13.4. Extended Searching for Text with egrepThe egrep command is yet another version of grep (Section 13.2), one that extends the syntax of regular expressions. (Versions where grep and egrep are the same allow you to get egrep-like behavior from grep by using the -E option.) A plus sign (+) following a regular expression matches one or more occurrences of the regular expression; a question mark (?) matches zero or one occurrences. In addition, regular expressions can be nested within parentheses: % egrep "Lab(oratorie)?s" name.list AT&T Bell Laboratories AT&T Bell Labs Symtel Labs of Chicago Parentheses surround a second regular expression and ? modifies this expression. The nesting helps to eliminate unwanted matches; for instance, the word Labors or oratories would not be matched. Another special feature of egrep is the vertical bar (|), which serves as an or operator between two expressions. Lines matching either expression are printed, as in the next example: % egrep "stdscr|curscr" ch03 into the stdscr, a character array. When stdscr is refreshed, the stdscr is refreshed. curscr. initscr( ) creates two windows: stdscr and curscr. Remember to put the expression inside quotation marks to protect the vertical bar from being interpreted by the shell as a pipe symbol. Look at the next example: % egrep "Alcuin (User|Programmer)('s)? Guide" docguide Alcuin Programmer's Guide is a thorough refer to the Alcuin User Guide Alcuin User's Guide introduces new users to You can see the flexibility that egrep's syntax can give you, matching either User or Programmer and matching them regardless of whether they had an 's. Both egrep and fgrep can read search patterns from a file using the -f option (Section 13.5). -- DJPD Copyright © 2003 O'Reilly & Associates. All rights reserved. |
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