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GNU Info File | 1993-11-10 | 47KB | 894 lines

This is Info file diff.info, produced by Makeinfo-1.55 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: Top, Up: (dir) 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. This is Edition 1.2, for `diff' 2.4 and `patch' 2.1. * Menu: * Overview:: Preliminary information. * Comparison:: What file comparison means. * Output Formats:: Formats for difference reports. * Comparing Directories:: Comparing files and directories. * Adjusting Output:: Making `diff' output prettier. * diff Performance:: Making `diff' smarter or faster. * Comparing Three Files:: Formats for three-way difference reports. * diff3 Merging:: Merging from a common ancestor. * Interactive Merging:: Interactive merging with `sdiff'. * Merging with patch:: Using `patch' to change old files into new ones. * Making Patches:: Tips for making patch distributions. * Invoking cmp:: How to run `cmp' and a summary of its options. * Invoking diff:: How to run `diff' and a summary of its options. * Invoking diff3:: How to run `diff3' and a summary of its options. * Invoking patch:: How to run `patch' and a summary of its options. * Invoking sdiff:: How to run `sdiff' and a summary of its options. * Incomplete Lines:: Lines that lack trailing newlines. * Projects:: If you think you've found a bug or other shortcoming. * Concept Index:: Index of concepts. File: diff.info, Node: Overview, Next: Comparison, Up: Top Overview ******** Computer users often find occasion to ask how two files differ. Perhaps one file is a newer version of the other file. Or maybe the two files started out as identical copies but were changed by different people. You can use the `diff' command to show differences between two files, or each corresponding file in two directories. `diff' outputs differences between files line by line in any of several formats, selectable by command line options. This set of differences is often called a "diff" or "patch". For files that are identical, `diff' normally produces no output; for binary (non-text) files, `diff' normally reports only that they are different. You can use the `cmp' command to show the offsets and line numbers where two files differ. `cmp' can also show all the characters that differ between the two files, side by side. Another way to compare two files character by character is the Emacs command `M-x compare-windows'. *Note Other Window: (emacs)Other Window, for more information on that command. You can use the `diff3' command to show differences among three files. When two people have made independent changes to a common original, `diff3' can report the differences between the original and the two changed versions, and can produce a merged file that contains both persons' changes together with warnings about conflicts. You can use the `sdiff' command to merge two files interactively. You can use the set of differences produced by `diff' to distribute updates to text files (such as program source code) to other people. This method is especially useful when the differences are small compared to the complete files. Given `diff' output, you can use the `patch' program to update, or "patch", a copy of the file. If you think of `diff' as subtracting one file from another to produce their difference, you can think of `patch' as adding the difference to one file to reproduce the other. This manual first concentrates on making diffs, and later shows how to use diffs to update files. GNU `diff' was written by Mike Haertel, David Hayes, Richard Stallman, Len Tower, and Paul Eggert. Wayne Davison designed and implemented the unified output format. The basic algorithm is described in "An O(ND) Difference Algorithm and its Variations", Eugene W. Myers, `Algorithmica' Vol. 1 No. 2, 1986, pp. 251-266; and in "A File Comparison Program", Webb Miller and Eugene W. Myers, `Software--Practice and Experience' Vol. 15 No. 11, 1985, pp. 1025-1040. The algorithm was independently discovered as described in "Algorithms for Approximate String Matching", E. Ukkonen, `Information and Control' Vol. 64, 1985, pp. 100-118. GNU `diff3' was written by Randy Smith. GNU `sdiff' was written by Thomas Lord. GNU `cmp' was written by Torbjorn Granlund and David MacKenzie. `patch' was written mainly by Larry Wall; the GNU enhancements were written mainly by Wayne Davison and David MacKenzie. Parts of this manual are adapted from a manual page written by Larry Wall, with his permission. File: diff.info, Node: Comparison, Next: Output Formats, Prev: Overview, Up: Top What Comparison Means ********************* There are several ways to think about the differences between two files. One way to think of the differences is as a series of lines that were deleted from, inserted in, or changed in one file to produce the other file. `diff' compares two files line by line, finds groups of lines that differ, and reports each group of differing lines. It can report the differing lines in several formats, which have different purposes. GNU `diff' can show whether files are different without detailing the differences. It also provides ways to suppress certain kinds of differences that are not important to you. Most commonly, such differences are changes in the amount of white space between words or lines. `diff' also provides ways to suppress differences in alphabetic case or in lines that match a regular expression that you provide. These options can accumulate; for example, you can ignore changes in both white space and alphabetic case. Another way to think of the differences between two files is as a sequence of pairs of characters that can be either identical or different. `cmp' reports the differences between two files character by character, instead of line by line. As a result, it is more useful than `diff' for comparing binary files. For text files, `cmp' is useful mainly when you want to know only whether two files are identical. To illustrate the effect that considering changes character by character can have compared with considering them line by line, think of what happens if a single newline character is added to the beginning of a file. If that file is then compared with an otherwise identical file that lacks the newline at the beginning, `diff' will report that a blank line has been added to the file, while `cmp' will report that almost every character of the two files differs. `diff3' normally compares three input files line by line, finds groups of lines that differ, and reports each group of differing lines. Its output is designed to make it easy to inspect two different sets of changes to the same file. * Menu: * Hunks:: Groups of differing lines. * White Space:: Suppressing differences in white space. * Blank Lines:: Suppressing differences in blank lines. * Case Folding:: Suppressing differences in alphabetic case. * Specified Folding:: Suppressing differences that match regular expressions. * Brief:: Summarizing which files are different. * Binary:: Comparing binary files or forcing text comparisons. File: diff.info, Node: Hunks, Next: White Space, Up: Comparison Hunks ===== When comparing two files, `diff' finds sequences of lines common to both files, interspersed with groups of differing lines called "hunks". Comparing two identical files yields one sequence of common lines and no hunks, because no lines differ. Comparing two entirely different files yields no common lines and one large hunk that contains all lines of both files. In general, there are many ways to match up lines between two given files. `diff' tries to minimize the total hunk size by finding large sequences of common lines interspersed with small hunks of differing lines. For example, suppose the file `F' contains the three lines `a', `b', `c', and the file `G' contains the same three lines in reverse order `c', `b', `a'. If `diff' finds the line `c' as common, then the command `diff F G' produces this output: 1,2d0 < a < b 3a2,3 > b > a But if `diff' notices the common line `b' instead, it produces this output: 1c1 < a --- > c 3c3 < c --- > a It is also possible to find `a' as the common line. `diff' does not always find an optimal matching between the files; it takes shortcuts to run faster. But its output is usually close to the shortest possible. You can adjust this tradeoff with the `--minimal' option (*note diff Performance::.). File: diff.info, Node: White Space, Next: Blank Lines, Prev: Hunks, Up: Comparison Suppressing Differences in Blank and Tab Spacing ================================================ The `-b' and `--ignore-space-change' options ignore white space at line end, and considers all other sequences of one or more white space characters to be equivalent. With these options, `diff' considers the following two lines to be equivalent, where `$' denotes the line end: Here lyeth muche rychnesse in lytell space. -- John Heywood$ Here lyeth muche rychnesse in lytell space. -- John Heywood $ The `-w' and `--ignore-all-space' options are stronger than `-b'. They ignore difference even if one file has white space where the other file has none. "White space" characters include tab, vertical tab, form feed, carriage return, and space; some locales may define additional characters to be white space. With these options, `diff' considers the following two lines to be equivalent, where `$' denotes the line end and `^M' denotes a carriage return: Here lyeth muche rychnesse in lytell space.-- John Heywood$ He relyeth much erychnes seinly tells pace. --John Heywood ^M$ File: diff.info, Node: Blank Lines, Next: Case Folding, Prev: White Space, Up: Comparison Suppressing Differences in Blank Lines ====================================== The `-B' and `--ignore-blank-lines' options ignore insertions or deletions of blank lines. These options normally affect only lines that are completely empty; they do not affect lines that look empty but contain space or tab characters. With these options, for example, a file containing 1. A point is that which has no part. 2. A line is breadthless length. -- Euclid, The Elements, I is considered identical to a file containing 1. A point is that which has no part. 2. A line is breadthless length. -- Euclid, The Elements, I File: diff.info, Node: Case Folding, Next: Specified Folding, Prev: Blank Lines, Up: Comparison Suppressing Case Differences ============================ GNU `diff' can treat lowercase letters as equivalent to their uppercase counterparts, so that, for example, it considers `Funky Stuff', `funky STUFF', and `fUNKy stuFf' to all be the same. To request this, use the `-i' or `--ignore-case' option. File: diff.info, Node: Specified Folding, Next: Brief, Prev: Case Folding, Up: Comparison Suppressing Lines Matching a Regular Expression =============================================== To ignore insertions and deletions of lines that match a regular expression, use the `-I REGEXP' or `--ignore-matching-lines=REGEXP' option. You should escape regular expressions that contain shell metacharacters to prevent the shell from expanding them. For example, `diff -I '^[0-9]'' ignores all changes to lines beginning with a digit. However, `-I' only ignores the insertion or deletion of lines that contain the regular expression if every changed line in the hunk--every insertion and every deletion--matches the regular expression. In other words, for each nonignorable change, `diff' prints the complete set of changes in its vicinity, including the ignorable ones. You can specify more than one regular expression for lines to ignore by using more than one `-I' option. `diff' tries to match each line against each regular expression, starting with the last one given. File: diff.info, Node: Brief, Next: Binary, Prev: Specified Folding, Up: Comparison Summarizing Which Files Differ ============================== When you only want to find out whether files are different, and you don't care what the differences are, you can use the summary output format. In this format, instead of showing the differences between the files, `diff' simply reports whether files differ. The `-q' and `--brief' options select this output format. This format is especially useful when comparing the contents of two directories. It is also much faster than doing the normal line by line comparisons, because `diff' can stop analyzing the files as soon as it knows that there are any differences. You can also get a brief indication of whether two files differ by using `cmp'. For files that are identical, `cmp' produces no output. When the files differ, by default, `cmp' outputs the byte offset and line number where the first difference occurs. You can use the `-s' option to suppress that information, so that `cmp' produces no output and reports whether the files differ using only its exit status (*note Invoking cmp::.). Unlike `diff', `cmp' cannot compare directories; it can only compare two files. File: diff.info, Node: Binary, Prev: Brief, Up: Comparison Binary Files and Forcing Text Comparisons ========================================= If `diff' thinks that either of the two files it is comparing is binary (a non-text file), it normally treats that pair of files much as if the summary output format had been selected (*note Brief::.), and reports only that the binary files are different. This is because line by line comparisons are usually not meaningful for binary files. `diff' determines whether a file is text or binary by checking the first few bytes in the file; the exact number of bytes is system dependent, but it is typically several thousand. If every character in that part of the file is non-null, `diff' considers the file to be text; otherwise it considers the file to be binary. Sometimes you might want to force `diff' to consider files to be text. For example, you might be comparing text files that contain null characters; `diff' would erroneously decide that those are non-text files. Or you might be comparing documents that are in a format used by a word processing system that uses null characters to indicate special formatting. You can force `diff' to consider all files to be text files, and compare them line by line, by using the `-a' or `--text' option. If the files you compare using this option do not in fact contain text, they will probably contain few newline characters, and the `diff' output will consist of hunks showing differences between long lines of whatever characters the files contain. You can also force `diff' to consider all files to be binary files, and report only whether they differ (but not how). Use the `--brief' option for this. If you want to compare two files byte by byte, you can use the `cmp' program with the `-l' option to show the values of each differing byte in the two files. With GNU `cmp', you can also use the `-c' option to show the ASCII representation of those bytes. *Note Invoking cmp::, for more information. If `diff3' thinks that any of the files it is comparing is binary (a non-text file), it normally reports an error, because such comparisons are usually not useful. `diff3' uses the same test as `diff' to decide whether a file is binary. As with `diff', if the input files contain a few non-text characters but otherwise are like text files, you can force `diff3' to consider all files to be text files and compare them line by line by using the `-a' or `--text' options. File: diff.info, Node: Output Formats, Next: Comparing Directories, Prev: Comparison, Up: Top `diff' Output Formats ********************* `diff' has several mutually exclusive options for output format. The following sections describe each format, illustrating how `diff' reports the differences between two sample input files. * Menu: * Sample diff Input:: Sample `diff' input files for examples. * Normal:: Showing differences without surrounding text. * Context:: Showing differences with the surrounding text. * Side by Side:: Showing differences in two columns. * Scripts:: Generating scripts for other programs. * If-then-else:: Merging files with if-then-else. File: diff.info, Node: Sample diff Input, Next: Normal, Up: Output Formats Two Sample Input Files ====================== Here are two sample files that we will use in numerous examples to illustrate the output of `diff' and how various options can change it. This is the file `lao': 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 outcome. The two are the same, But after they are produced, they have different names. This is the file `tzu': 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 outcome. The two are the same, But after they are produced, they have different names. They both may be called deep and profound. Deeper and more profound, The door of all subtleties! In this example, the first hunk contains just the first two lines of `lao', the second hunk contains the fourth line of `lao' opposing the second and third lines of `tzu', and the last hunk contains just the last three lines of `tzu'. File: diff.info, Node: Normal, Next: Context, Prev: Sample diff Input, Up: Output Formats Showing Differences Without Context =================================== The "normal" `diff' output format shows each hunk of differences without any surrounding context. Sometimes such output is the clearest way to see how lines have changed, without the clutter of nearby unchanged lines (although you can get similar results with the context or unified formats by using 0 lines of context). However, this format is no longer widely used for sending out patches; for that purpose, the context format (*note Context Format::.) and the unified format (*note Unified Format::.) are superior. Normal format is the default for compatibility with older versions of `diff' and the Posix standard. * Menu: * Detailed Normal:: A detailed description of normal output format. * Example Normal:: Sample output in the normal format. File: diff.info, Node: Detailed Normal, Next: Example Normal, Up: Normal Detailed Description of Normal Format ------------------------------------- The normal output format consists of one or more hunks of differences; each hunk shows one area where the files differ. Normal format hunks look like this: CHANGE-COMMAND < FROM-FILE-LINE < FROM-FILE-LINE... --- > TO-FILE-LINE > TO-FILE-LINE... There are three types of change commands. Each consists of a line number or comma-separated range of lines in the first file, a single character indicating the kind of change to make, and a line number or comma-separated range of lines in the second file. All line numbers are the original line numbers in each file. The types of change commands `LaR' Add the lines in range R of the second file after line L of the first file. For example, `8a12,15' means append lines 12-15 of file 2 after line 8 of file 1; or, if changing file 2 into file 1, delete lines 12-15 of file 2. `FcT' Replace the lines in range F of the first file with lines in range T of the second file. This is like a combined add and delete, but more compact. For example, `5,7c8,10' means change lines 5-7 of file 1 to read as lines 8-10 of file 2; or, if changing file 2 into file 1, change lines 8-10 of file 2 to read as lines 5-7 of file 1. `RdL' Delete the lines in range R from the first file; line L is where they would have appeared in the second file had they not been deleted. For example, `5,7d3' means delete lines 5-7 of file 1; or, if changing file 2 into file 1, append lines 5-7 of file 1 after line 3 of file 2. File: diff.info, Node: Example Normal, Prev: Detailed Normal, Up: Normal An Example of Normal Format --------------------------- Here is the output of the command `diff lao tzu' (*note Sample diff Input::., for the complete contents of the two files). Notice that it shows only the lines that are different between the two files. 1,2d0 < The Way that can be told of is not the eternal Way; < The name that can be named is not the eternal name. 4c2,3 < The Named is the mother of all things. --- > The named is the mother of all things. > 11a11,13 > They both may be called deep and profound. > Deeper and more profound, > The door of all subtleties! File: diff.info, Node: Context, Next: Side by Side, Prev: Normal, Up: Output Formats Showing Differences in Their Context ==================================== Usually, when you are looking at the differences between files, you will also want to see the parts of the files near the lines that differ, to help you understand exactly what has changed. These nearby parts of the files are called the "context". GNU `diff' provides two output formats that show context around the differing lines: "context format" and "unified format". It can optionally show in which function or section of the file the differing lines are found. If you are distributing new versions of files to other people in the form of `diff' output, you should use one of the output formats that show context so that they can apply the diffs even if they have made small changes of their own to the files. `patch' can apply the diffs in this case by searching in the files for the lines of context around the differing lines; if those lines are actually a few lines away from where the diff says they are, `patch' can adjust the line numbers accordingly and still apply the diff correctly. *Note Imperfect::, for more information on using `patch' to apply imperfect diffs. * Menu: * Context Format:: An output format that shows surrounding lines. * Unified Format:: A more compact output format that shows context. * Sections:: Showing which sections of the files differences are in. * Alternate Names:: Showing alternate file names in context headers. File: diff.info, Node: Context Format, Next: Unified Format, Up: Context Context Format -------------- The context output format shows several lines of context around the lines that differ. It is the standard format for distributing updates to source code. To select this output format, use the `-C LINES', `--context[=LINES]', or `-c' option. The argument LINES that some of these options take is the number of lines of context to show. If you do not specify LINES, it defaults to three. For proper operation, `patch' typically needs at least two lines of context. * Menu: * Detailed Context:: A detailed description of the context output format. * Example Context:: Sample output in context format. * Less Context:: Another sample with less context. File: diff.info, Node: Detailed Context, Next: Example Context, Up: Context Format Detailed Description of Context Format ...................................... The context output format starts with a two-line header, which looks like this: *** FROM-FILE FROM-FILE-MODIFICATION-TIME --- TO-FILE TO-FILE-MODIFICATION TIME You can change the header's content with the `-L LABEL' or `--label=LABEL' option; see *Note Alternate Names::. Next come one or more hunks of differences; each hunk shows one area where the files differ. Context format hunks look like this: *************** *** FROM-FILE-LINE-RANGE **** FROM-FILE-LINE FROM-FILE-LINE... --- TO-FILE-LINE-RANGE ---- TO-FILE-LINE TO-FILE-LINE... The lines of context around the lines that differ start with two space characters. The lines that differ between the two files start with one of the following indicator characters, followed by a space character: A line that is part of a group of one or more lines that changed between the two files. There is a corresponding group of lines marked with `!' in the part of this hunk for the other file. An "inserted" line in the second file that corresponds to nothing in the first file. A "deleted" line in the first file that corresponds to nothing in the second file. If all of the changes in a hunk are insertions, the lines of FROM-FILE are omitted. If all of the changes are deletions, the lines of TO-FILE are omitted. File: diff.info, Node: Example Context, Next: Less Context, Prev: Detailed Context, Up: Context Format An Example of Context Format ............................ Here is the output of `diff -c lao tzu' (*note Sample diff Input::., for the complete contents of the two files). Notice that up to three lines that are not different are shown around each line that is different; they are the context lines. Also notice that the first two hunks have run together, because their contents overlap. *** lao Sat Jan 26 23:30:39 1991 --- tzu Sat Jan 26 23:30:50 1991 *************** *** 1,7 **** - 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, --- 1,6 ---- 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, *************** *** 9,11 **** --- 8,13 ---- The two are the same, But after they are produced, they have different names. + They both may be called deep and profound. + Deeper and more profound, + The door of all subtleties! File: diff.info, Node: Less Context, Prev: Example Context, Up: Context Format An Example of Context Format with Less Context .............................................. Here is the output of `diff --context=1 lao tzu' (*note Sample diff Input::., for the complete contents of the two files). Notice that at most one context line is reported here. *** lao Sat Jan 26 23:30:39 1991 --- tzu Sat Jan 26 23:30:50 1991 *************** *** 1,5 **** - 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, --- 1,4 ---- The Nameless is the origin of Heaven and Earth; ! The named is the mother of all things. ! Therefore let there always be non-being, *************** *** 11 **** --- 10,13 ---- they have different names. + They both may be called deep and profound. + Deeper and more profound, + The door of all subtleties! File: diff.info, Node: Unified Format, Next: Sections, Prev: Context Format, Up: Context Unified Format -------------- The unified output format is a variation on the context format that is more compact because it omits redundant context lines. To select this output format, use the `-U LINES', `--unified[=LINES]', or `-u' option. The argument LINES is the number of lines of context to show. When it is not given, it defaults to three. At present, only GNU `diff' can produce this format and only GNU `patch' can automatically apply diffs in this format. For proper operation, `patch' typically needs at least two lines of context. * Menu: * Detailed Unified:: A detailed description of unified format. * Example Unified:: Sample output in unified format. File: diff.info, Node: Detailed Unified, Next: Example Unified, Up: Unified Format Detailed Description of Unified Format ...................................... The unified output format starts with a two-line header, which looks like this: --- FROM-FILE FROM-FILE-MODIFICATION-TIME +++ TO-FILE TO-FILE-MODIFICATION-TIME You can change the header's content with the `-L LABEL' or `--label=LABEL' option; see *Note Alternate Names::. Next come one or more hunks of differences; each hunk shows one area where the files differ. Unified format hunks look like this: @@ FROM-FILE-RANGE TO-FILE-RANGE @@ LINE-FROM-EITHER-FILE LINE-FROM-EITHER-FILE... The lines common to both files begin with a space character. The lines that actually differ between the two files have one of the following indicator characters in the left column: A line was added here to the first file. A line was removed here from the first file. File: diff.info, Node: Example Unified, Prev: Detailed Unified, Up: Unified Format An Example of Unified Format ............................ Here is the output of the command `diff -u lao tzu' (*note Sample diff Input::., for the complete contents of the two files): --- lao Sat Jan 26 23:30:39 1991 +++ tzu Sat Jan 26 23:30:50 1991 @@ -1,7 +1,6 @@ -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. +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, @@ -9,3 +8,6 @@ The two are the same, But after they are produced, they have different names. +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! File: diff.info, Node: Sections, Next: Alternate Names, Prev: Unified Format, Up: Context Showing Which Sections Differences Are in ----------------------------------------- Sometimes you might want to know which part of the files each change falls in. If the files are source code, this could mean which function was changed. If the files are documents, it could mean which chapter or appendix was changed. GNU `diff' can show this by displaying the nearest section heading line that precedes the differing lines. Which lines are "section headings" is determined by a regular expression. * Menu: * Specified Headings:: Showing headings that match regular expressions. * C Function Headings:: Showing headings of C functions. File: diff.info, Node: Specified Headings, Next: C Function Headings, Up: Sections Showing Lines That Match Regular Expressions ............................................ To show in which sections differences occur for files that are not source code for C or similar languages, use the `-F REGEXP' or `--show-function-line=REGEXP' option. `diff' considers lines that match the argument REGEXP to be the beginning of a section of the file. Here are suggested regular expressions for some common languages: `^[A-Za-z_]' C, C++, Prolog Lisp `^@$chapter\|appendix\|unnumbered\|chapheading$' Texinfo This option does not automatically select an output format; in order to use it, you must select the context format (*note Context Format::.) or unified format (*note Unified Format::.). In other output formats it has no effect. The `-F' and `--show-function-line' options find the nearest unchanged line that precedes each hunk of differences and matches the given regular expression. Then they add that line to the end of the line of asterisks in the context format, or to the `@@' line in unified format. If no matching line exists, they leave the output for that hunk unchanged. If that line is more than 40 characters long, they output only the first 40 characters. You can specify more than one regular expression for such lines; `diff' tries to match each line against each regular expression, starting with the last one given. This means that you can use `-p' and `-F' together, if you wish. File: diff.info, Node: C Function Headings, Prev: Specified Headings, Up: Sections Showing C Function Headings ........................... To show in which functions differences occur for C and similar languages, you can use the `-p' or `--show-c-function' option. This option automatically selects the context output format (*note Context Format::.), with the default number of lines of context. You can override that number with `-C LINES' later in the command line. You can override both the format and the number with `-U LINES' later in the command line. The `-p' and `--show-c-function' options are equivalent to `-c -F'^[_a-zA-Z$]'' (*note Specified Headings::.). GNU `diff' provides them for the sake of convenience. File: diff.info, Node: Alternate Names, Prev: Sections, Up: Context Showing Alternate File Names ---------------------------- If you are comparing two files that have meaningless or uninformative names, you might want `diff' to show alternate names in the header of the context and unified output formats. To do this, use the `-L LABEL' or `--label=LABEL' option. The first time you give this option, its argument replaces the name and date of the first file in the header; the second time, its argument replaces the name and date of the second file. If you give this option more than twice, `diff' reports an error. The `-L' option does not affect the file names in the `pr' header when the `-l' or `--paginate' option is used (*note Pagination::.). Here are the first two lines of the output from `diff -C2 -Loriginal -Lmodified lao tzu': *** original --- modified File: diff.info, Node: Side by Side, Next: Scripts, Prev: Context, Up: Output Formats Showing Differences Side by Side ================================ `diff' can produce a side by side difference listing of two files. The files are listed in two columns with a gutter between them. The gutter contains one of the following markers: white space The corresponding lines are in common. That is, either the lines are identical, or the difference is ignored because of one of the `--ignore' options (*note White Space::.). The corresponding lines differ, and they are either both complete or both incomplete. The files differ and only the first file contains the line. The files differ and only the second file contains the line. Only the first file contains the line, but the difference is ignored. Only the second file contains the line, but the difference is ignored. The corresponding lines differ, and only the first line is incomplete. The corresponding lines differ, and only the second line is incomplete. Normally, an output line is incomplete if and only if the lines that it contains are incomplete; *Note Incomplete Lines::. However, when an output line represents two differing lines, one might be incomplete while the other is not. In this case, the output line is complete, but its the gutter is marked `\' if the first line is incomplete, `/' if the second line is. Side by side format is sometimes easiest to read, but it has limitations. It generates much wider output than usual, and truncates lines that are too long to fit. Also, it relies on lining up output more heavily than usual, so its output looks particularly bad if you use varying width fonts, nonstandard tab stops, or nonprinting characters. You can use the `sdiff' command to interactively merge side by side differences. *Note Interactive Merging::, for more information on merging files. * Menu: * Side by Side Format:: Controlling side by side output format. * Example Side by Side:: Sample side by side output. File: diff.info, Node: Side by Side Format, Next: Example Side by Side, Up: Side by Side Controlling Side by Side Format =============================== The `-y' or `--side-by-side' option selects side by side format. Because side by side output lines contain two input lines, they are wider than usual. They are normally 130 columns, which can fit onto a traditional printer line. You can set the length of output lines with the `-W COLUMNS' or `--width=COLUMNS' option. The output line is split into two halves of equal length, separated by a small gutter to mark differences; the right half is aligned to a tab stop so that tabs line up. Input lines that are too long to fit in half of an output line are truncated for output. The `--left-column' option prints only the left column of two common lines. The `--suppress-common-lines' option suppresses common lines entirely. File: diff.info, Node: Example Side by Side, Prev: Side by Side Format, Up: Side by Side An Example of Side by Side Format --------------------------------- Here is the output of the command `diff -y -W 72 lao tzu' (*note Sample diff Input::., for the complete contents of the two files). The Way that can be told of is n < The name that can be named is no < The Nameless is the origin of He The Nameless is the origin of He The Named is the mother of all t | The named is the mother of all t > Therefore let there always be no Therefore let there always be no so we may see their subtlety, so we may see their subtlety, And let there always be being, And let there always be being, so we may see their outcome. so we may see their outcome. The two are the same, The two are the same, But after they are produced, But after they are produced, they have different names. they have different names. > They both may be called deep and > Deeper and more profound, > The door of all subtleties! File: diff.info, Node: Scripts, Next: If-then-else, Prev: Side by Side, Up: Output Formats Making Edit Scripts =================== Several output modes produce command scripts for editing FROM-FILE to produce TO-FILE. * Menu: * ed Scripts:: Using `diff' to produce commands for `ed'. * Forward ed:: Making forward `ed' scripts. * RCS:: A special `diff' output format used by RCS. File: diff.info, Node: ed Scripts, Next: Forward ed, Up: Scripts `ed' Scripts ------------ `diff' can produce commands that direct the `ed' text editor to change the first file into the second file. Long ago, this was the only output mode that was suitable for editing one file into another automatically; today, with `patch', it is almost obsolete. Use the `-e' or `--ed' option to select this output format. Like the normal format (*note Normal::.), this output format does not show any context; unlike the normal format, it does not include the information necessary to apply the diff in reverse (to produce the first file if all you have is the second file and the diff). If the file `d' contains the output of `diff -e old new', then the command `(cat d && echo w) | ed - old' edits `old' to make it a copy of `new'. More generally, if `d1', `d2', ..., `dN' contain the outputs of `diff -e old new1', `diff -e new1 new2', ..., `diff -e newN-1 newN', respectively, then the command `(cat d1 d2 ... dN && echo w) | ed - old' edits `old' to make it a copy of `newN'. * Menu: * Detailed ed:: A detailed description of `ed' format. * Example ed:: A sample `ed' script. File: diff.info, Node: Detailed ed, Next: Example ed, Up: ed Scripts Detailed Description of `ed' Format ................................... The `ed' output format consists of one or more hunks of differences. The changes closest to the ends of the files come first so that commands that change the number of lines do not affect how `ed' interprets line numbers in succeeding commands. `ed' format hunks look like this: CHANGE-COMMAND TO-FILE-LINE TO-FILE-LINE... . Because `ed' uses a single period on a line to indicate the end of input, GNU `diff' protects lines of changes that contain a single period on a line by writing two periods instead, then writing a subsequent `ed' command to change the two periods into one. The `ed' format cannot represent an incomplete line, so if the second file ends in a changed incomplete line, `diff' reports an error and then pretends that a newline was appended. There are three types of change commands. Each consists of a line number or comma-separated range of lines in the first file and a single character indicating the kind of change to make. All line numbers are the original line numbers in the file. The types of change commands Add text from the second file after line L in the first file. For example, `8a' means to add the following lines after line 8 of file 1. Replace the lines in range R in the first file with the following lines. Like a combined add and delete, but more compact. For example, `5,7c' means change lines 5-7 of file 1 to read as the text file 2. Delete the lines in range R from the first file. For example, `5,7d' means delete lines 5-7 of file 1. File: diff.info, Node: Example ed, Prev: Detailed ed, Up: ed Scripts Example `ed' Script ................... Here is the output of `diff -e lao tzu' (*note Sample diff Input::., for the complete contents of the two files): 11a They both may be called deep and profound. Deeper and more profound, The door of all subtleties! . 4c The named is the mother of all things. . 1,2d File: diff.info, Node: Forward ed, Next: RCS, Prev: ed Scripts, Up: Scripts Forward `ed' Scripts -------------------- `diff' can produce output that is like an `ed' script, but with hunks in forward (front to back) order. The format of the commands is also changed slightly: command characters precede the lines they modify, spaces separate line numbers in ranges, and no attempt is made to disambiguate hunk lines consisting of a single period. Like `ed' format, forward `ed' format cannot represent incomplete lines. Forward `ed' format is not very useful, because neither `ed' nor `patch' can apply diffs in this format. It exists mainly for compatibility with older versions of `diff'. Use the `-f' or `--forward-ed' option to select it. File: diff.info, Node: RCS, Prev: Forward ed, Up: Scripts RCS Scripts ----------- The RCS output format is designed specifically for use by the Revision Control System, which is a set of free programs used for organizing different versions and systems of files. Use the `-n' or `--rcs' option to select this output format. It is like the forward `ed' format (*note Forward ed::.), but it can represent arbitrary changes to the contents of a file because it avoids the forward `ed' format's problems with lines consisting of a single period and with incomplete lines. Instead of ending text sections with a line consisting of a single period, each command specifies the number of lines it affects; a combination of the `a' and `d' commands are used instead of `c'. Also, if the second file ends in a changed incomplete line, then the output also ends in an incomplete line. Here is the output of `diff -n lao tzu' (*note Sample diff Input::., for the complete contents of the two files): d1 2 d4 1 a4 2 The named is the mother of all things. a11 3 They both may be called deep and profound. Deeper and more profound, The door of all subtleties! File: diff.info, Node: If-then-else, Prev: Scripts, Up: Output Formats Merging Files with If-then-else =============================== You can use `diff' to merge two files of C source code. The output of `diff' in this format contains all the lines of both files. Lines common to both files are output just once; the differing parts are separated by the C preprocessor directives `#ifdef NAME' or `#ifndef NAME', `#else', and `#endif'. When compiling the output, you select which version to use by either defining or leaving undefined the macro NAME. To merge two files, use `diff' with the `-D NAME' or `--ifdef=NAME' option. The argument NAME is the C preprocessor identifier to use in the `#ifdef' and `#ifndef' directives. For example, if you change an instance of `wait (&s)' to `waitpid (-1, &s, 0)' and then merge the old and new files with the `--ifdef=HAVE_WAITPID' option, then the affected part of your code might look like this: do { #ifndef HAVE_WAITPID if ((w = wait (&s)) < 0 && errno != EINTR) #else /* HAVE_WAITPID */ if ((w = waitpid (-1, &s, 0)) < 0 && errno != EINTR) #endif /* HAVE_WAITPID */ return w; } while (w != child); You can specify formats for languages other than C by using line group formats and line formats, as described in the next sections. * Menu: * Line Group Formats:: Formats for general if-then-else line groups. * Line Formats:: Formats for each line in a line group. * Detailed If-then-else:: A detailed description of if-then-else format. * Example If-then-else:: Sample if-then-else format output.