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| − | ==NAME==
| + | {{RetroCDN}} |
| − | patch - apply a diff file to an original | + | A '''patch''' is a file or set of files that is used to modify another file or set of files. It may be distributed as either a standalone program, or a data file which requires a specialised program to apply the patch. |
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| − | ==SYNOPSIS== | + | ==ROM patches== |
| − | '''patch''' [''options''] [''originalfile'' [''patchfile'']]
| + | The hacking scene has seen several types of patches, including [[IPS]] and [[RXL]], used for [[ROM hack]]s. Both these types of patch require programs (for example [[StealthPatch]]) to modify the target file. Patches were used during a time when downloading full ROMs would be a lengthy task for slow Internet connections, but with the advent of high-speed Internet connections, patches have fallen into disuse as Sonic-game hackers have made fully modified ROMs available. |
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| − | but usually just
| + | ROM patches are still utilized (and often, required) by other communities, due to precautions related to copyright. |
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| − | '''patch''' -p''num'' <''patchfile''
| + | ==Software patches== |
| | + | More complicated games and programs require more complicated patches. Most installed games consist of many files and folders, so something as simple as an IPS patch would be inappropriate. In these cases, standalone programs are used to modify or replace several files automatically. If a game has a fault which was not detected in the [[beta]] testing phase, the developer will typically distribute a patch to correct it. |
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| − | ==DESCRIPTION==
| + | [[Category:Technical information]] |
| − | '''patch''' takes a patch file ''patchfile'' containing a difference listing produced by the '''diff''' program and applies those differences to one or more original files, producing patched versions. Normally the patched versions are put in place of the originals. Backups can be made; see the '''-b''' or '''--backup option'''. The names of the files to be patched are usually taken from the patch file, but if there’s just one file to be patched it can specified on the command line as ''originalfile''.
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| − | Upon startup, patch attempts to determine the type of the diff listing, unless overruled by a '''-c''' ('''--context'''), '''-e''' ('''--ed'''), '''-n''' ('''--normal'''), or '''-u''' ('''--unified''') option. Context diffs (old-style, new-style, and unified) and normal diffs are applied by the '''patch''' program itself, while '''ed''' diffs are simply fed to the '''ed'''(1) editor via a pipe.
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| − | '''patch''' tries to skip any leading garbage, apply the diff, and then skip any trailing garbage. Thus you could feed an article or message containing a diff listing to '''patch''', and it should work. If the entire diff is indented by a consistent amount, or if a context diff contains lines ending in CRLF or is encapsulated one or more times by prepending "'''-''' " to lines starting with "'''-'''" as specified by Internet RFC 934, this is taken into account.
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| − | With context diffs, and to a lesser extent with normal diffs, '''patch''' can detect when the line numbers mentioned in the patch are incorrect, and attempts to find the correct place to apply each hunk of the patch. As a first guess, it takes the line number mentioned for the hunk, plus or minus any offset used in applying the previous hunk. If that is not the correct place, '''patch''' scans both forwards and backwards for a set of lines matching the context given in the hunk. First '''patch''' looks for a place where all lines of the context match. If no such place is found, and it’s a context diff, and the maximum fuzz factor is set to 1 or more, then another scan takes place ignoring the first and last line of context. If that fails, and the maximum fuzz factor is set to 2 or more, the first two and last two lines of context are ignored, and another scan is made. (The default maximum fuzz factor is 2.) If '''patch''' cannot find a place to install that hunk of the patch, it puts the hunk out to a reject file, which normally is the name of the output file plus a '''.rej''' suffix, or '''#''' if '''.rej''' would generate a file name that is too long (if even appending the single character '''#''' makes the file name too long, then '''#''' replaces the file name’s last character). (The rejected hunk comes out in ordinary context diff form regardless of the input patch’s form. If the input was a normal diff, many of the contexts are simply null.) The line numbers on the hunks in the reject file may be different than in the patch file: they reflect the approximate location patch thinks the failed hunks belong in the new file rather than the old one.
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| − | As each hunk is completed, you are told if the hunk failed, and if so which line (in the new file) '''patch''' thought the hunk should go on. If the hunk is installed at a different line from the line number specified in the diff you are told the offset. A single large offset may indicate that a hunk was installed in the wrong place. You are also told if a fuzz factor was used to make the match, in which case you should also be slightly suspicious. If the '''--verbose''' option is given, you are also told about hunks that match exactly.
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| − | If no original file ''origfile'' is specified on the command line, '''patch''' tries to figure out from the leading garbage what the name of the file to edit is, using the following rules.
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| − | First, '''patch''' takes an ordered list of candidate file names as follows:
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| − | * If the header is that of a context diff, '''patch''' takes the old and new file names in the header. A name is ignored if it does not have enough slashes to satisfy the '''-p'''''num'' or '''--strip='''''num'' option. The name '''/dev/null''' is also ignored.
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A patch is a file or set of files that is used to modify another file or set of files. It may be distributed as either a standalone program, or a data file which requires a specialised program to apply the patch.
ROM patches
The hacking scene has seen several types of patches, including IPS and RXL, used for ROM hacks. Both these types of patch require programs (for example StealthPatch) to modify the target file. Patches were used during a time when downloading full ROMs would be a lengthy task for slow Internet connections, but with the advent of high-speed Internet connections, patches have fallen into disuse as Sonic-game hackers have made fully modified ROMs available.
ROM patches are still utilized (and often, required) by other communities, due to precautions related to copyright.
Software patches
More complicated games and programs require more complicated patches. Most installed games consist of many files and folders, so something as simple as an IPS patch would be inappropriate. In these cases, standalone programs are used to modify or replace several files automatically. If a game has a fault which was not detected in the beta testing phase, the developer will typically distribute a patch to correct it.
