2.2 Custom Functions

Readline provides many functions for manipulating the text of the line, but it isn’t possible to anticipate the needs of all programs. This section describes the various functions and variables defined within the Readline library which allow a user program to add customized functionality to Readline.

Before declaring any functions that customize Readline’s behavior, or using any functionality Readline provides in other code, an application writer should include the file <readline/readline.h> in any file that uses Readline’s features. Since some of the definitions in readline.h use the stdio library, the file <stdio.h> should be included before readline.h.

readline.h defines a C preprocessor variable that should be treated as an integer, RL_READLINE_VERSION, which may be used to conditionally compile application code depending on the installed Readline version. The value is a hexadecimal encoding of the major and minor version numbers of the library, of the form 0xMMmm. MM is the two-digit major version number; mm is the two-digit minor version number. For Readline 4.2, for example, the value of RL_READLINE_VERSION would be 0x0402.