If you do a regular expression search for ^word$, you would find instances of word on a line by itself. The ^ says that the w must be the first character on the line, the $ says that the d must be the last character.
If you wanted to find all words starting with beg and ending with the letter s, you could use beg[a-z]*s as your regular expression. This would find the words begins, begets, and begonias, in addition to really odd words like shibegrees and altbegaslia. If you don't want these mutants—that is, if you really want words that begin with beg and end with s, use \<beg[a-z]*s\>. The \< is a special sequence that matches the beginning of a word; \> matches the end of a word. If you wanted to find the words beg, big, and bag; but not begonias, and certainly not any strange words with beg on the inside, you would use \<b[a-z]g\> as the regular expression.
To search for a ^, $, ., *, [, ], or any number of other special characters, you obviously can't use the character itself. Put a backslash (\) first—i.e., to search for a period, search for \. For example, to search for the electronic mail address`:
howie@mcds.com
the regular expression would be:
howie@mcds\.com
This is a barebones introduction to regular expressions; see Chapter 11 for more details and Mastering Regular Expressions by Jeffrey Friedl (O'Reilly) for a book-length treatment of this topic.
You can use regular expressions in incremental searches and in query-replace. Table 3-5 lists the commands you use for regular expression searches. Although they are initiated with slightly different commands, the searches are the same as those described earlier in this chapter.
Table 3-5. Regular expression search commands
| Keystrokes | Command name | Action |
|---|---|---|
| C-M-s Enter Edit → Search → Regexp Forward | re-search-forward | Search for a regular expression forward. |
| C-M-r Enter Edit → Search → Regexp Backwards | re-search-backward | Search for a regular expression backward. |
| C-M-s Edit → Search → Incremental Search → Forward Regexp | isearch-forward-regexp | Search incrementally forward for a regular expression. |
| C-M-r Edit → Search → Incremental Search → Backward Regexp | isearch-backward-regexp | Search incrementally backward for a regular expression. |
| C-M-% Edit → Replace → Replace Regexp | query-replace-regexp | Query-replace a regular expression. |
| (none) | replace-regexp | Globally replace a regular expression unconditionally (use with caution). |
3.3 Checking Spelling Using Ispell
Emacs includes two spell-checking interfaces: to the Unix spell checker, spell, and to Ispell, which many people, including us, prefer. We say "interfaces" because Emacs does not include the executables for either of these spell-checkers. Because Ispell is superior and runs on a variety of platforms, we'll cover only Ispell here. If you attempt to run Ispell and it is not available, you'll have to install it. Chapter 13 provides details on installing Ispell on Windows and on Mac OS X.
A further enhancement to Ispell is Flyspell, a command that highlights misspelled words on the fly. If you have Ispell installed, you'll have Flyspell support as well.
3.3.1 Checking a Buffer
Ispell includes options to check a buffer, a region, the comments in a program, or a single word. After you type the command telling Ispell what area you want to check, it works the same way for all these options. We'll describe ispell-buffer here. If all the words are spelled correctly, Ispell displays the message, Spell-checking done. If Ispell finds a misspelled word, a screen like the following appears. Let's spell-check a hastily typed passage from Homer's Odyssey.