1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
|
<!--%hypertext -->
<!-- mod_rewrite.html -->
<!-- Documentation for the mod_rewrite Apache module -->
<html>
<head>
<title>Apache module mod_rewrite</title>
</head>
<body>
<!--#include virtual="header.html" -->
<h1>Module mod_rewrite (Version 3.0)</h1>
This module is contained in the <code>mod_rewrite.c</code> file, with Apache
1.2 and later. It provides a rule-based rewriting engine to rewrite requested
URLs on the fly. <code>mod_rewrite</code> is not compiled into the server by
default. To use <code>mod_rewrite</code> you have to enable the following line
in the server build Configuration file:
<pre>
Module rewrite_module mod_rewrite.o
</pre>
<h2>Summary</h2>
This module uses a rule-based rewriting engine (based on a
regular-expression parser) to rewrite requested URLs on the fly.
<p>
It supports an unlimited number of additional rule conditions (which can
operate on a lot of variables, including HTTP headers) for granular
matching and external database lookups (either via plain text
tables, DBM hash files or external processes) for advanced URL
substitution.
<p>
It operates on the full URLs (including the PATH_INFO part) both in
per-server context (httpd.conf) and per-dir context (.htaccess) and even
can generate QUERY_STRING parts on result. The rewritten result can lead to internal sub-processing, external request redirection or to internal proxy throughput.
</b>
<p>
The latest version can be found on<br>
<a href="http://www.engelschall.com/sw/mod_rewrite/">
<code><b>http://www.engelschall.com/sw/mod_rewrite/</b></code></a>
<p>
Copyright © 1996,1997 <b>The Apache Group</b>, All rights reserved.<br>
Copyright © 1996,1997 <i>Ralf S. Engelschall</i>, All rights reserved.
<p>
Written for <b>The Apache Group</b> by
<blockquote>
<i>Ralf S. Engelschall</i><br>
<a href="mailto:rse@engelschall.com"><tt>rse@engelschall.com</tt></a><br>
<a href="http://www.engelschall.com/"><tt>www.engelschall.com</tt></a>
</blockquote>
<!--%hypertext -->
<HR>
<!--/%hypertext -->
<p>
<h2>Directives</h2>
<ul>
<li><a href="#RewriteEngine">RewriteEngine</a>
<li><a href="#RewriteOptions">RewriteOptions</a>
<li><a href="#RewriteLog">RewriteLog</a>
<li><a href="#RewriteLogLevel">RewriteLogLevel</a>
<li><a href="#RewriteMap">RewriteMap</a>
<li><a href="#RewriteBase">RewriteBase</a>
<li><a href="#RewriteCond">RewriteCond</a>
<li><a href="#RewriteRule">RewriteRule</a>
</ul>
<!--%hypertext -->
<hr>
<!--/%hypertext -->
<center>
<a name="Configuration">
<h1>Configuration Directives</h1>
</a>
</center>
<a name="RewriteEngine"><h3>RewriteEngine</h3></a>
<strong>Syntax:</strong> <code>RewriteEngine</code> {<code>on,off</code>}<br>
<strong>Default:</strong> <strong><code>RewriteEngine off</code></strong><br>
<strong>Context:</strong> server config, virtual host, per-directory config<br>
<p>
The <tt>RewriteEngine</tt> directive enables or disables the
runtime rewriting engine. If it is set to <code>off</code> this module does
no runtime processing at all. It does not even update the <tt>SCRIPT_URx</tt>
environment variables.
<p>
Use this directive to disable the module instead of commenting out
all <tt>RewriteRule</tt> directives!
<p>
<hr noshade size=1>
<p>
<a name="RewriteOptions"><h3>RewriteOptions</h3></a>
<strong>Syntax:</strong> <code>RewriteOptions</code> <em>Option</em> ...<br>
<strong>Default:</strong> -<em>None</em>-<br>
<strong>Context:</strong> server config, virtual host, per-directory config<br>
<p>
The <tt>RewriteOption</tt> directive sets some special options for the
current per-server or per-directory configuration. The <em>Option</em>
strings can be one of the following:
<ul>
<li>'<strong><code>inherit</code></strong>'<br>
This forces the current configuration to inherit the configuration of the
parent. In per-virtual-server context this means that the maps,
conditions and rules of the main server gets inherited. In per-directory
context this means that conditions and rules of the parent directory's
<tt>.htaccess</tt> configuration gets inherited.
<p>
</ul>
<p>
<hr noshade size=1>
<p>
<a name="RewriteLog"><h3>RewriteLog</h3></a>
<strong>Syntax:</strong> <code>RewriteLog</code> <em>Filename</em><br>
<strong>Default:</strong> -<em>None</em>-<br>
<strong>Context:</strong> server config, virtual host<br>
<p>
The <tt>RewriteLog</tt> directive sets the name of the file to which the
server logs any rewriting actions it performs. If the name does not begin
with a slash ('<tt>/</tt>') then it is assumed to be relative to the
<em>Server Root</em>. The directive should occur only once per server
config.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
To disable the logging of rewriting actions it is not recommended
to set <em>Filename</em>
to <code>/dev/null</code>, because although the rewriting engine does
not create output to a logfile it still creates the logfile
output internally. <b>This will slow down the server with no advantage to the
administrator!</b>
To disable logging either remove or comment out the
<tt>RewriteLog</tt> directive or use <tt>RewriteLogLevel 0</tt>!
</td></tr>
</table>
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
SECURITY: See the <a
href="../misc/security_tips.html">Apache Security
Tips</a> document for details on why your security could be compromised if the
directory where logfiles are stored is writable by anyone other than the user
that starts the server.
</td></tr>
</table>
<p>
<b>Example:</b>
<blockquote>
<pre>
RewriteLog "/usr/local/var/apache/logs/rewrite.log"
</pre>
</blockquote>
<p>
<hr noshade size=1>
<p>
<a name="RewriteLogLevel"><h3>RewriteLogLevel</h3></a>
<strong>Syntax:</strong> <code>RewriteLogLevel</code> <em>Level</em><br>
<strong>Default:</strong> <strong><code>RewriteLogLevel 0</code></strong><br>
<strong>Context:</strong> server config, virtual host<br>
<p>
The <tt>RewriteLogLevel</tt> directive set the verbosity level of the rewriting
logfile. The default level 0 means no logging, while 9 or more means
that practically all actions are logged.
<p>
To disable the logging of rewriting actions simply set <em>Level</em> to 0.
This disables all rewrite action logs.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
<b>Notice:</b> Using a high value for <i>Level</i> will slow down your Apache
server dramatically! Use the rewriting logfile only for debugging or at least
at <em>Level</em> not greater than 2!
</td></tr>
</table>
<p>
<b>Example:</b>
<blockquote>
<pre>
RewriteLogLevel 3
</pre>
</blockquote>
<p>
<hr noshade size=1>
<p>
<a name="RewriteMap"><h3>RewriteMap</h3></a>
<strong>Syntax:</strong> <code>RewriteMap</code> <em>Mapname</em> <code>{txt,dbm,prg}:</code><em>Filename</em><br>
<strong>Default:</strong> not used per default<br>
<strong>Context:</strong> server config, virtual host<br>
<p>
The <tt>RewriteMap</tt> directive defines an external <em>Rewriting Map</em>
which can be used inside rule substitution strings by the mapping-functions
to insert/substitute fields through a key lookup.
<p>
The <a name="mapfunc"><em>Mapname</em></a> is the name of the map and will
be used to specify a mapping-function for the substitution strings of a
rewriting rule via
<blockquote><strong>
<code>${</code> <em>Mapname</em> <code>:</code> <em>LookupKey</em>
<code>|</code> <em>DefaultValue</em> <code>}</code>
</strong></blockquote>
When such a directive occurs the map <em>Mapname</em>
is consulted and the key <em>LookupKey</em> is looked-up. If the key is
found, the map-function directive is substituted by <em>SubstValue</em>. If
the key is not found then it is substituted by <em>DefaultValue</em>.
<p>
The <em>Filename</em> must be a valid Unix filepath, containing one
of the following formats:
<ol>
<li><b>Plain Text Format</b>
<p>
This is a ASCII file which contains either blank lines, comment lines
(starting with a '#' character) or
<blockquote><strong>
<em>MatchingKey</em> <em>SubstValue</em>
</strong></blockquote>
pairs - one per line. You can create such files either manually,
using your favorite editor, or by using the programs
<tt>mapcollect</tt> and <tt>mapmerge</tt> from the <tt>support</tt>
directory of the <b>mod_rewrite</b> distribution.
<p>
To declare such a map prefix, <em>Filename</em> with a <code>txt:</code>
string as in the following example:
<p>
<table border=2 cellspacing=1 cellpadding=5 bgcolor="#d0d0d0">
<tr><td><pre>
#
# map.real-to-user -- maps realnames to usernames
#
Ralf.S.Engelschall rse # Bastard Operator From Hell
Dr.Fred.Klabuster fred # Mr. DAU
</pre></td></tr>
</table>
<p>
<table border=2 cellspacing=1 cellpadding=5 bgcolor="#d0d0d0">
<tr><td><pre>
RewriteMap real-to-host txt:/path/to/file/map.real-to-user
</pre></td></tr>
</table>
<p>
<li><b>DBM Hashfile Format</b>
<p>
This is a binary NDBM format file containing the
same contents as the <em>Plain Text Format</b> files. You can create
such a file with any NDBM tool or with the <tt>dbmmanage</tt> program
from the <tt>support</tt> directory of the Apache distribution.
<p>
To declare such a map prefix <em>Filename</em> with a <code>dbm:</code>
string.
<p>
<li><b>Program Format</b>
<p>
This is a Unix executable, not a lookup file. To create it you can use
the language of your choice, but the result has to be a run-able Unix
binary (i.e. either object-code or a script with the
magic cookie trick '<tt>#!/path/to/interpreter</tt>' as the first line).
<p>
This program gets started once at startup of the Apache servers and then
communicates with the rewriting engine over its <tt>stdin</tt> and
<tt>stdout</tt> file-handles. For each map-function lookup it will
receive the key to lookup as a newline-terminated string on
<tt>stdin</tt>. It then has to give back the looked-up value as a
newline-terminated string on <tt>stdout</tt> or the four-character string
``<tt>NULL</tt>'' if it fails (i.e. there is no corresponding value
for the given key). A trivial program which will implement a 1:1 map
(i.e. key == value) could be:
<p>
<table border=2 cellspacing=1 cellpadding=5 bgcolor="#d0d0d0">
<tr><td><pre>
#!/usr/bin/perl
$| = 1;
while (<STDIN>) {
# ...here any transformations
# or lookups should occur...
print $_;
}
</pre></td></tr>
</table>
<p>
<b>But be very careful:</b><br>
<ol>
<li>``<i>Keep the program simple, stupid</i>'' (KISS), because
if this program hangs it will lead to a hang of the Apache server
when the rule occurs.
<li>Avoid one common mistake: never do buffered I/O on <tt>stdout</tt>!
This will cause a deadloop! Hence the ``<tt>$|=1</tt>'' in the above
example...
</ol>
<p>
To declare such a map prefix <em>Filename</em> with a <code>prg:</code>
string.
</ol>
The <tt>RewriteMap</tt> directive can occur more than once. For each
mapping-function use one <tt>RewriteMap</tt> directive to declare its
rewriting mapfile. While you cannot <b>declare</b> a map in per-directory
context it is of course possible to <b>use</b> this map in per-directory
context.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
For plain text and DBM format files the looked-up keys are cached in-core
until the <tt>mtime</tt> of the mapfile changes or the server does a
restart. This way you can have map-functions in rules which are used
for <b>every</b> request. This is no problem, because the external lookup
only happens once!
</td></tr>
</table>
<p>
<hr noshade size=1>
<p>
<a name="RewriteBase"><h3>RewriteBase</h3></a>
<strong>Syntax:</strong> <code>RewriteBase</code> <em>BaseURL</em><br>
<strong>Default:</strong> <em>default is the physical directory path</em><br>
<strong>Context:</strong> per-directory config<br>
<p>
The <tt>RewriteBase</tt> directive explicitly sets the base URL for
per-directory rewrites. As you will see below, <tt>RewriteRule</tt> can be
used in per-directory config files (<tt>.htaccess</tt>). There it will act
locally, i.e. the local directory prefix is stripped at this stage of
processing and your rewriting rules act only on the remainder. At the end
it is automatically added.
<p>
When a substitution occurs for a new URL, this module has to
re-inject the URL into the server processing. To be able to do this it needs
to know what the corresponding URL-prefix or URL-base is. By default this
prefix is the corresponding filepath itself. <b>But at most websites URLs are
<b>NOT</b> directly related to physical filename paths, so this assumption
will be usually be wrong!</b> There you have to use the <tt>RewriteBase</tt>
directive to specify the correct URL-prefix.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
So, if your webserver's URLs are <b>not</b> directly
related to physical file paths, you have to use <tt>RewriteBase</tt> in every
<tt>.htaccess</tt> files where you want to use <tt>RewriteRule</tt>
directives.
</td></tr>
</table>
<p>
<b>Example:</b>
<blockquote>
Assume the following per-directory config file:
<p>
<table border=2 cellspacing=1 cellpadding=5 bgcolor="#d0d0d0">
<tr><td><pre>
#
# /abc/def/.htaccess -- per-dir config file for directory /abc/def
# Remember: /abc/def is the physical path of /xyz, i.e. the server
# has a 'Alias /xyz /abc/def' directive e.g.
#
RewriteEngine On
# let the server know that we are reached via /xyz and not
# via the physical path prefix /abc/def
RewriteBase /xyz
# now the rewriting rules
RewriteRule ^oldstuff\.html$ newstuff.html
</pre></td></tr>
</table>
<p>
In the above example, a request to <tt>/xyz/oldstuff.html</tt> gets correctly
rewritten to the physical file <tt>/abc/def/newstuff.html</tt>.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
<font size=-1>
<b>For the Apache hackers:</b><br>
The following list gives detailed information about the internal
processing steps:
<p>
<pre>
Request:
/xyz/oldstuff.html
Internal Processing:
/xyz/oldstuff.html -> /abc/def/oldstuff.html (per-server Alias)
/abc/def/oldstuff.html -> /abc/def/newstuff.html (per-dir RewriteRule)
/abc/def/newstuff.html -> /xyz/newstuff.html (per-dir RewriteBase)
/xyz/newstuff.html -> /abc/def/newstuff.html (per-server Alias)
Result:
/abc/def/newstuff.html
</pre>
This seems very complicated but is the correct Apache internal processing,
because the per-directory rewriting comes too late in the process. So,
when it occurs the (rewritten) request has to be re-injected into the Apache
kernel! BUT: While this seems like a serious overhead, it really isn't, because
this re-injection happens fully internal to the Apache server and the same
procedure is used by many other operations inside Apache. So, you can be
sure the design and implementation is correct.
</font>
</td></tr>
</table>
</blockquote>
<p>
<hr noshade size=1>
<p>
<a name="RewriteCond"><h3>RewriteCond</h3></a>
<strong>Syntax:</strong> <code>RewriteCond</code> <em>TestString</em> <em>CondPattern</em><br>
<strong>Default:</strong> -<em>None</em>-<br>
<strong>Context:</strong> server config, virtual host, per-directory config<br>
<p>
The <tt>RewriteCond</tt> directive defines a rule condition. Precede a
<tt>RewriteRule</tt> directive with one or more <t>RewriteCond</tt>
directives.
The following rewriting rule is only used if its pattern matches the current
state of the URI <b>AND</b> if these additional conditions apply, too.
<p>
<em>TestString</em> is a string which contains server-variables of the form
<blockquote><strong>
<tt>%{</tt> <em>NAME_OF_VARIABLE</em> <tt>}</tt>
</strong></blockquote>
where <em>NAME_OF_VARIABLE</em> can be a string
of the following list:
<p>
<table bgcolor="#d0d0d0" cellspacing=0 cellpadding=5>
<tr>
<td valign=top>
<b>HTTP headers:</b><p>
<font size=-1>
HTTP_USER_AGENT<br>
HTTP_REFERER<br>
HTTP_COOKIE<br>
HTTP_FORWARDED<br>
HTTP_HOST<br>
HTTP_PROXY_CONNECTION<br>
HTTP_ACCEPT<br>
</font>
</td>
<td valign=top>
<b>connection & request:</b><p>
<font size=-1>
REMOTE_ADDR<br>
REMOTE_HOST<br>
REMOTE_USER<br>
REMOTE_IDENT<br>
REQUEST_METHOD<br>
SCRIPT_FILENAME<br>
PATH_INFO<br>
QUERY_STRING<br>
AUTH_TYPE<br>
</font>
</td>
</tr>
<tr>
<td valign=top>
<b>server internals:</b><p>
<font size=-1>
DOCUMENT_ROOT<br>
SERVER_ADMIN<br>
SERVER_NAME<br>
SERVER_PORT<br>
SERVER_PROTOCOL<br>
SERVER_SOFTWARE<br>
SERVER_VERSION<br>
</font>
</td>
<td valign=top>
<b>system stuff:</b><p>
<font size=-1>
TIME_YEAR<br>
TIME_MON<br>
TIME_DAY<br>
TIME_HOUR<br>
TIME_MIN<br>
TIME_SEC<br>
TIME_WDAY<br>
</font>
</td>
<td valign=top>
<b>specials:</b><p>
<font size=-1>
API_VERSION<br>
THE_REQUEST<br>
REQUEST_URI<br>
REQUEST_FILENAME<br>
IS_SUBREQ<br>
</font>
</td>
</tr>
</table>
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
These variables all correspond to the similar named HTTP MIME-headers, C
variables of the Apache server or <tt>struct tm</tt> fields of the Unix
system.
</td></tr>
</table>
<p>
Special Notes:
<ol>
<li>The variables SCRIPT_FILENAME and REQUEST_FILENAME contain the same
value, i.e. the value of the <tt>filename</tt> field of the internal
<tt>request_rec</tt> structure of the Apache server. The first name is just the
commonly known CGI variable name while the second is the consistent
counterpart to REQUEST_URI (which contains the value of the <tt>uri</tt>
field of <tt>request_rec</tt>).
<p>
<li>There is the special format: <tt>%{ENV:variable}</tt> where
<i>variable</i> can be any environment variable. This is looked-up via
internal Apache structures and (if not found there) via <tt>getenv()</tt> from
the Apache server process.
<p>
<li>There is the special format: <tt>%{HTTP:header}</tt> where
<i>header</i> can be any HTTP MIME-header name. This is looked-up
from the HTTP request. Example: <tt>%{HTTP:Proxy-Connection}</tt>
is the value of the HTTP header ``<tt>Proxy-Connection:</tt>''.
<p>
<li>There is the special format: <tt>%{LA-U:url}</tt>
for look-aheads like <tt>-U</tt>. This performs a internal sub-request to
look-ahead for the final value of <i>url</i>.
<p>
<li>There is the special format: <tt>%{LA-F:file}</tt>
for look-aheads like <tt>-F</tt>. This performs a internal sub-request to
look-ahead for the final value of <i>file</i>.
</ol>
<p>
<em>CondPattern</em> is the condition pattern, i.e. a regular expression
which gets applied to the current instance of the <em>TestString</em>, i.e.
<em>TestString</em> gets evaluated and then matched against
<em>CondPattern</em>.
<p>
<b>Remember:</b> <em>CondPattern</em> is a standard
<em>Extended Regular Expression</em> with some additions:
<ol>
<li>You can precede the pattern string with a '<tt>!</tt>' character
(exclamation mark) to specify a <b>non</b>-matching pattern.
<p>
<li>
There are some special variants of <em>CondPatterns</em>. Instead of real
regular expression strings you can also use one of the following:
<p>
<ul>
<li>'<b>-d</b>' (is <b>d</b>irectory)<br>
Treats the <i>TestString</i> as a pathname and
tests if it exists and is a directory.
<p>
<li>'<b>-f</b>' (is regular <b>f</b>ile)<br>
Treats the <i>TestString</i> as a pathname and
tests if it exists and is a regular file.
<p>
<li>'<b>-s</b>' (is regular file with <b>s</b>ize)<br>
Treats the <i>TestString</i> as a pathname and
tests if it exists and is a regular file with size greater then zero.
<p>
<li>'<b>-l</b>' (is symbolic <b>l</b>ink)<br>
Treats the <i>TestString</i> as a pathname and
tests if it exists and is a symbolic link.
<p>
<li>'<b>-F</b>' (is existing file via subrequest)<br>
Checks if <i>TestString</i> is a valid file and accessible via all the
server's currently-configured access controls for that path. This uses an
internal subrequest to determine the check, so use it with care because it
decreases your servers performance!
<p>
<li>'<b>-U</b>' (is existing URL via subrequest)<br>
Checks if <i>TestString</i> is a valid URL and accessible via all the server's
currently-configured access controls for that path. This uses an internal
subrequest to determine the check, so use it with care because it decreases
your servers performance!
</ul>
<p>
Notice: All of these tests can also be prefixed by a not ('!') character
to negate their meaning.
</ol>
<p>
Additionally you can set special flags for <em>CondPattern</em> by appending
<blockquote><strong>
<code>[</code><em>flags</em><code>]</code>
</strong></blockquote>
as the third argument to the <tt>RewriteCond</tt> directive. <em>Flags</em>
is a comma-separated list of the following flags:
<ul>
<li>'<strong><code>nocase|NC</code></strong>' (<b>n</b>o <b>c</b>ase)<br>
This makes the condition test case-insensitive, i.e. there is
no difference between 'A-Z' and 'a-z' both in the expanded
<em>TestString</em> and the <em>CondPattern</em>.
<p>
<li>'<strong><code>ornext|OR</code></strong>' (<b>or</b> next condition)<br>
Use this to combine rule conditions with a local OR instead of the
implicit AND. Typical example:
<p>
<blockquote><pre>
RewriteCond %{REMOTE_HOST} ^host1.* [OR]
RewriteCond %{REMOTE_HOST} ^host2.* [OR]
RewriteCond %{REMOTE_HOST} ^host3.*
RewriteRule ...some special stuff for any of these hosts...
</pre></blockquote>
Without this flag you had to write down the cond/rule three times.
<p>
</ul>
<p>
<b>Example:</b>
<blockquote>
To rewrite the Homepage of a site according to the ``<tt>User-Agent:</tt>''
header of the request, you can use the following:
<blockquote><pre>
RewriteCond %{HTTP_USER_AGENT} ^Mozilla.*
RewriteRule ^/$ /homepage.max.html [L]
RewriteCond %{HTTP_USER_AGENT} ^Lynx.*
RewriteRule ^/$ /homepage.min.html [L]
RewriteRule ^/$ /homepage.std.html [L]
</pre></blockquote>
Interpretation: If you use Netscape Navigator as your browser (which identifies
itself as 'Mozilla'), then you get the max homepage, which includes
Frames, etc. If you use the Lynx browser (which is Terminal-based), then you
get the min homepage, which contains no images, no tables, etc. If you
use any other browser you get the standard homepage.
</blockquote>
<p>
<p>
<hr noshade size=1>
<p>
<a name="RewriteRule"><h3>RewriteRule</h3></a>
<strong>Syntax:</strong> <code>RewriteRule</code> <em>Pattern</em> <em>Substitution</em><br>
<strong>Default:</strong> -<em>None</em>-<br>
<strong>Context:</strong> server config, virtual host, per-directory config<br>
<p>
The <tt>RewriteRule</tt> directive is the real rewriting workhorse. The
directive can occur more than once. Each directive then defines one single
rewriting rule. The <b>definition order</b> of these rules is
<b>important</b>, because this order is used when applying the rules at
run-time.
<p>
<a name="patterns"><em>Pattern</em></a> can be (for Apache 1.1.x a System
V8 and for Apache 1.2.x a POSIX) <a name="regexp">regular expression</a>
which gets applied to the current URL. Here ``current'' means the value of the
URL when this rule gets applied. This may not be the original requested
URL, because there could be any number of rules before which already matched
and made alterations to it.
<p>
Some hints about the syntax of regular expressions:
<p>
<table bgcolor="#d0d0d0" cellspacing=0 cellpadding=5>
<tr>
<td valign=top>
<pre>
<strong><code>^</code></strong> Start of line
<strong><code>$</code></strong> End of line
<strong><code>.</code></strong> Any single character
<strong><code>[</code></strong>chars<strong><code>]</code></strong> One of chars
<strong><code>[^</code></strong>chars<strong><code>]</code></strong> None of chars
<strong><code>?</code></strong> 0 or 1 of the preceding char
<strong><code>*</code></strong> 0 or N of the preceding char
<strong><code>+</code></strong> 1 or N of the preceding char
<strong><code>\</code></strong>char escape that specific char
(e.g. for specifying the chars "<code>.[]()</code>" etc.)
<strong><code>(</code></strong>string<strong><code>)</code></strong> Grouping of chars (the <b>N</b>th group can be used on the RHS with <code>$</code><b>N</b>)
</pre>
</td>
</tr>
</table>
<p>
Additionally the NOT character ('<tt>!</tt>') is a possible pattern
prefix. This gives you the ability to negate a pattern; to say, for instance: ``<i>if
the current URL does <b>NOT</b> match to this pattern</i>''. This can be used
for special cases where it is better to match the negative pattern or as a
last default rule.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
<b>Notice!</b> When using the NOT character to negate a pattern you cannot
have grouped wildcard parts in the pattern. This is impossible because when
the pattern does NOT match, there are no contents for the groups. In
consequence, if negated patterns are used, you cannot use <tt>$N</tt> in the
substitution string!
</td></tr>
</table>
<p>
<a name="rhs"><em>Substitution</em></a> of a rewriting rule is the string
which is substituted for (or replaces) the original URL for which
<em>Pattern</em> matched. Beside plain text you can use
<ol>
<li>pattern-group back-references (<code>$N</code>)
<li>server-variables as in rule condition test-strings (<code>%{VARNAME}</code>)
<li><a href="#mapfunc">mapping-function</a> calls (<code>${mapname:key|default}</code>)
</ol>
Back-references are <code>$</code><b>N</b> (<b>N</b>=1..9) identifiers which
will be replaced by the contents of the <b>N</b>th group of the matched
<em>Pattern</em>. The server-variables are the same as for the
<em>TestString</em> of a <tt>RewriteCond</tt> directive. The
mapping-functions come from the <tt>RewriteMap</tt> directive and are
explained there. These three types of variables are expanded in the order of
the above list.
<p>
As already mentioned above, all the rewriting rules are applied to the
<em>Substitution</em> (in the order of definition in the config file). The
URL is <b>completely replaced</b> by the <em>Substitution</em> and the
rewriting process goes on until there are no more rules (unless explicitly
terminated by a <code><b>L</b></code> flag - see below).
<p>
There is a special substitution string named '<tt>-</tt>' which means:
<b>NO substitution</b>! Sounds silly? No, it is useful to provide rewriting
rules which <b>only</b> match some URLs but do no substitution, e.g. in
conjunction with the <b>C</b> (chain) flag to be able to have more than one
pattern to be applied before a substitution occurs.
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
<b>Notice</b>: There is a special feature. When you prefix a substitution
field with <tt>http://</tt><em>thishost</em>[<em>:thisport</em>] then
<b>mod_rewrite</b> automatically strips it out. This auto-reduction on
implicit external redirect URLs is a useful and important feature when
used in combination with a mapping-function which generates the hostname
part. Have a look at the first example in the example section below to
understand this.
<p>
<b>Remember:</b> An unconditional external redirect to your own server will
not work with the prefix <tt>http://thishost</tt> because of this feature.
To achieve such a self-redirect, you have to use the <b>R</b>-flag (see
below).
</td></tr>
</table>
<p>
Additionally you can set special flags for <em>Substitution</em> by appending
<blockquote><strong>
<code>[</code><em>flags</em><code>]</code>
</strong></blockquote>
as the third argument to the <tt>RewriteRule</tt> directive. <em>Flags</em> is a
comma-separated list of the following flags:
<ul>
<li>'<strong><code>redirect|R</code>[=<i>code</i>]</strong>' (force <a name="redirect"><b>r</b>edirect</a>)<br>
Prefix <em>Substitution</em>
with <code>http://thishost[:thisport]/</code> (which makes the new URL a URI) to
force a external redirection. If no <i>code</i> is given a HTTP response
of 302 (MOVED TEMPORARILY) is used. If you want to use other response
codes in the range 300-400 just specify them as a number or use
one of the following symbolic names: <tt>temp</tt> (default), <tt>permanent</tt>,
<tt>seeother</tt>.
Use it for rules which should
canonicalize the URL and gives it back to the client, e.g. translate
``<code>/~</code>'' into ``<code>/u/</code>'' or always append a slash to
<code>/u/</code><em>user</em>, etc.<br>
<p>
<b>Notice:</b> When you use this flag, make sure that the
substitution field is a valid URL! If not, you are redirecting to an
invalid location! And remember that this flag itself only prefixes the
URL with <code>http://thishost[:thisport]/</code>, but rewriting goes on.
Usually you also want to stop and do the redirection immediately. To stop
the rewriting you also have to provide the 'L' flag.
<p>
<li>'<strong><code>forbidden|F</code></strong>' (force URL to be <b>f</b>orbidden)<br>
This forces the current URL to be forbidden, i.e. it immediately sends
back a HTTP response of 403 (FORBIDDEN). Use this flag in conjunction with
appropriate RewriteConds to conditionally block some URLs.
<p>
<li>'<strong><code>gone|G</code></strong>' (force URL to be <b>g</b>one)<br>
This forces the current URL to be gone, i.e. it immediately sends back a
HTTP response of 410 (GONE). Use this flag to mark no longer existing
pages as gone.
<p>
<li>'<strong><code>proxy|P</code></strong>' (force <b>p</b>roxy)<br>
This flag forces the substitution part to be internally forced as a proxy
request and immediately (i.e. rewriting rule processing stops here) put
through the proxy module. You have to make sure that the substitution
string is a valid URI (e.g. typically <tt>http://</tt>) which can
be handled by the Apache proxy module. If not you get an error from
the proxy module. Use this flag to achieve a more powerful implementation
of the <tt>mod_proxy</tt> directive <tt>ProxyPass</tt>, to map
some remote stuff into the namespace of the local server.
<p>
Notice: <b>You really have to put <tt>ProxyRequests On</tt> into your
server configuration to prevent proxy requests from leading to core-dumps
inside the Apache kernel. If you have not compiled in the proxy module,
then there is no core-dump problem, because mod_rewrite checks for
existence of the proxy module and if lost forbids proxy URLs. </b>
<p>
<li>'<strong><code>last|L</code></strong>' (<b>l</b>ast rule)<br>
Stop the rewriting process here and
don't apply any more rewriting rules. This corresponds to the Perl
<code>last</code> command or the <code>break</code> command from the C
language. Use this flag to prevent the currently rewritten URL from being
rewritten further by following rules which may be wrong. For
example, use it to rewrite the root-path URL ('<code>/</code>') to a real
one, e.g. '<code>/e/www/</code>'.
<p>
<li>'<strong><code>next|N</code></strong>' (<b>n</b>ext round)<br>
Re-run the rewriting process (starting again with the first rewriting
rule). Here the URL to match is again not the original URL but the URL
from the last rewriting rule. This corresponds to the Perl
<code>next</code> command or the <code>continue</code> command from the C
language. Use this flag to restart the rewriting process, i.e. to
immediately go to the top of the loop. <br>
<b>But be careful not to create a deadloop!</b>
<p>
<li>'<strong><code>chain|C</code></strong>' (<b>c</b>hained with next rule)<br>
This flag chains the current rule with the next rule (which itself can
also be chained with its following rule, etc.). This has the following
effect: if a rule matches, then processing continues as usual, i.e. the
flag has no effect. If the rule does <b>not</b> match, then all following
chained rules are skipped. For instance, use it to remove the
``<tt>.www</tt>'' part inside a per-directory rule set when you let an
external redirect happen (where the ``<tt>.www</tt>'' part should not to
occur!).
<p>
<li>'<strong><code>type|T</code></strong>=<em>mime-type</em>' (force MIME <b>t</b>ype)<br>
Force the MIME-type of the target file to be <em>mime-type</em>. For
instance, this can be used to simulate the old <tt>mod_alias</tt>
directive <tt>ScriptAlias</tt> which internally forces all files inside
the mapped directory to have a MIME type of
``<tt>application/x-httpd-cgi</tt>''.
<p>
<li>'<strong><code>nosubreq|NS</code></strong>' (used only if <b>n</b>o internal <b>s</b>ub-request)<br>
This flag forces the rewriting engine to skip a rewriting rule if the
current request is an internal sub-request. For instance, sub-requests
occur internally in Apache when <tt>mod_include</tt> tries to find out
information about possible directory default files (<tt>index.xxx</tt>).
On sub-requests it is not always useful and even sometimes causes a failure to
if the complete set of rules are applied. Use this flag to exclude some rules.<br>
<p>
Use the following rule for your decision: whenever you prefix some URLs
with CGI-scripts to force them to be processed by the CGI-script, the
chance is high that you will run into problems (or even overhead) on sub-requests.
In these cases, use this flag.
<p>
<li>'<strong><code>passthrough|PT</code></strong>' (<b>p</b>ass <b>t</b>hrough to next handler)<br>
This flag forces the rewriting engine to set the <code>uri</code> field
of the internal <code>request_rec</code> structure to the value
of the <code>filename</code> field. This flag is just a hack to be able
to post-process the output of <tt>RewriteRule</tt> directives by
<tt>Alias</tt>, <tt>ScriptAlias</tt>, <tt>Redirect</tt>, etc. directives
from other URI-to-filename translators. A trivial example to show the
semantics:
If you want to rewrite <tt>/abc</tt> to <tt>/def</tt> via the rewriting
engine of <tt>mod_rewrite</tt> and then <tt>/def</tt> to <tt>/ghi</tt>
with <tt>mod_alias</tt>:
<pre>
RewriteRule ^/abc(.*) /def$1 [PT]
Alias /def /ghi
</pre>
If you omit the <tt>PT</tt> flag then <tt>mod_rewrite</tt>
will do its job fine, i.e. it rewrites <tt>uri=/abc/...</tt> to
<tt>filename=/def/...</tt> as a full API-compliant URI-to-filename
translator should do. Then <tt>mod_alias</tt> comes and tries to do a
URI-to-filename transition which will not work.
<p>
Notice: <b>You have to use this flag if you want to intermix directives
of different modules which contain URL-to-filename translators</b>. The
typical example is the use of <tt>mod_alias</tt> and
<tt>mod_rewrite</tt>..
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
<font size=-1>
<b>For the Apache hackers:</b><br>
If the current Apache API had a
filename-to-filename hook additionally to the URI-to-filename hook then
we wouldn't need this flag! But without such a hook this flag is the
only solution. The Apache Group has discussed this problem and will
add such hooks into Apache version 2.0.
</font>
</td></tr>
</table>
<p>
<li>'<strong><code>skip|S</code></strong>=<em>num</em>' (<b>s</b>kip next rule(s))<br>
This flag forces the rewriting engine to skip the next <em>num</em> rules
in sequence when the current rule matches. Use this to make pseudo
if-then-else constructs: The last rule of the then-clause becomes
a <tt>skip=N</tt> where N is the number of rules in the else-clause.
(This is <b>not</b> the same as the 'chain|C' flag!)
<p>
<li>'<strong><code>env|E=</code></strong><i>VAR</i>:<i>VAL</i>' (set <b>e</b>nvironment variable)<br>
This forces an environment variable named <i>VAR</i> to be set to the value
<i>VAL</i>, where <i>VAL</i> can contain regexp backreferences <tt>$N</tt>
which will be expanded. You can use this flag more than once to set more
than one variable. The variables can be later dereferenced at a lot of
situations, but the usual location will be from within XSSI (via
<tt><!--#echo var="VAR"--></tt>) or CGI (e.g. <tt>$ENV{'VAR'}</tt>).
But additionally you can also dereference it in a following RewriteCond
pattern via <tt>%{ENV:VAR}</tt>. Use this to strip but remember
information from URLs.
</ul>
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
Remember: Never forget that <em>Pattern</em> gets applied to a complete URL
in per-server configuration files. <b>But in per-directory configuration
files, the per-directory prefix (which always is the same for a specific
directory!) gets automatically <em>removed</em> for the pattern matching and
automatically <em>added</em> after the substitution has been done.</b> This feature is
essential for many sorts of rewriting, because without this prefix stripping
you have to match the parent directory which is not always possible.
<p>
There is one exception: If a substitution string starts with
``<tt>http://</tt>'' then the directory prefix will be <b>not</b> added and a
external redirect or proxy throughput (if flag <b>P</b> is used!) is forced!
</td></tr>
</table>
<p>
<table width=70% border=2 bgcolor="#c0c0e0" cellspacing=0 cellpadding=10>
<tr><td>
Notice! To enable the rewriting engine for per-directory configuration files
you need to set ``<tt>RewriteEngine On</tt>'' in these files <b>and</b>
``<tt>Option FollowSymLinks</tt>'' enabled. If your administrator has
disabled override of <tt>FollowSymLinks</tt> for a user's directory, then
you cannot use the rewriting engine. This restriction is needed for
security reasons.
</td></tr>
</table>
<p>
Here are all possible substitution combinations and their meanings:
<p>
<b>Inside per-server configuration (<tt>httpd.conf</tt>)<br>
for request ``<tt>GET /somepath/pathinfo</tt>'':</b><br>
<p>
<table bgcolor="#d0d0d0" cellspacing=0 cellpadding=5>
<tr>
<td>
<pre>
<b>Given Rule</b> <b>Resulting Substitution</b>
---------------------------------------------- ----------------------------------
^/somepath(.*) otherpath$1 not supported, because invalid!
^/somepath(.*) otherpath$1 [R] not supported, because invalid!
^/somepath(.*) otherpath$1 [P] not supported, because invalid!
---------------------------------------------- ----------------------------------
^/somepath(.*) /otherpath$1 /otherpath/pathinfo
^/somepath(.*) /otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^/somepath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^/somepath(.*) http://thishost/otherpath$1 /otherpath/pathinfo
^/somepath(.*) http://thishost/otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^/somepath(.*) http://thishost/otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^/somepath(.*) http://otherhost/otherpath$1 http://otherhost/otherpath/pathinfo
via external redirection
^/somepath(.*) http://otherhost/otherpath$1 [R] http://otherhost/otherpath/pathinfo
via external redirection
(the [R] flag is redundant)
^/somepath(.*) http://otherhost/otherpath$1 [P] http://otherhost/otherpath/pathinfo
via internal proxy
</pre>
</td>
</tr>
</table>
<p>
<b>Inside per-directory configuration for <tt>/somepath</tt><br>
(i.e. file <tt>.htaccess</tt> in dir <tt>/physical/path/to/somepath</tt> containing
<tt>RewriteBase /somepath</tt>)<br> for
request ``<tt>GET /somepath/localpath/pathinfo</tt>'':</b><br>
<p>
<table bgcolor="#d0d0d0" cellspacing=0 cellpadding=5>
<tr>
<td>
<pre>
<b>Given Rule</b> <b>Resulting Substitution</b>
---------------------------------------------- ----------------------------------
^localpath(.*) otherpath$1 /somepath/otherpath/pathinfo
^localpath(.*) otherpath$1 [R] http://thishost/somepath/otherpath/pathinfo
via external redirection
^localpath(.*) otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^localpath(.*) /otherpath$1 /otherpath/pathinfo
^localpath(.*) /otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^localpath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^localpath(.*) http://thishost/otherpath$1 /otherpath/pathinfo
^localpath(.*) http://thishost/otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^localpath(.*) http://thishost/otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^localpath(.*) http://otherhost/otherpath$1 http://otherhost/otherpath/pathinfo
via external redirection
^localpath(.*) http://otherhost/otherpath$1 [R] http://otherhost/otherpath/pathinfo
via external redirection
(the [R] flag is redundant)
^localpath(.*) http://otherhost/otherpath$1 [P] http://otherhost/otherpath/pathinfo
via internal proxy
</pre>
</td>
</tr>
</table>
</td>
</tr>
</table>
<p>
<b>Example:</b>
<p>
<blockquote>
We want to rewrite URLs of the form
<blockquote>
<code>/</code> <em>Language</em>
<code>/~</code> <em>Realname</em>
<code>/.../</code> <em>File</em>
</blockquote>
into
<blockquote>
<code>/u/</code> <em>Username</em>
<code>/.../</code> <em>File</em>
<code>.</code> <em>Language</em>
</blockquote>
<p>
We take the rewrite mapfile from above and save it under
<code>/anywhere/map.real-to-user</code>. Then we only have to add the
following lines to the Apache server configuration file:
<blockquote>
<pre>
RewriteLog /anywhere/rewrite.log
RewriteMap real-to-user txt:/anywhere/map.real-to-host
RewriteRule ^/([^/]+)/~([^/]+)/(.*)$ /u/${real-to-user:$2|nobody}/$3.$1
</pre>
</blockquote>
</blockquote>
<!--#include virtual="footer.html" -->
</BODY>
</HTML>
<!--/%hypertext -->
|
