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| author |   jmc <jmc@openbsd.org> | 2003-12-22 12:01:41 +0000 |
|---|---|---|
| committer | jmc <jmc@openbsd.org> | 2003-12-22 12:01:41 +0000 |
| commit | 2f371dd00fd9896c386ab5de64cdb7f1401b1301 (patch) | |
| tree | af3326eb7ca4d535d0ecea4180f8af44031f05f0 | |
| parent | Correctly handle vme attachments which specify a larger ca_len size than (diff) | |
| download | wireguard-openbsd-2f371dd00fd9896c386ab5de64cdb7f1401b1301.tar.xz wireguard-openbsd-2f371dd00fd9896c386ab5de64cdb7f1401b1301.zip | |
document matching the empty string;
started by vax at carolina dot rr dot com (NetBSD PR 23810),
resolved by jdolecek@netbsd (rev. 1.24);
ok millert@
| -rw-r--r-- | bin/expr/expr.1 | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/bin/expr/expr.1 b/bin/expr/expr.1 index a7581c8ba97..44635caefa2 100644 --- a/bin/expr/expr.1 +++ b/bin/expr/expr.1 @@ -1,4 +1,4 @@ -.\" $OpenBSD: expr.1,v 1.13 2003/03/12 20:12:35 deraadt Exp $ +.\" $OpenBSD: expr.1,v 1.14 2003/12/22 12:01:41 jmc Exp $ .\" $NetBSD: expr.1,v 1.9 1995/04/28 23:27:13 jtc Exp $ .\" .\" Written by J.T. Conklin <jtc@netbsd.org>. @@ -71,6 +71,22 @@ otherwise, the matching operator returns the number of characters matched. If the match fails and the pattern contains a regular expression subexpression the null string is returned; otherwise, returns 0. +.Pp +Note: the empty string cannot be matched using +.Bd -literal -offset indent +expr '' : '$' +.Ed +.Pp +This is because the returned number of matched characters +.Pq zero +is indistinguishable from a failed match, so +.Nm +returns failure +.Pq 0 . +To match the empty string, use a structure such as: +.Bd -literal -offset indent +expr X'' : 'X$' +.Ed .El .Pp Parentheses are used for grouping in the usual manner. |