Книга: Learning GNU Emacs, 3rd Edition

3.2.6 Regular Expressions for Search and Replacement Operations

3.2.6 Regular Expressions for Search and Replacement Operations

Sometimes none of the simpler searches described in this chapter are adequate. Regular expressions allow you to build searches with strings that contain various wildcards.

Table 3-4 shows some of the characters you can use in creating a regular expression.

Table 3-4. Characters for creating regular expressions

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`:

[email protected]

the regular expression would be:

[email protected]

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

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