Suppose you need to do find/replace of a string pattern, for the hundreds of files in a directory. However, you do not want to replace all of them. You need to look at it in a case-by-case basis. What can you do?
diredto list files in dir, or call
find-diredif you need all subdirectories.
ibufferto list all opened files.
Start emacs by typing “emacs” in the command line interface prompt. (Or, double click the Emacs icon if you are in a Graphics User Interface environment)
First you need to select the files you want to do the replace. Use the graphical menu 〖File ▸ Open Directory〗. Emacs will ask you for a directory path. Type the directory path, then press Enter.
Now, you will be shown the list of files, and now you need to mark the files you want the regex find/replace to work on. You mark a file by moving the cursor to the file you want, then press m. Unmark it by pressing u. (To list subdirectories, move your cursor to the directory and press i. The sub-directory's content will be listed at the bottom.) To mark all files by a regex, type 【% m】, then type your regex pattern. For example, if you want to mark all HTML files, then type 【% m】 then
(You can find a list of the mark commands in the graphical menu “Mark” (this menu appears when you are in the dired mode).)
If you want to do find/replace on files inside a directory, including hundreds of subdirectories, here's a method to select all these files.
find-dired. (you call a command by pressing 【Alt+x】) Then, type a directory name, ⁖ 〔/Users/mary/myfiles〕
Note: if you are using emacs on a unix non-graphical text terminal, and if 【Alt+x】 does not work, the equivalent key stroke is 【Esc x】.
Emacs will ask you with the prompt “Run find (with args): ”. If you need to do the replacement on all HTML files, then type
-name "*html". If you don't care about what kind of file but simply all files under that dir, then give “-type f”.
Now, mark the files as described above.
Now, you are ready to do the interactive find replace. For simplicity, let's say you just want to replace the word “quick” by “super”. Now, call
dired-do-query-replace-regexp. It will prompt you for the regex string and the replacement string. Type “quick”, enter, then “super”.
Now, emacs will use your pattern and check the files, and stop and show you whenever a match occurred. When this happens, emacs will prompt you, and you have a choice of making the change or skip the change. To make the change, type y. To skip, type n. If you simply want emacs to go ahead and make all such changes to the current file, type !.
If you want to cancel the whole operation without saving any changes you've made, type 【Ctrl+g】, then exit emacs using the menu 〖File ▸ Exit Emacs〗.
Now, after you went through the above ordeal, there is one more step you need to do, and that is saving the changed files.
If you are using emacs version 22 or later, then call
ibuffer to go into a buffer listing mode, then type 【* u】 to mark all unsaved files, then type S to save them all. (that's shift-s)
If you are using a emacs version 21, then you can do this: call
list-buffers, then move the cursor to the file you want to save and type s. It will mark the file for later save action. Type u to unmark. Once you are done, type x to execute the saving of all files marked for save. (in emacs, opened file is called “buffer”. Disregard other things there.)
Alternative to the above options, you can also call
save-some-buffers 【Ctrl+x s】. Then emacs will display each unsaved file and ask if you want it saved.
Note: emacs's regex is not the same as Perl or Python's, but similar. For a summary and common patterns, see: Emacs Regex.