Annotation of src/usr.bin/patch/patch.1, Revision 1.9
1.9 ! jmc 1: .\" $OpenBSD: patch.1,v 1.8 2003/07/22 20:17:06 millert Exp $
1.6 jmc 2: .\" Copyright 1986, Larry Wall
3: .\"
4: .\" Redistribution and use in source and binary forms, with or without
5: .\" modification, are permitted provided that the following condition
6: .\" is met:
7: .\" 1. Redistributions of source code must retain the above copyright
8: .\" notice, this condition and the following disclaimer.
1.7 deraadt 9: .\"
1.6 jmc 10: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
11: .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
12: .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
13: .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
14: .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
15: .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
16: .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
17: .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
18: .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
19: .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
20: .\" SUCH DAMAGE.
21: .\"
1.9 ! jmc 22: .Dd July 23, 2003
! 23: .Dt PATCH 1
! 24: .Os
! 25: .Sh NAME
! 26: .Nm patch
! 27: .Nd apply a diff file to an original
! 28: .Sh SYNOPSIS
! 29: .Nm patch
! 30: .Op Cm options
! 31: .Op Ar origfile Op Ar patchfile
! 32: .Nm patch
! 33: .Pf \*(Lt Ar patchfile
! 34: .Sh DESCRIPTION
! 35: .Nm
1.1 deraadt 36: will take a patch file containing any of the four forms of difference
37: listing produced by the
1.9 ! jmc 38: .Xr diff 1
! 39: program and apply those differences to an original file,
! 40: producing a patched version.
1.1 deraadt 41: By default, the patched version is put in place of the original, with
1.9 ! jmc 42: the original file backed up to the same name with the extension
! 43: .Qq .orig
! 44: .Po
1.1 deraadt 45: or
1.9 ! jmc 46: .Qq ~
! 47: on systems that do not support long filenames
! 48: .Pc ,
! 49: or as specified by the
! 50: .Fl b ,
! 51: .Fl B ,
! 52: or
! 53: .Fl V
1.1 deraadt 54: switches.
55: The extension used for making backup files may also be specified in the
1.9 ! jmc 56: .Ev SIMPLE_BACKUP_SUFFIX
1.5 deraadt 57: environment variable, which is overridden by the above switches.
1.9 ! jmc 58: .Pp
1.1 deraadt 59: If the backup file already exists,
1.9 ! jmc 60: .Nm
1.1 deraadt 61: creates a new backup file name by changing the first lowercase letter
1.9 ! jmc 62: in the last component of the file's name into uppercase.
! 63: If there are no more lowercase letters in the name,
! 64: it removes the first character from the name.
! 65: It repeats this process until it comes up with a
1.1 deraadt 66: backup file that does not already exist.
1.9 ! jmc 67: .Pp
! 68: You may also specify where you want the output to go with the
! 69: .Fl o
1.1 deraadt 70: switch; if that file already exists, it is backed up first.
1.9 ! jmc 71: .Pp
1.1 deraadt 72: If
1.9 ! jmc 73: .Ar patchfile
1.1 deraadt 74: is omitted, or is a hyphen, the patch will be read from standard input.
1.9 ! jmc 75: .Pp
! 76: Upon startup,
! 77: .Nm
! 78: will attempt to determine the type of the diff listing,
1.1 deraadt 79: unless over-ruled by a
1.9 ! jmc 80: .Fl c ,
! 81: .Fl e ,
! 82: .Fl n ,
1.1 deraadt 83: or
1.9 ! jmc 84: .Fl u
1.1 deraadt 85: switch.
86: Context diffs (old-style, new-style, and unified) and
87: normal diffs are applied by the
1.9 ! jmc 88: .Nm
1.1 deraadt 89: program itself, while ed diffs are simply fed to the
1.9 ! jmc 90: .Xr ed 1
1.1 deraadt 91: editor via a pipe.
1.9 ! jmc 92: .Pp
! 93: .Nm
1.1 deraadt 94: will try to skip any leading garbage, apply the diff,
95: and then skip any trailing garbage.
96: Thus you could feed an article or message containing a
97: diff listing to
1.9 ! jmc 98: .Nm patch ,
1.1 deraadt 99: and it should work.
100: If the entire diff is indented by a consistent amount,
101: this will be taken into account.
1.9 ! jmc 102: .Pp
1.1 deraadt 103: With context diffs, and to a lesser extent with normal diffs,
1.9 ! jmc 104: .Nm
1.1 deraadt 105: can detect when the line numbers mentioned in the patch are incorrect,
106: and will attempt to find the correct place to apply each hunk of the patch.
107: As a first guess, it takes the line number mentioned for the hunk, plus or
108: minus any offset used in applying the previous hunk.
109: If that is not the correct place,
1.9 ! jmc 110: .Nm
1.1 deraadt 111: will scan both forwards and backwards for a set of lines matching the context
112: given in the hunk.
113: First
1.9 ! jmc 114: .Nm
1.1 deraadt 115: looks for a place where all lines of the context match.
116: If no such place is found, and it's a context diff, and the maximum fuzz factor
117: is set to 1 or more, then another scan takes place ignoring the first and last
118: line of context.
119: If that fails, and the maximum fuzz factor is set to 2 or more,
120: the first two and last two lines of context are ignored,
121: and another scan is made.
1.9 ! jmc 122: .Pq The default maximum fuzz factor is 2.
! 123: .Pp
1.1 deraadt 124: If
1.9 ! jmc 125: .Nm
! 126: cannot find a place to install that hunk of the patch, it will put the hunk
! 127: out to a reject file, which normally is the name of the output file plus
! 128: .Qq .rej
! 129: .Po
! 130: or
! 131: .Qq #
! 132: on systems that do not support long filenames
! 133: .Pc .
1.1 deraadt 134: (Note that the rejected hunk will come out in context diff form whether the
135: input patch was a context diff or a normal diff.
136: If the input was a normal diff, many of the contexts will simply be null.)
137: The line numbers on the hunks in the reject file may be different than
138: in the patch file: they reflect the approximate location patch thinks the
139: failed hunks belong in the new file rather than the old one.
1.9 ! jmc 140: .Pp
1.1 deraadt 141: As each hunk is completed, you will be told whether the hunk succeeded or
142: failed, and which line (in the new file)
1.9 ! jmc 143: .Nm
1.1 deraadt 144: thought the hunk should go on.
1.9 ! jmc 145: If this is different from the line number specified in the diff,
! 146: you will be told the offset.
1.1 deraadt 147: A single large offset MAY be an indication that a hunk was installed in the
148: wrong place.
149: You will also be told if a fuzz factor was used to make the match, in which
150: case you should also be slightly suspicious.
1.9 ! jmc 151: .Pp
1.1 deraadt 152: If no original file is specified on the command line,
1.9 ! jmc 153: .Nm
1.1 deraadt 154: will try to figure out from the leading garbage what the name of the file
155: to edit is.
156: In the header of a context diff, the filename is found from lines beginning
1.9 ! jmc 157: with
! 158: .Qq ***
! 159: or
! 160: .Qq --- ,
! 161: with the shortest name of an existing file winning.
! 162: Only context diffs have lines like that, but if there is an
! 163: .Qq Index:
1.1 deraadt 164: line in the leading garbage,
1.9 ! jmc 165: .Nm
1.1 deraadt 166: will try to use the filename from that line.
167: The context diff header takes precedence over an Index line.
168: If no filename can be intuited from the leading garbage, you will be asked
169: for the name of the file to patch.
1.9 ! jmc 170: .Pp
1.1 deraadt 171: If the original file cannot be found or is read-only, but a suitable
172: SCCS or RCS file is handy,
1.9 ! jmc 173: .Nm
1.1 deraadt 174: will attempt to get or check out the file.
1.9 ! jmc 175: .Pp
! 176: Additionally, if the leading garbage contains a
! 177: .Qq Prereq:\ \&
! 178: line,
! 179: .Nm
1.1 deraadt 180: will take the first word from the prerequisites line (normally a version
181: number) and check the input file to see if that word can be found.
182: If not,
1.9 ! jmc 183: .Nm
1.1 deraadt 184: will ask for confirmation before proceeding.
1.9 ! jmc 185: .Pp
1.1 deraadt 186: The upshot of all this is that you should be able to say, while in a news
187: interface, the following:
1.9 ! jmc 188: .Pp
! 189: .Dl | patch -d /usr/src/local/blurfl
! 190: .Pp
1.1 deraadt 191: and patch a file in the blurfl directory directly from the article containing
192: the patch.
1.9 ! jmc 193: .Pp
1.1 deraadt 194: If the patch file contains more than one patch,
1.9 ! jmc 195: .Nm
1.1 deraadt 196: will try to apply each of them as if they came from separate patch files.
197: This means, among other things, that it is assumed that the name of the file
198: to patch must be determined for each diff listing,
199: and that the garbage before each diff listing will
200: be examined for interesting things such as filenames and revision level, as
201: mentioned previously.
1.9 ! jmc 202: .Pp
! 203: .Nm
1.1 deraadt 204: recognizes the following switches:
1.9 ! jmc 205: .Bl -tag -width Ds
! 206: .It Fl b , Fl Fl suffix
! 207: Causes the next argument to be interpreted as the backup extension, to be
! 208: used in place of
! 209: .Qq .orig
! 210: or
! 211: .Qq ~ .
! 212: .It Fl B , Fl Fl prefix
! 213: Causes the next argument to be interpreted as a prefix to the backup file
! 214: name.
! 215: If this argument is specified, any argument from
! 216: .Fl b
! 217: will be ignored.
! 218: .It Fl c , Fl Fl context
! 219: Forces
! 220: .Nm
1.1 deraadt 221: to interpret the patch file as a context diff.
1.9 ! jmc 222: .It Fl C , Fl Fl check
! 223: Checks that the patch would apply cleanly, but does not modify anything.
! 224: .It Fl d , Fl Fl directory
! 225: Causes
! 226: .Nm
! 227: to interpret the next argument as a directory, and
! 228: .Xr cd 1
! 229: to it before doing anything else.
! 230: .It Fl D , Fl Fl ifdef
! 231: Causes
! 232: .Nm
! 233: to use the
! 234: .Qq #ifdef...#endif
! 235: construct to mark changes.
1.1 deraadt 236: The argument following will be used as the differentiating symbol.
237: Note that, unlike the C compiler, there must be a space between the
1.9 ! jmc 238: .Fl D
1.1 deraadt 239: and the argument.
1.9 ! jmc 240: .It Fl e , Fl Fl ed
! 241: Forces
! 242: .Nm
! 243: to interpret the patch file as an
! 244: .Xr ed 1
! 245: script.
! 246: .It Fl E , Fl Fl remove-empty-files
! 247: Causes
! 248: .Nm
1.1 deraadt 249: to remove output files that are empty after the patches have been applied.
1.9 ! jmc 250: .It Fl f , Fl Fl force
! 251: Forces
! 252: .Nm
1.1 deraadt 253: to assume that the user knows exactly what he or she is doing, and to not
1.9 ! jmc 254: ask any questions.
! 255: It assumes the following:
! 256: skip patches for which a file to patch can't be found;
! 257: patch files even though they have the wrong version for the
! 258: .Qq Prereq:
! 259: line in the patch;
! 260: and assume that patches are not reversed even if they look like they are.
1.1 deraadt 261: This option does not suppress commentary; use
1.9 ! jmc 262: .Fl s
1.1 deraadt 263: for that.
1.9 ! jmc 264: .It Fl t , Fl Fl batch
! 265: Similar to
! 266: .Fl f ,
1.1 deraadt 267: in that it suppresses questions, but makes some different assumptions:
1.9 ! jmc 268: skip patches for which a file to patch can't be found (the same as
! 269: .Fl f ) ;
! 270: skip patches for which the file has the wrong version for the
! 271: .Qq Prereq:
! 272: line in the patch;
! 273: and assume that patches are reversed if they look like they are.
! 274: .It Xo
! 275: .Fl F Ns Aq Ar number ,
! 276: .Fl Fl fuzz Aq Ar number
! 277: .Xc
! 278: Sets the maximum fuzz factor.
1.1 deraadt 279: This switch only applies to context diffs, and causes
1.9 ! jmc 280: .Nm
1.1 deraadt 281: to ignore up to that many lines in looking for places to install a hunk.
282: Note that a larger fuzz factor increases the odds of a faulty patch.
283: The default fuzz factor is 2, and it may not be set to more than
284: the number of lines of context in the context diff, ordinarily 3.
1.9 ! jmc 285: .It Fl l , Fl Fl ignore-whitespace
! 286: Causes the pattern matching to be done loosely, in case the tabs and
1.1 deraadt 287: spaces have been munged in your input file.
288: Any sequence of whitespace in the pattern line will match any sequence
289: in the input file.
290: Normal characters must still match exactly.
291: Each line of the context must still match a line in the input file.
1.9 ! jmc 292: .It Fl n , Fl Fl normal
! 293: Forces
! 294: .Nm
1.1 deraadt 295: to interpret the patch file as a normal diff.
1.9 ! jmc 296: .It Fl N , Fl Fl forward
! 297: Causes
! 298: .Nm
1.1 deraadt 299: to ignore patches that it thinks are reversed or already applied.
300: See also
1.9 ! jmc 301: .Fl R .
! 302: .It Fl o , Fl Fl output
! 303: Causes the next argument to be interpreted as the output file name.
! 304: .It Xo
! 305: .Fl p Ns Aq Ar number ,
! 306: .Fl Fl strip Aq Ar number
! 307: .Xc
! 308: Sets the pathname strip count,
! 309: which controls how pathnames found in the patch file are treated,
! 310: in case you keep your files in a different directory than the person who sent
1.1 deraadt 311: out the patch.
312: The strip count specifies how many slashes are to be stripped from
313: the front of the pathname.
314: (Any intervening directory names also go away.)
315: For example, supposing the filename in the patch file was
1.9 ! jmc 316: .Pa /u/howard/src/blurfl/blurfl.c :
! 317: .Pp
! 318: Setting
! 319: .Fl p
1.1 deraadt 320: or
1.9 ! jmc 321: .Fl p Ns Ar 0
! 322: gives the entire pathname unmodified.
! 323: .Pp
! 324: .Fl p Ns Ar 1
1.1 deraadt 325: gives
1.9 ! jmc 326: .Pp
! 327: .D1 Pa u/howard/src/blurfl/blurfl.c
! 328: .Pp
! 329: without the leading slash.
! 330: .Pp
! 331: .Fl p Ns Ar 4
1.1 deraadt 332: gives
1.9 ! jmc 333: .Pp
! 334: .D1 Pa blurfl/blurfl.c
! 335: .Pp
! 336: Not specifying
! 337: .Fl p
! 338: at all just gives you
! 339: .Pa blurfl.c ,
! 340: unless all of the directories in the leading path
! 341: .Pq Pa u/howard/src/blurfl
! 342: exist and that path is relative,
1.1 deraadt 343: in which case you get the entire pathname unmodified.
344: Whatever you end up with is looked for either in the current directory,
345: or the directory specified by the
1.9 ! jmc 346: .Fl d
1.1 deraadt 347: switch.
1.9 ! jmc 348: .It Fl r , Fl Fl reject-file
! 349: Causes the next argument to be interpreted as the reject file name.
! 350: .It Fl R , Fl Fl reverse
! 351: Tells
! 352: .Nm
1.1 deraadt 353: that this patch was created with the old and new files swapped.
354: (Yes, I'm afraid that does happen occasionally, human nature being what it
355: is.)
1.9 ! jmc 356: .Nm
1.1 deraadt 357: will attempt to swap each hunk around before applying it.
358: Rejects will come out in the swapped format.
359: The
1.9 ! jmc 360: .Fl R
1.1 deraadt 361: switch will not work with ed diff scripts because there is too little
362: information to reconstruct the reverse operation.
1.9 ! jmc 363: .Pp
1.1 deraadt 364: If the first hunk of a patch fails,
1.9 ! jmc 365: .Nm
1.1 deraadt 366: will reverse the hunk to see if it can be applied that way.
367: If it can, you will be asked if you want to have the
1.9 ! jmc 368: .Fl R
1.1 deraadt 369: switch set.
370: If it can't, the patch will continue to be applied normally.
371: (Note: this method cannot detect a reversed patch if it is a normal diff
372: and if the first command is an append (i.e. it should have been a delete)
373: since appends always succeed, due to the fact that a null context will match
374: anywhere.
375: Luckily, most patches add or change lines rather than delete them, so most
376: reversed normal diffs will begin with a delete, which will fail, triggering
377: the heuristic.)
1.9 ! jmc 378: .It Xo
! 379: .Fl s , Fl Fl quiet ,
! 380: .Fl Fl silent
! 381: .Xc
! 382: Makes
! 383: .Nm
1.1 deraadt 384: do its work silently, unless an error occurs.
1.9 ! jmc 385: .It Fl u , Fl Fl unified
! 386: Forces
! 387: .Nm
1.1 deraadt 388: to interpret the patch file as a unified context diff (a unidiff).
1.9 ! jmc 389: .It Fl v , Fl Fl version
! 390: Causes
! 391: .Nm
1.1 deraadt 392: to print out its revision header and patch level.
1.9 ! jmc 393: .It Fl V , Fl Fl version-control
! 394: Causes the next argument to be interpreted as a method for creating
! 395: backup file names.
! 396: The type of backups made can also be given in the
! 397: .Ev VERSION_CONTROL
1.1 deraadt 398: environment variable, which is overridden by this option.
399: The
1.9 ! jmc 400: .Fl B
1.1 deraadt 401: option overrides this option, causing the prefix to always be used for
402: making backup file names.
403: The value of the
1.9 ! jmc 404: .Ev VERSION_CONTROL
1.1 deraadt 405: environment variable and the argument to the
1.9 ! jmc 406: .Fl V
! 407: option are like the GNU Emacs
! 408: .Dq version-control
! 409: variable; they also recognize synonyms that are more descriptive.
! 410: The valid values are (unique abbreviations are accepted):
! 411: .Bl -tag -width Ds -offset indent
! 412: .It t , numbered
1.1 deraadt 413: Always make numbered backups.
1.9 ! jmc 414: .It nil , existing
! 415: Make numbered backups of files that already have them,
! 416: simple backups of the others.
1.1 deraadt 417: This is the default.
1.9 ! jmc 418: .It never , simple
1.1 deraadt 419: Always make simple backups.
1.9 ! jmc 420: .El
! 421: .It Xo
! 422: .Fl x Ns Aq Ar number ,
! 423: .Fl Fl debug Aq Ar number
! 424: .Xc
! 425: Sets internal debugging flags, and is of interest only to
! 426: .Nm
1.1 deraadt 427: patchers.
1.9 ! jmc 428: .El
! 429: .Sh NOTES FOR PATCH SENDERS
1.1 deraadt 430: There are several things you should bear in mind if you are going to
1.9 ! jmc 431: be sending out patches:
! 432: .Pp
! 433: First, you can save people a lot of grief by keeping a
! 434: .Pa patchlevel.h
! 435: file which is patched to increment the patch level as the first diff in the
1.1 deraadt 436: patch file you send out.
1.9 ! jmc 437: If you put a
! 438: .Qq Prereq:
! 439: line in with the patch, it won't let them apply
1.1 deraadt 440: patches out of order without some warning.
1.9 ! jmc 441: .Pp
1.1 deraadt 442: Second, make sure you've specified the filenames right, either in a
1.9 ! jmc 443: context diff header, or with an
! 444: .Qq Index:
! 445: line.
1.1 deraadt 446: If you are patching something in a subdirectory, be sure to tell the patch
1.4 aaron 447: user to specify a
1.9 ! jmc 448: .Fl p
1.1 deraadt 449: switch as needed.
1.9 ! jmc 450: .Pp
1.1 deraadt 451: Third, you can create a file by sending out a diff that compares a
452: null file to the file you want to create.
453: This will only work if the file you want to create doesn't exist already in
454: the target directory.
1.9 ! jmc 455: .Pp
1.1 deraadt 456: Fourth, take care not to send out reversed patches, since it makes people wonder
457: whether they already applied the patch.
1.9 ! jmc 458: .Pp
1.1 deraadt 459: Fifth, while you may be able to get away with putting 582 diff listings into
460: one file, it is probably wiser to group related patches into separate files in
461: case something goes haywire.
1.9 ! jmc 462: .Sh ENVIRONMENT
! 463: .Bl -tag -width "SIMPLE_BACKUP_SUFFIX" -compact
! 464: .It Ev TMPDIR
! 465: Directory to put temporary files in; default is
! 466: .Pa /tmp .
! 467: .It Ev SIMPLE_BACKUP_SUFFIX
! 468: Extension to use for backup file names instead of
! 469: .Qq .orig
! 470: or
! 471: .Qq ~ .
! 472: .It Ev VERSION_CONTROL
! 473: Selects when numbered backup files are made.
! 474: .El
! 475: .Sh FILES
! 476: .Bl -tag -width Ds
! 477: .It Pa $TMPDIR/patch*
! 478: .El
! 479: .Sh DIAGNOSTICS
1.1 deraadt 480: Too many to list here, but generally indicative that
1.9 ! jmc 481: .Nm
1.1 deraadt 482: couldn't parse your patch file.
1.9 ! jmc 483: .Pp
! 484: The message
! 485: .Qq Hmm...
! 486: indicates that there is unprocessed text in the patch file and that
! 487: .Nm
1.1 deraadt 488: is attempting to intuit whether there is a patch in that text and, if so,
489: what kind of patch it is.
1.9 ! jmc 490: .Pp
! 491: .Nm
1.1 deraadt 492: will exit with a non-zero status if any reject files were created.
493: When applying a set of patches in a loop it behooves you to check this
494: exit status so you don't apply a later patch to a partially patched file.
1.9 ! jmc 495: .Sh SEE ALSO
! 496: .Xr diff 1
! 497: .Sh AUTHORS
! 498: .An Larry Wall Aq lwall@netlabs.com
! 499: with many other contributors.
! 500: .Sh CAVEATS
! 501: .Nm
1.1 deraadt 502: cannot tell if the line numbers are off in an ed script, and can only detect
1.9 ! jmc 503: bad line numbers in a normal diff when it finds a
! 504: .Qq change
! 505: or a
! 506: .Qq delete
! 507: command.
1.1 deraadt 508: A context diff using fuzz factor 3 may have the same problem.
509: Until a suitable interactive interface is added, you should probably do
510: a context diff in these cases to see if the changes made sense.
511: Of course, compiling without errors is a pretty good indication that the patch
512: worked, but not always.
1.9 ! jmc 513: .Pp
! 514: .Nm
1.1 deraadt 515: usually produces the correct results, even when it has to do a lot of
516: guessing.
517: However, the results are guaranteed to be correct only when the patch is
518: applied to exactly the same version of the file that the patch was
519: generated from.
1.9 ! jmc 520: .Sh BUGS
! 521: Could be smarter about partial matches, excessively deviant offsets and
1.1 deraadt 522: swapped code, but that would take an extra pass.
1.9 ! jmc 523: .Pp
! 524: Check patch mode
! 525: .Pq Fl C
1.3 espie 526: will fail if you try to check several patches in succession that build on
1.9 ! jmc 527: each other.
! 528: The whole code of
! 529: .Nm
1.3 espie 530: would have to be restructured to keep temporary files around so that it can
531: handle this situation.
1.9 ! jmc 532: .Pp
1.1 deraadt 533: If code has been duplicated (for instance with #ifdef OLDCODE ... #else ...
534: #endif),
1.9 ! jmc 535: .Nm
1.1 deraadt 536: is incapable of patching both versions, and, if it works at all, will likely
537: patch the wrong one, and tell you that it succeeded to boot.
1.9 ! jmc 538: .Pp
1.1 deraadt 539: If you apply a patch you've already applied,
1.9 ! jmc 540: .Nm
1.1 deraadt 541: will think it is a reversed patch, and offer to un-apply the patch.
542: This could be construed as a feature.