! 561: (Unix to Crosstalk)
! 562: .br
! 563: %
! 564: .B "sx \-a foo.c"
! 565: .br
! 566: .B "ESC"
! 567: .br
! 568: .B "rx foo.c"
! 569: .br
! 570: The above three commands transfer a single file
! 571: from Unix to a PC and Crosstalk with
! 572: .I sz
! 573: translating Unix newlines to DOS CR/LF.
! 574: This combination is much slower and far less reliable than ZMODEM.
! 575: .SH ERROR MESSAGES
! 576: "Caught signal 99"
! 577: indicates the program was not properly compiled,
! 578: refer to "bibi(99)" in rbsb.c for details.
! 579: .SH SEE ALSO
! 580: rz(omen),
! 581: ZMODEM.DOC,
! 582: YMODEM.DOC,
! 583: Professional-YAM,
! 584: crc(omen),
! 585: sq(omen),
! 586: todos(omen),
! 587: tocpm(omen),
! 588: tomac(omen),
! 589: yam(omen)
! 590:
! 591: Compile time options required for various operating systems are described in
! 592: the source file.
! 593: .SH "VMS VERSION"
! 594: The VMS version does not support wild cards.
! 595: Because of VMS DCL, upper case option letters muse be represented
! 596: by \\ proceding the letter.
! 597:
! 598: The current VMS version does not support XMODEM, XMODEM-1k, or YMODEM.
! 599:
! 600: VMS C Standard I/O and RMS may interact to modify the file contents.
! 601: .SH FILES
! 602: 32 bit CRC code courtesy Gary S. Brown.
! 603:
! 604: sz.c, crctab.c, rbsb.c, zm.c, zmodem.h Unix source files
! 605:
! 606: sz.c, crctab.c, vrzsz.c, zm.c, zmodem.h, vmodem.h, vvmodem.c,
! 607: VMS source files.
! 608:
! 609: /tmp/szlog stores debugging output (sz -vv)
! 610: (szlog on VMS).
! 611: .SH "TESTING FEATURE"
! 612: The command "sz -T file"
! 613: exercises the
! 614: .B Attn
! 615: sequence error recovery by commanding
! 616: errors with unterminated packets.
! 617: The receiving program should complain five times about
! 618: binary data packets being too long.
! 619: Each time
! 620: .B sz
! 621: is interrupted,
! 622: it should send a ZDATA header followed by another defective packet.
! 623: If the receiver does not detect five long data packets,
! 624: the
! 625: .B Attn
! 626: sequence is not interrupting the sender, and the
! 627: .B Myattn
! 628: string in
! 629: .B sz.c
! 630: must be modified.
! 631:
! 632: After 5 packets,
! 633: .B sz
! 634: stops the "transfer" and
! 635: prints the total number of characters "sent" (Tcount).
! 636: The difference between Tcount and 5120 represents the number of characters
! 637: stored in various buffers when the Attn sequence is generated.
! 638: .SH BUGS
! 639: Calling
! 640: .I sz
! 641: from most versions of cu(1) doesn't work because cu's receive process
! 642: fights
! 643: .I sz
! 644: for characters from the modem.
! 645:
! 646: On at least one BSD system, sz would hang or exit when it got within
! 647: a few kilobytes of the end of file.
! 648: Using the "-w 8192" flag fixed the problem.
! 649: The real cause is unknown, perhaps a bug in the kernel TTY output routines.
! 650:
! 651: Programs that do not properly implement the specified file transfer protocol
! 652: may cause
! 653: .I sz
! 654: to "hang" the port for a minute or two.
! 655: This problem is corrected by using
! 656: ZCOMM, Pro-YAM, or other program with a correct implementation
! 657: of the specified protocol.
! 658:
! 659: Many programs claiming to support YMODEM only support XMODEM with 1k blocks,
! 660: and they often don't get that quite right.
! 661:
! 662: XMODEM transfers add up to 127 garbage bytes per file.
! 663: XMODEM-1k and YMODEM-1k transfers use 128 byte blocks
! 664: to avoid extra padding.
! 665:
! 666: YMODEM programs use the file length transmitted at the beginning of the
! 667: transfer to prune the file to the correct length; this may cause problems with
! 668: source files that grow during the course of the transfer.
! 669: This problem does not pertain to ZMODEM transfers, which preserve the exact
! 670: file length unconditionally.
! 671:
! 672: Most ZMODEM options are merely passed to the receiving program;
! 673: some do not implement all these options.
! 674:
! 675: Circular buffering and a ZMODEM sliding window should be used
! 676: when input is from pipes instead of acknowledging frames each 1024 bytes.
! 677: If no files can be opened,
! 678: .B sz
! 679: sends a ZMODEM command to echo a suitable complaint;
! 680: perhaps it should check for the presence of at least one accessible file before
! 681: getting hot and bothered.
! 682: The test mode leaves a zero length file on the receiving system.
! 683:
! 684: A few high speed modems have a firmware bug that drops characters when the
! 685: direction of high speed transmissson is reversed.
! 686: The environment variable ZNULLS may be used to specify the number of nulls to
! 687: send before a ZDATA frame.
! 688: Values of 101 for a 4.77 mHz PC and 124 for an AT are typical.
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