Richard Stallman

Debugging with GDB: The GNU Source-Level Debugger, Tenth Edition, for GDB version 8.1.50.20180116-git. This book is available for free at gnu.org. This book is printed in grayscale.The purpose of a debugger such as gdb is to allow you to see what is going on "inside" another program while it executes - or what another program was doing at the moment it crashed. gdb can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: - Start your program, specifying anything that might affect its behavior. - Make your program stop on specified conditions. - Examine what has happened, when your program has stopped. - Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere "extension language"; it is a full computer programming language in its own right. You can use it as you would any other programming language. Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables. This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information. Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing. This is the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 24.5. As Emacs Lisp became such a big project over the years, we had to split this reference manual in two parts that are two separate physical books. To keep it consistent with our digital manual, the references and page numbers cover both physical books as it were one. Therefore please note that you probably want to have both parts.

Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere "extension language"; it is a full computer programming language in its own right. You can use it as you would any other programming language. Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables. This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information. Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing. This is the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 24.5. As Emacs Lisp became such a big project over the years, we had to split this reference manual in two parts that are two separate physical books. To keep it consistent with our digital manual, the references and page numbers cover both physical books as it were one. Therefore please note that you probably want to have both parts.

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 byte and line numbers where two files differ. cmp can also show all the bytes that differ between the two files, side by side. A way to compare two files character by character is the Emacs command M-x compare-windows. See Section "Other Window" in The GNU Emacs Manual, 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.

This manual attempts to be a full description of Emacs Lisp. This manual presumes considerable familiarity with the use of Emacs for editing. Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere extension language; it is a full computer programming language in its own right. You can use it as you would any other programming language. Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specically to editing. This is edition 3.1 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 25.2. This manual is available online for free at gnu.org. This manual is printed in grayscale.

Biographie ber Richard Stallman, den Verfasser der GNU GPL, Autor des gcc und Gr nder der Free Software Foundation.