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9.4 The mpedit command

Yet another utility program that is provided is called mpedit, which is used to invoke a text editor on a given source file and optionally jump to a specific line number. It is used as a support command by the mpatrol library when the EDIT or LIST options are used but it can quite easily be used as a command in its own right if properly configured. Because it is a shell script it can be easily configured to support other editors, but this unfortunately limits it to UNIX platforms at the moment.

The first argument to mpedit must be the filename of the source file to be edited or listed. If the source file does not exist then the contents of the MPATROL_SOURCEPATH environment variable will be used to help locate the source file, even if the filename contained an absolute or relative path component. This environment variable should consist of a colon-separated list of directory names which may contain absolute paths or be relative to the current directory; the first directory in the list will be searched first. If the MPATROL_SOURCEPATH environment variable is not set then only the current directory will be searched. You can also use the --source-dir option to add directories to the search path used to locate the source file. Multiple --source-dir options may be given, and each will be prepended to the MPATROL_SOURCEPATH environment variable in the order given on the command line.

If the second argument specifying the line number is omitted then it is assumed to be `1'. The text editor will attempt to jump to the specified line after opening the source file. The text editor that mpedit uses is controlled by setting the EDITOR environment variable. This can be set to the full pathname of the text editor to use or it can be set to the command that would normally be used to invoke the text editor, but it cannot also contain command line options. You can also use the --editor option to specify the text editor on the command line instead of using the value in the EDITOR environment variable.

The currently supported editors are vi, vim, elvis, emacs, xemacs, pico and nano, and if the EDITOR environment variable is not set then the default will be vi. Selecting an unsupported text editor will result in an error. However, you can edit the mpedit file to add support for your own favourite text editor as long as it supports a way to immediately jump to a specific line number when it is first started up. Note that the text editor must also open a new window to edit the source file so that it does not obscure any mpatrol diagnostic messages, and if it does not support this then a new terminal window must be opened for it to use.

If the --listing option is given on the command line then the mpedit command will display a context listing of the source file at the specified line number to the standard error output stream instead of invoking the text editor. The listing will be annotated with line numbers and will also show the contents of the five lines before and after the specified line if possible. Note also that the mpedit command supports the --help and --version options in common with the other mpatrol command line tools.