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GNU Info File | 1993-05-19 | 50KB | 954 lines

This is Info file diff.info, produced by Makeinfo-1.54 from the input file ./diff.texi. This file documents the the GNU `diff', `diff3', `sdiff', and `cmp' commands for showing the differences between text files and the `patch' command for using their output to update files. Copyright (C) 1992, 1993 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. File: diff.info, Node: Line Formats, Next: Detailed If-then-else, Prev: Line Group Formats, Up: If-then-else Line Formats ------------ Line formats control how each line taken from an input file is output as part of a line group in if-then-else format. For example, the following command outputs text with a one-column change indicator to the left of the text. The first column of output is `-' for deleted lines, `|' for added lines, and a space for unchanged lines. The formats contain newline characters where newlines are desired on output. diff \ --old-line-format='-%l ' \ --new-line-format='|%l ' \ --unchanged-line-format=' %l ' \ old new To specify a line format, use one of the following options. You should quote FORMAT, since it often contains shell metacharacters. `--old-line-format=FORMAT' formats lines just from the first file. `--new-line-format=FORMAT' formats lines just from the second file. `--unchanged-line-format=FORMAT' formats lines common to both files. In a line format, ordinary characters represent themselves; conversion specifications start with `%' and have one of the following forms. stands for the the contents of the line, not counting its trailing newline (if any). This format ignores whether the line is incomplete; *Note Incomplete Lines::. stands for the the contents of the line, including its trailing newline (if any). If a line is incomplete, this format preserves its incompleteness. stands for a null character. stands for `%'. The default line format is `%l' followed by a newline character. If the input contains tab characters and it is important that they line up on output, you should ensure that `%l' or `%L' in a line format is just after a tab stop (e.g. by preceding `%l' or `%L' with a tab character), or you should use the `-t' or `--expand-tabs' option. File: diff.info, Node: Detailed If-then-else, Next: Example If-then-else, Prev: Line Formats, Up: If-then-else Detailed Description of If-then-else Format ------------------------------------------- For lines common to both files, `diff' uses the unchanged line group format. For each hunk of differences in the merged output format, if the hunk contains only lines from the first file, `diff' uses the old line group format; if the hunk contains only lines from the second file, `diff' uses the new group format; otherwise, `diff' uses the changed group format. The old, new, and unchanged line formats specify the output format of lines from the first file, lines from the second file, and lines common to both files, respectively. The option `--ifdef=NAME' is equivalent to the following sequence of options using shell syntax: --old-group-format='#ifndef NAME %<#endif /* not NAME */ ' \ --new-group-format='#ifdef NAME %>#endif /* NAME */ ' \ --unchanged-group-format='%=' \ --changed-group-format='#ifndef NAME %<#else /* NAME */ %>#endif /* NAME */ ' You should carefully check the `diff' output for proper nesting. For example, when using the the `-D NAME' or `--ifdef=NAME' option, you should check that if the differing lines contain any of the C preprocessor directives `#ifdef', `#ifndef', `#else', `#elif', or `#endif', they are nested properly and match. If they don't, you must make corrections manually. It is a good idea to carefully check the resulting code anyway to make sure that it really does what you want it to; depending on how the input files were produced, the output might contain duplicate or otherwise incorrect code. The `patch' `-D NAME' option behaves just like the `diff' `-D NAME' option, except it operates on a file and a diff to produce a merged file; *Note patch Options::. File: diff.info, Node: Example If-then-else, Prev: Detailed If-then-else, Up: If-then-else An Example of If-then-else Format --------------------------------- Here is the output of `diff -DTWO lao tzu' (*note Sample diff Input::., for the complete contents of the two files): #ifndef TWO The Way that can be told of is not the eternal Way; The name that can be named is not the eternal name. #endif /* not TWO */ The Nameless is the origin of Heaven and Earth; #ifndef TWO The Named is the mother of all things. #else /* TWO */ The named is the mother of all things. #endif /* TWO */ Therefore let there always be non-being, so we may see their subtlety, And let there always be being, so we may see their outcome. The two are the same, But after they are produced, they have different names. #ifdef TWO They both may be called deep and profound. Deeper and more profound, The door of all subtleties! #endif /* TWO */ File: diff.info, Node: Comparing Directories, Next: Adjusting Output, Prev: Output Formats, Up: Top Comparing Directories ********************* You can use `diff' to compare some or all of the files in two directory trees. When both file name arguments to `diff' are directories, it compares each file that is contained in both directories, examining file names in alphabetical order. Normally `diff' is silent about pairs of files that contain no differences, but if you use the `-s' or `--report-identical-files' option, it reports pairs of identical files. Normally `diff' reports subdirectories common to both directories without comparing subdirectories' files, but if you use the `-r' or `--recursive' option, it compares every corresponding pair of files in the directory trees, as many levels deep as they go. For file names that are in only one of the directories, `diff' normally does not show the contents of the file that exists; it reports only that the file exists in that directory and not in the other. You can make `diff' act as though the file existed but was empty in the other directory, so that it outputs the entire contents of the file that actually exists. (It is output as either an insertion or a deletion, depending on whether it is in the first or the second directory given.) To do this, use the `-N' or `--new-file' option. If the older directory contains one or more large files that are not in the newer directory, you can make the patch smaller by using the `-P' or `--unidirectional-new-file' option instead of `-N'. This option is like `-N' except that it only inserts the contents of files that appear in the second directory but not the first (that is, files that were added). At the top of the patch, write instructions for the user applying the patch to remove the files that were deleted before applying the patch. *Note Making Patches::, for more discussion of making patches for distribution. To ignore some files while comparing directories, use the `-x PATTERN' or `--exclude=PATTERN' option. This option ignores any files or subdirectories whose base names match the shell pattern PATTERN. Unlike in the shell, a period at the start of the base of a file name matches a wildcard at the start of a pattern. You should enclose PATTERN in quotes so that the shell does not expand it. For example, the option `-x '*.[ao]'' ignores any file whose name ends with `.a' or `.o'. This option accumulates if you specify it more than once. For example, using the options `-x 'RCS' -x '*,v'' ignores any file or subdirectory whose base name is `RCS' or ends with `,v'. If you need to give this option many times, you can instead put the patterns in a file, one pattern per line, and use the `-X FILE' or `--exclude-from=FILE' option. If you have been comparing two directories and stopped partway through, later you might want to continue where you left off. You can do this by using the `-S FILE' or `--starting-file=FILE' option. This compares only the file FILE and all alphabetically later files in the topmost directory level. File: diff.info, Node: Adjusting Output, Next: diff Performance, Prev: Comparing Directories, Up: Top Making `diff' Output Prettier ***************************** `diff' provides several ways to adjust the appearance of its output. These adjustments can be applied to any output format. * Menu: * Tabs:: Preserving the alignment of tabstops. * Pagination:: Page numbering and timestamping `diff' output. File: diff.info, Node: Tabs, Next: Pagination, Up: Adjusting Output Preserving Tabstop Alignment ============================ The lines of text in some of the `diff' output formats are preceded by one or two characters that indicate whether the text is inserted, deleted, or changed. The addition of those characters can cause tabs to move to the next tabstop, throwing off the alignment of columns in the line. GNU `diff' provides two ways to make tab-aligned columns line up correctly. The first way is to have `diff' convert all tabs into the correct number of spaces before outputting them; select this method with the `-t' or `--expand-tabs' option. `diff' assumes that tabstops are set every 8 columns. To use this form of output with `patch', you must give `patch' the `-l' or `--ignore-whitespace' option (*note Changed Whitespace::., for more information). The other method for making tabs line up correctly is to add a tab character instead of a space after the indicator character at the beginning of the line. This ensures that all following tab characters are in the same position relative to tabstops that they were in the original files, so that the output is aligned correctly. Its disadvantage is that it can make long lines too long to fit on one line of the screen or the paper. It also does not work with the unified output format, which does not have a space character after the change type indicator character. Select this method with the `-T' or `--initial-tab' option. File: diff.info, Node: Pagination, Prev: Tabs, Up: Adjusting Output Paginating `diff' Output ======================== It can be convenient to have long output page-numbered and time-stamped. The `-l' and `--paginate' options do this by sending the `diff' output through the `pr' program. Here is what the page header might look like for `diff -lc lao tzu': Mar 11 13:37 1991 diff -lc lao tzu Page 1 File: diff.info, Node: diff Performance, Next: Comparing Three Files, Prev: Adjusting Output, Up: Top `diff' Performance Tradeoffs **************************** GNU `diff' runs quite efficiently; however, in some circumstances you can cause it to run faster or produce a more compact set of changes. There are two ways that you can affect the performance of GNU `diff' by changing the way it compares files. Performance has more than one dimension. These options improve one aspect of performance at the cost of another, or they improve performance in some cases while hurting it in others. The way that GNU `diff' determines which lines have changed always comes up with a near-minimal set of differences. Usually it is good enough for practical purposes. If the `diff' output is large, you might want `diff' to use a modified algorithm that sometimes produces a smaller set of differences. The `-d' or `--minimal' option does this; however, it can also cause `diff' to run more slowly than usual, so it is not the default behavior. When the files you are comparing are large and have small groups of changes scattered throughout them, you can use the `-H' or `--speed-large-files' option to make a different modification to the algorithm that `diff' uses. If the input files have a constant small density of changes, this option speeds up the comparisons without changing the output. If not, `diff' might produce a larger set of differences; however, the output will still be correct. Normally `diff' discards the prefix and suffix that is common to both files before it attempts to find a minimal set of differences. This makes `diff' run faster, but occasionally it may produce non-minimal output. The `--horizon-lines=LINES' option prevents `diff' from discarding the last LINES lines of the prefix and the first LINES lines of the suffix. This gives `diff' further opportunities to find a minimal output. File: diff.info, Node: Comparing Three Files, Next: diff3 Merging, Prev: diff Performance, Up: Top Comparing Three Files ********************* Use the program `diff3' to compare three files and show any differences among them. (`diff3' can also merge files; see *Note diff3 Merging::). The "normal" `diff3' output format shows each hunk of differences without surrounding context. Hunks are labeled depending on whether they are two-way or three-way, and lines are annotated by their location in the input files. *Note Invoking diff3::, for more information on how to run `diff3'. * Menu: * Sample diff3 Input:: Sample `diff3' input for examples. * Detailed diff3 Normal:: A detailed description of normal output format. * diff3 Hunks:: The format of normal output format. * Example diff3 Normal:: Sample output in the normal format. File: diff.info, Node: Sample diff3 Input, Next: Detailed diff3 Normal, Up: Comparing Three Files A Third Sample Input File ========================= Here is a third sample file that will be used in examples to illustrate the output of `diff3' and how various options can change it. The first two files are the same that we used for `diff' (*note Sample diff Input::.). This is the third sample file, called `tao': The Way that can be told of is not the eternal Way; The name that can be named is not the eternal name. The Nameless is the origin of Heaven and Earth; The named is the mother of all things. Therefore let there always be non-being, so we may see their subtlety, And let there always be being, so we may see their result. The two are the same, But after they are produced, they have different names. -- The Way of Lao-Tzu, tr. Wing-tsit Chan File: diff.info, Node: Detailed diff3 Normal, Next: diff3 Hunks, Prev: Sample diff3 Input, Up: Comparing Three Files Detailed Description of `diff3' Normal Format ============================================= Each hunk begins with a line marked `===='. Three-way hunks have plain `====' lines, and two-way hunks have `1', `2', or `3' appended to specify which of the three input files differ in that hunk. The hunks contain copies of two or three sets of input lines each preceded by one or two commands identifying where the lines came from. Two spaces precede each copy of an input line to distinguish it from the commands. Commands take the following forms: `FILE:La' This hunk appears after line L of file FILE, and contains no lines in that file. To edit this file to yield the other files, one must append hunk lines taken from the other files. For example, `1:11a' means that the hunk follows line 11 in the first file and contains no lines from that file. `FILE:Rc' This hunk contains the lines in the range R of file FILE. The range R is a comma-separated pair of line numbers, or just one number if the range is a singleton. To edit this file to yield the other files, one must change the specified lines to be the lines taken from the other files. For example, `2:11,13c' means that the hunk contains lines 11 through 13 from the second file. If the last line in a set of input lines is incomplete (*note Incomplete Lines::.), it is distinguished on output from a full line by a following line that starts with `\'. File: diff.info, Node: diff3 Hunks, Next: Example diff3 Normal, Prev: Detailed diff3 Normal, Up: Comparing Three Files `diff3' Hunks ============= Groups of lines that differ in two or three of the input files are called "diff3 hunks", by analogy with `diff' hunks (*note Hunks::.). If all three input files differ in a `diff3' hunk, the hunk is called a "three-way hunk"; if just two input files differ, it is a "two-way hunk". As with `diff', several solutions are possible. When comparing the files `A', `B', and `C', `diff3' normally finds `diff3' hunks by merging the two-way hunks output by the two commands `diff A B' and `diff A C'. This does not necessarily minimize the size of the output, but exceptions should be rare. For example, suppose `F' contains the three lines `a', `b', `f', `G' contains the lines `g', `b', `g', and `H' contains the lines `a', `b', `h'. `diff3 F G H' might output the following: ====2 1:1c 3:1c a 2:1c g ==== 1:3c f 2:3c g 3:3c h because it found a two-way hunk containing `a' in the first and third files and `g' in the second file, then the single line `b' common to all three files, then a three-way hunk containing the last line of each file. File: diff.info, Node: Example diff3 Normal, Prev: diff3 Hunks, Up: Comparing Three Files An Example of `diff3' Normal Format =================================== Here is the output of the command `diff3 lao tzu tao' (*note Sample diff3 Input::., for the complete contents of the files). Notice that it shows only the lines that are different among the three files. ====2 1:1,2c 3:1,2c The Way that can be told of is not the eternal Way; The name that can be named is not the eternal name. 2:0a ====1 1:4c The Named is the mother of all things. 2:2,3c 3:4,5c The named is the mother of all things. ====3 1:8c 2:7c so we may see their outcome. 3:9c so we may see their result. ==== 1:11a 2:11,13c They both may be called deep and profound. Deeper and more profound, The door of all subtleties! 3:13,14c -- The Way of Lao-Tzu, tr. Wing-tsit Chan File: diff.info, Node: diff3 Merging, Next: Interactive Merging, Prev: Comparing Three Files, Up: Top Merging From a Common Ancestor ****************************** When two people have made changes to copies of the same file, `diff3' can produce a merged output that contains both sets of changes together with warnings about conflicts. One might imagine programs with names like `diff4' and `diff5' to compare more than three files simultaneously, but in practice the need rarely arises. You can use `diff3' to merge three or more sets of changes to a file by merging two change sets at a time. `diff3' can incorporate changes from two modified versions into a common preceding version. This lets you merge the sets of changes represented by the two newer files. Specify the common ancestor version as the second argument and the two newer versions as the first and third arguments, like this: diff3 MINE OLDER YOURS You can remember the order of the arguments by noting that they are in alphabetical order. You can think of this as subtracting OLDER from YOURS and adding the result to MINE, or as merging into MINE the changes that would turn OLDER into YOURS. This merging is well-defined as long as MINE and OLDER match in the neighborhood of each such change. This fails to be true when all three input files differ or when only OLDER differs; we call this a "conflict". When all three input files differ, we call the conflict an "overlap". `diff3' gives you several ways to handle overlaps and conflicts. You can omit overlaps or conflicts, or select only overlaps, or mark conflicts with special `<<<<<<<' and `>>>>>>>' lines. `diff3' can output the merge results as an `ed' script that that can be applied to the first file to yield the merged output. However, it is usually better to have `diff3' generate the merged output directly; this bypasses some problems with `ed'. * Menu: * Which Changes:: Selecting changes to incorporate. * Marking Conflicts:: Marking conflicts. * Bypassing ed:: Generating merged output directly. * Merging Incomplete Lines:: How `diff3' merges incomplete lines. * Saving the Changed File:: Emulating System V behavior. File: diff.info, Node: Which Changes, Next: Marking Conflicts, Up: diff3 Merging Selecting Which Changes to Incorporate ====================================== You can select all unmerged changes from OLDER to YOURS for merging into MINE with the `-e' or `--ed' option. You can select only the nonoverlapping unmerged changes with `-3' or `--easy-only', and you can select only the overlapping changes with `-x' or `--overlap-only'. The `-e', `-3' and `-x' options select only "unmerged changes", i.e. changes where MINE and YOURS differ; they ignore changes from OLDER to YOURS where MINE and YOURS are identical, because they assume that such changes have already been merged. If this assumption is not a safe one, you can use the `-A' or `--show-all' option (*note Marking Conflicts::.). Here is the output of the command `diff3' with each of these three options (*note Sample diff3 Input::., for the complete contents of the files). Notice that `-e' outputs the union of the disjoint sets of changes output by `-3' and `-x'. Output of `diff3 -e lao tzu tao': 11a -- The Way of Lao-Tzu, tr. Wing-tsit Chan . 8c so we may see their result. . Output of `diff3 -3 lao tzu tao': 8c so we may see their result. . Output of `diff3 -x lao tzu tao': 11a -- The Way of Lao-Tzu, tr. Wing-tsit Chan . File: diff.info, Node: Marking Conflicts, Next: Bypassing ed, Prev: Which Changes, Up: diff3 Merging Marking Conflicts ================= `diff3' can mark conflicts in the merged output by bracketing them with special marker lines. A conflict that comes from two files A and B is marked as follows: <<<<<<< A lines from A ======= lines from B >>>>>>> B A conflict that comes from three files A, B and C is marked as follows: <<<<<<< A lines from A ||||||| B lines from B ======= lines from C >>>>>>> C The `-A' or `--show-all' option acts like the `-e' option, except that it brackets conflicts, and it outputs all changes from OLDER to YOURS, not just the unmerged changes. Thus, given the sample input files (*note Sample diff3 Input::.), `diff3 -A lao tzu tao' puts brackets around the conflict where only `tzu' differs: <<<<<<< tzu ======= The Way that can be told of is not the eternal Way; The name that can be named is not the eternal name. >>>>>>> tao And it outputs the three-way conflict as follows: <<<<<<< lao ||||||| tzu They both may be called deep and profound. Deeper and more profound, The door of all subtleties! ======= -- The Way of Lao-Tzu, tr. Wing-tsit Chan >>>>>>> tao The `-E' or `--show-overlap' option outputs less information than the `-A' or `--show-all' option, because it outputs only unmerged changes, and it never outputs the contents of the second file. Thus the `-E' option acts like the `-e' option, except that it brackets the first and third files from three-way overlapping changes. Similarly, `-X' acts like `-x', except it brackets all its (necessarily overlapping) changes. For example, for the three-way overlapping change above, the `-E' and `-X' options output the following: <<<<<<< lao ======= -- The Way of Lao-Tzu, tr. Wing-tsit Chan >>>>>>> tao If you are comparing files that have meaningless or uninformative names, you can use the `-L LABEL' or `--label=LABEL' option to show alternate names in the `<<<<<<<', `|||||||' and `>>>>>>>' brackets. This option can be given up to three times, once for each input file. Thus `diff3 -A -L X -L Y -L Z A B C' acts like `diff3 -A A B C', except that the output looks like it came from files named `X', `Y' and `Z' rather than from files named `A', `B' and `C'. File: diff.info, Node: Bypassing ed, Next: Merging Incomplete Lines, Prev: Marking Conflicts, Up: diff3 Merging Generating the Merged Output Directly ===================================== With the `-m' or `--merge' option, `diff3' outputs the merged file directly. This is more efficient than using `ed' to generate it, and works even with non-text files that `ed' would reject. If you specify `-m' without an `ed' script option, `-A' (`--show-all') is assumed. For example, the command `diff3 -m lao tzu tao' (*note Sample diff3 Input::. for a copy of the input files) would output the following: <<<<<<< tzu ======= The Way that can be told of is not the eternal Way; The name that can be named is not the eternal name. >>>>>>> tao The Nameless is the origin of Heaven and Earth; The Named is the mother of all things. Therefore let there always be non-being, so we may see their subtlety, And let there always be being, so we may see their result. The two are the same, But after they are produced, they have different names. <<<<<<< lao ||||||| tzu They both may be called deep and profound. Deeper and more profound, The door of all subtleties! ======= -- The Way of Lao-Tzu, tr. Wing-tsit Chan >>>>>>> tao File: diff.info, Node: Merging Incomplete Lines, Next: Saving the Changed File, Prev: Bypassing ed, Up: diff3 Merging How `diff3' Merges Incomplete Lines =================================== With `-m', incomplete lines (*note Incomplete Lines::.) are simply copied to the output as they are found; if the merged output ends in an conflict and one of the input files ends in an incomplete line, succeeding `|||||||', `=======' or `>>>>>>>' brackets appear somewhere other than the start of a line because they are appended to the incomplete line. Without `-m', if an `ed' script option is specified and an incomplete line is found, `diff3' generates a warning and acts as if a newline had been present. File: diff.info, Node: Saving the Changed File, Prev: Merging Incomplete Lines, Up: diff3 Merging Saving the Changed File ======================= Traditional Unix `diff3' generates an `ed' script without the trailing `w' and and `q' commands that save the changes. System V `diff3' generates these extra commands. GNU `diff3' normally behaves like traditional Unix `diff3', but with the `-i' option it behaves like System V `diff3' and appends the `w' and `q' commands. The `-i' option requires one of the `ed' script options `-AeExX3', and is incompatible with the merged output option `-m'. File: diff.info, Node: Interactive Merging, Next: Merging with patch, Prev: diff3 Merging, Up: Top Interactive Merging with `sdiff' ******************************** With `sdiff', you can merge two files interactively based on a side-by-side `-y' format comparison (*note Side by Side::.). Use `-o FILE' or `--output=FILE' to specify where to put the merged text. *Note Invoking sdiff::, for more details on the options to `sdiff'. Another way to merge files interactively is to use the Emacs Lisp package `emerge'. *Note emerge: (emacs)emerge, for more information. * Menu: * sdiff Option Summary::Summary of `sdiff' options. * Merge Commands:: Merging two files interactively. File: diff.info, Node: sdiff Option Summary, Next: Merge Commands, Up: Interactive Merging Specifying `diff' Options to `sdiff' ==================================== The following `sdiff' options have the same meaning as for `diff'. *Note diff Options::, for the use of these options. -a -b -d -i -t -v -B -H -I REGEXP --ignore-blank-lines --ignore-case --ignore-matching-lines=REGEXP --ignore-space-change --left-column --minimal --speed-large-files --suppress-common-lines --expand-tabs --text --version --width=COLUMNS For historical reasons, `sdiff' has alternate names for some options. The `-l' option is equivalent to the `--left-column' option, and similarly `-s' is equivalent to `--suppress-common-lines'. The meaning of the `sdiff' `-w' and `-W' options is interchanged from that of `diff': with `sdiff', `-w COLUMNS' is equivalent to `--width=COLUMNS', and `-W' is equivalent to `--ignore-all-space'. `sdiff' without the `-o' option is equivalent to `diff' with the `-y' or `--side-by-side' option (*note Side by Side::.). File: diff.info, Node: Merge Commands, Prev: sdiff Option Summary, Up: Interactive Merging Merge Commands ============== Groups of common lines, with a blank gutter, are copied from the first file to the output. After each group of differing lines, `sdiff' prompts with `%' and pauses, waiting for one of the following commands. Follow each command with RET. Discard both versions. Invoke a text editor on an empty temporary file, then copy the resulting file to the output. Concatenate the two versions, edit the result in a temporary file, then copy the edited result to the output. Edit a copy of the left version, then copy the result to the output. Edit a copy of the right version, then copy the result to the output. Copy the left version to the output. Quit. Copy the right version to the output. Silently copy common lines. Verbosely copy common lines. This is the default. The text editor invoked is specified by the `EDITOR' environment variable if it is set. The default is system-dependent. File: diff.info, Node: Merging with patch, Next: Making Patches, Prev: Interactive Merging, Up: Top Merging with `patch' ******************** `patch' takes comparison output produced by `diff' and applies the differences to a copy of the original file, producing a patched version. With `patch', you can distribute just the changes to a set of files instead of distributing the entire file set; your correspondents can apply `patch' to update their copy of the files with your changes. `patch' automatically determines the diff format, skips any leading or trailing headers, and uses the headers to determine which file to patch. This lets your correspondents feed an article or message containing a difference listing directly to `patch'. `patch' detects and warns about common problems like forward patches. It saves the original version of the files it patches, and saves any patches that it could not apply. It can also maintain a `patchlevel.h' file to ensures that your correspondents apply diffs in the proper order. `patch' accepts a series of diffs in its standard input, usually separated by headers that specify which file to patch. It applies `diff' hunks (*note Hunks::.) one by one. If a hunk does not exactly match the original file, `patch' uses heuristics to try to patch the file as well as it can. If no approximate match can be found, `patch' rejects the hunk and skips to the next hunk. `patch' normally replaces each file F with its new version, saving the original file in `F.orig', and putting reject hunks (if any) into `F.rej'. *Note Invoking patch::, for detailed information on the options to `patch'. *Note Backups::, for more information on how `patch' names backup files. *Note Rejects::, for more information on where `patch' puts reject hunks. * Menu: * patch Input:: Selecting the type of `patch' input. * Imperfect:: Dealing with imperfect patches. * Empty Files:: Removing empty files after patching. * Multiple Patches:: Handling multiple patches in a file specially. * patch Messages:: Messages and questions `patch' can produce. File: diff.info, Node: patch Input, Next: Imperfect, Up: Merging with patch Selecting the `patch' Input Format ================================== `patch' normally determines which `diff' format the patch file uses by examining its contents. For patch files that contain particularly confusing leading text, you might need to use one of the following options to force `patch' to interpret the patch file as a certain format of diff. The output formats listed here are the only ones that `patch' can understand. `--context' context diff. `--ed' `ed' script. `--normal' normal diff. `--unified' unified diff. File: diff.info, Node: Imperfect, Next: Empty Files, Prev: patch Input, Up: Merging with patch Applying Imperfect Patches ========================== `patch' tries to skip any leading text in the patch file, apply the diff, and then skip any trailing text. Thus you can feed a news article or mail message directly to `patch', and it should work. If the entire diff is indented by a constant amount of whitespace, `patch' automatically ignores the indentation. However, certain other types of imperfect input require user intervention. * Menu: * Changed Whitespace:: When tabs and spaces don't match exactly. * Reversed Patches:: Applying reversed patches correctly. * Inexact:: Helping `patch' find close matches. File: diff.info, Node: Changed Whitespace, Next: Reversed Patches, Up: Imperfect Applying Patches with Changed Whitespace ---------------------------------------- Sometimes mailers, editors, or other programs change spaces into tabs, or vice versa. If this happens to a patch file or an input file, the files might look the same, but `patch' will not be able to match them properly. If this problem occurs, use the `-l' or `--ignore-whitespace' option, which makes `patch' compare whitespace loosely so that any sequence of whitespace in the patch file matches any sequence of whitespace in the input files. Non-whitespace characters must still match exactly. Each line of the context must still match a line in the input file. File: diff.info, Node: Reversed Patches, Next: Inexact, Prev: Changed Whitespace, Up: Imperfect Applying Reversed Patches ------------------------- Sometimes people run `diff' with the new file first instead of second. This creates a diff that is "reversed". To apply such patches, give `patch' the `-R' or `--reverse' option. `patch' then attempts to swap each hunk around before applying it. Rejects come out in the swapped format. The `-R' option does not work with `ed' scripts because there is too little information in them to reconstruct the reverse operation. Often `patch' can guess that the patch is reversed. If the first hunk of a patch fails, `patch' reverses the hunk to see if it can apply it that way. If it can, `patch' asks you if you want to have the `-R' option set; if it can't, `patch' continues to apply the patch normally. This method cannot detect a reversed patch if it is a normal diff and the first command is an append (which should have been a delete) since appends always succeed, because a null context matches anywhere. But most patches add or change lines rather than delete them, so most reversed normal diffs begin with a delete, which fails, and `patch' notices. If you apply a patch that you have already applied, `patch' thinks it is a reversed patch and offers to un-apply the patch. This could be construed as a feature. If you did this inadvertently and you don't want to un-apply the patch, just answer `n' to this offer and to the subsequent "apply anyway" question--or type `C-c' to kill the `patch' process. File: diff.info, Node: Inexact, Prev: Reversed Patches, Up: Imperfect Helping `patch' Find Inexact Matches ------------------------------------ For context diffs, and to a lesser extent normal diffs, `patch' can detect when the line numbers mentioned in the patch are incorrect, and it attempts to find the correct place to apply each hunk of the patch. As a first guess, it takes the line number mentioned in the hunk, plus or minus any offset used in applying the previous hunk. If that is not the correct place, `patch' scans both forward and backward 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 it cannot find such a place, and it is reading a context or unified diff, and the maximum fuzz factor is set to 1 or more, then `patch' makes another scan, ignoring the first and last line of context. If that fails, and the maximum fuzz factor is set to 2 or more, it makes another scan, ignoring the first two and last two lines of context are ignored. It continues similarly if the maximum fuzz factor is larger. The `-F LINES' or `--fuzz=LINES' option sets the maximum fuzz factor to LINES. This option only applies to context and unified diffs; it ignores up to LINES lines while looking for the place to install a hunk. Note that a larger fuzz factor increases the odds of making a faulty patch. The default fuzz factor is 2; it may not be set to more than the number of lines of context in the diff, ordinarily 3. If `patch' cannot find a place to install a hunk of the patch, it writes the hunk out to a reject file (*note Rejects::., for information on how reject files are named). It writes out rejected hunks in context format no matter what form the input patch is in. If the input is a normal or `ed' diff, many of the contexts are simply null. The line numbers on the hunks in the reject file may be different from those in the patch file: they show the approximate location where `patch' thinks the failed hunks belong in the new file rather than in the old one. As it completes each hunk, `patch' tells you whether the hunk succeeded or failed, and if it failed, on which line (in the new file) `patch' thinks the hunk should go. If this is different from the line number specified in the diff, it tells you the offset. A single large offset *may* indicate that `patch' installed a hunk in the wrong place. `patch' also tells you if it used a fuzz factor to make the match, in which case you should also be slightly suspicious. `patch' cannot tell if the line numbers are off in an `ed' script, and can only detect wrong line numbers in a normal diff when it finds a change or delete command. It may have the same problem with a context diff using a fuzz factor equal to or greater than the number of lines of context shown in the diff (typically 3). In these cases, you should probably look at a context diff between your original and patched input files to see if the changes make sense. Compiling without errors is a pretty good indication that the patch worked, but not a guarantee. `patch' usually produces the correct results, even when it must make many guesses. However, the results are guaranteed only when the patch is applied to an exact copy of the file that the patch was generated from. File: diff.info, Node: Empty Files, Next: Multiple Patches, Prev: Imperfect, Up: Merging with patch Removing Empty Files ==================== Sometimes when comparing two directories, the first directory contains a file that the second directory does not. If you give `diff' the `-N' or `--new-file' option, it outputs a diff that deletes the contents of this file. By default, `patch' leaves an empty file after applying such a diff. The `-E' or `--remove-empty-files' option to `patch' deletes output files that are empty after applying the diff. File: diff.info, Node: Multiple Patches, Next: patch Messages, Prev: Empty Files, Up: Merging with patch Multiple Patches in a File ========================== If the patch file contains more than one patch, `patch' tries to apply each of them as if they came from separate patch files. This means that it determines the name of the file to patch for each patch, and that it examines the leading text before each patch for file names and prerequisite revision level (*note Making Patches::., for more on that topic). For the second and subsequent patches in the patch file, you can give options and another original file name by separating their argument lists with a `+'. However, the argument list for a second or subsequent patch may not specify a new patch file, since that does not make sense. For example, to tell `patch' to strip the first three slashes from the name of the first patch in the patch file and none from subsequent patches, and to use `code.c' as the first input file, you can use: patch -p3 code.c + -p0 < patchfile The `-S' or `--skip' option ignores the current patch from the patch file, but continue looking for the next patch in the file. Thus, to ignore the first and third patches in the patch file, you can use: patch -S + + -S + < patch file File: diff.info, Node: patch Messages, Prev: Multiple Patches, Up: Merging with patch Messages and Questions from `patch' =================================== `patch' can produce a variety of messages, especially if it has trouble decoding its input. In a few situations where it's not sure how to proceed, `patch' normally prompts you for more information from the keyboard. There are options to suppress printing non-fatal messages and stopping for keyboard input. The message `Hmm...' indicates that `patch' is reading text in the patch file, attempting to determine whether there is a patch in that text, and if so, what kind of patch it is. You can inhibit all terminal output from `patch', unless an error occurs, by using the `-s', `--quiet', or `--silent' option. There are two ways you can prevent `patch' from asking you any questions. The `-f' or `--force' option assumes that you know what you are doing. It assumes the following: * skip patches for which it can't find a file to patch; * patch files even though they have the wrong version for the `Prereq:' line in the patch; * assume that patches are not reversed even if they look like they are. The `-t' or `--batch' option is similar to `-f', in that it suppresses questions, but it makes somewhat different assumptions: * skip patches for which it can't find a file to patch (the same as `-f'); * skip patches for which the file has the wrong version for the `Prereq:' line in the patch; * assume that patches are reversed if they look like they are. `patch' exits with a non-zero status if it creates any reject files. When applying a set of patches in a loop, you should check the exit status, so you don't apply a later patch to a partially patched file. File: diff.info, Node: Making Patches, Next: Invoking cmp, Prev: Merging with patch, Up: Top Tips for Making Patch Distributions *********************************** Here are some things you should keep in mind if you are going to distribute patches for updating a software package. Make sure you have specified the file names correctly, either in a context diff header or with an `Index:' line. If you are patching files in a subdirectory, be sure to tell the patch user to specify a `-p' or `--strip' option as needed. Take care to not send out reversed patches, since these make people wonder whether they have already applied the patch. To save people from partially applying a patch before other patches that should have gone before it, you can make the first patch in the patch file update a file with a name like `patchlevel.h' or `version.c', which contains a patch level or version number. If the input file contains the wrong version number, `patch' will complain immediately. An even clearer way to prevent this problem is to put a `Prereq:' line before the patch. If the leading text in the patch file contains a line that starts with `Prereq:', `patch' takes the next word from that line (normally a version number) and checks whether the next input file contains that word, preceded and followed by either whitespace or a newline. If not, `patch' prompts you for confirmation before proceeding. This makes it difficult to accidentally apply patches in the wrong order. Since `patch' does not handle incomplete lines properly, make sure that all the source files in your program end with a newline whenever you release a version. To create a patch that changes an older version of a package into a newer version, first make a copy of the older version in a scratch directory. Typically you do that by unpacking a `tar' or `shar' archive of the older version. You might be able to reduce the size of the patch by renaming or removing some files before making the patch. If the older version of the package contains any files that the newer version does not, or if any files have been renamed between the two versions, make a list of `rm' and `mv' commands for the user to execute in the old version directory before applying the patch. Then run those commands yourself in the scratch directory. If there are any files that you don't need to include in the patch because they can easily be rebuilt from other files (for example, `TAGS' and output from `yacc' and `makeinfo'), replace the versions in the scratch directory with the newer versions, using `rm' and `ln' or `cp'. Now you can create the patch. The de-facto standard `diff' format for patch distributions is context format with two lines of context, produced by giving `diff' the `-C 2' option. Do not use less than two lines of context, because `patch' typically needs at least two lines for proper operation. Give `diff' the `-P' option in case the newer version of the package contains any files that the older one does not. Make sure to specify the scratch directory first and the newer directory second. Add to the top of the patch a note telling the user any `rm' and `mv' commands to run before applying the patch. Then you can remove the scratch directory. File: diff.info, Node: Invoking cmp, Next: Invoking diff, Prev: Making Patches, Up: Top Invoking `cmp' ************** The `cmp' command compares two files, and if they differ, tells the first byte and line number where they differ. Its arguments are as follows: cmp OPTIONS... FROM-FILE [TO-FILE] The file name `-' is always the standard input. `cmp' also uses the standard input if one file name is omitted. An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble. * Menu: * cmp Options:: Summary of options to `cmp'. File: diff.info, Node: cmp Options, Up: Invoking cmp Options to `cmp' ================ Below is a summary of all of the options that GNU `cmp' accepts. Most options have two equivalent names, one of which is a single letter preceded by `-', and the other of which is a long name preceded by `--'. Multiple single letter options (unless they take an argument) can be combined into a single command line word: `-cl' is equivalent to `-c -l'. Print the differing characters. Display control characters as a `^' followed by a letter of the alphabet and precede characters that have the high bit set with `M-' (which stands for "meta"). Print the (decimal) offsets and (octal) values of all differing bytes. `--print-chars' Print the differing characters. Display control characters as a `^' followed by a letter of the alphabet and precede characters that have the high bit set with `M-' (which stands for "meta"). `--quiet' `--silent' Do not print anything; only return an exit status indicating whether the files differ. `--verbose' Print the (decimal) offsets and (octal) values of all differing bytes. File: diff.info, Node: Invoking diff, Next: Invoking diff3, Prev: Invoking cmp, Up: Top Invoking `diff' *************** The format for running the `diff' command is: diff OPTIONS... FROM-FILE TO-FILE In the simplest case, `diff' compares the contents of the two files FROM-FILE and TO-FILE. A file name of `-' stands for text read from the standard input. As a special case, `diff - -' compares a copy of standard input to itself. If FROM-FILE is a directory and TO-FILE is not, `diff' compares the file in FROM-FILE whose file name is that of TO-FILE, and vice versa. The non-directory file must not be `-'. If both FROM-FILE and TO-FILE are directories, `diff' compares corresponding files in both directories, in alphabetical order; this comparison is not recursive unless the `-r' or `--recursive' option is given. `diff' never compares the actual contents of a directory as if it were a file. The file that is fully specified may not be standard input, because standard input is nameless and the notion of "file with the same name" does not apply. `diff' options begin with `-', so normally FROM-FILE and TO-FILE may not begin with `-'. However, `--' as an argument by itself treats the remaining arguments as file names even if they begin with `-'. An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble. * Menu: * diff Options:: Summary of options to `diff'.