Emacs Part of Elisp

1. Buffer related
2. File System Related
- 2.1. Traversing
- 2.2. Predicates
3. Other
- 3.1. make-obsolete-variable

1 Buffer related

with-temp-buffer (with-temp-buffer &rest BODY) Create a temporary buffer, and evaluate BODY there like progn.
(insert-file-contents FILENAME &optional VISIT BEG END REPLACE): Insert contents of file FILENAME after point.
(secure-hash ALGORITHM OBJECT &optional START END BINARY): the object can be a buffer. This can be used to compare if a file has changed.
(current-buffer): Return the current buffer as a Lisp object.
(message FORMAT-STRING &rest ARGS): Display a message at the bottom of the screen.

2 File System Related

2.1 Traversing

(directory-files DIRECTORY &optional FULL MATCH NOSORT)

Return a list of names of files in DIRECTORY.

Usage example:

(bib-files (directory-files bib-dir t ".*\.bib$"))

2.2 Predicates

directory-files will throw error if the directory does not exist. So a safe way is to check if the directory exists first. This predicate does this:

(file-exists-p FILENAME)

Directory is also a file.

Other predicates includes:

file-readable-p
file-executable-p
file-writable-p
file-accessible-directory-p

3 Other

(defalias SYMBOL DEFINITION &optional DOCSTRING): Set SYMBOL's function definition to DEFINITION. E.g. (defalias 'helm-bibtex-get-value 'bibtex-completion-get-value), serves as a temporary patch for helm-bibtex update its API to bibtex-completion

3.1 make-obsolete-variable

(make-obsolete-variable OBSOLETE-NAME CURRENT-NAME WHEN &optional ACCESS-TYPE)

Make the byte-compiler warn that OBSOLETE-NAME is obsolete.

helm-bibte used it when it refactored the "helm" part off into a module, to support different backend other than helm. As a result, most helm-bibtex- prefixes are changed to bibtex-completion- ones. But they want the end user's configuration will not break, and at the same time warn them to update to the new name. Here's the code, and the last line is what actually uses the function. The actual effect is the user's configuration will be marked as warning, the mini-buffer will describe the obsolete detail.

(cl-loop
 for var in '("bibliography" "library-path" "pdf-open-function"
              "pdf-symbol" "format-citation-functions" "notes-path"
              "notes-template-multiple-files"
              "notes-template-one-file" "notes-key-pattern"
              "notes-extension" "notes-symbol" "fallback-options"
              "browser-function" "additional-search-fields"
              "no-export-fields" "cite-commands"
              "cite-default-command"
              "cite-prompt-for-optional-arguments"
              "cite-default-as-initial-input" "pdf-field")
 for oldvar = (intern (concat "helm-bibtex-" var))
 for newvar = (intern (concat "bibtex-completion-" var))
 do
 (defvaralias newvar oldvar)
 (make-obsolete-variable oldvar newvar "2016-03-20"))