svn commit: r213082 - stable/7/bin/expr
Jilles Tjoelker
jilles at FreeBSD.org
Thu Sep 23 19:21:49 UTC 2010
Author: jilles
Date: Thu Sep 23 19:21:49 2010
New Revision: 213082
URL: http://svn.freebsd.org/changeset/base/213082
Log:
MFC r212390: expr(1): Add sh(1) versions of examples, remove an incorrect
example.
The three examples are better done using sh(1) itself these days.
The example
expr -- "$a" : ".*"
is incorrect in the general case, as "$a" may be an operator.
Modified:
stable/7/bin/expr/expr.1
Directory Properties:
stable/7/bin/expr/ (props changed)
Modified: stable/7/bin/expr/expr.1
==============================================================================
--- stable/7/bin/expr/expr.1 Thu Sep 23 18:55:54 2010 (r213081)
+++ stable/7/bin/expr/expr.1 Thu Sep 23 19:21:49 2010 (r213082)
@@ -30,7 +30,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 12, 2004
+.Dd September 9, 2010
.Dt EXPR 1
.Os
.Sh NAME
@@ -217,6 +217,9 @@ command, one might rearrange the express
More generally, parenthesize possibly-negative values:
.Dl "a=$(expr \e( $a \e) + 1)"
.It
+With shell arithmetic, no escaping is required:
+.Dl "a=$((a + 1))"
+.It
This example prints the filename portion of a pathname stored
in variable
.Va a .
@@ -229,6 +232,12 @@ The
.Li //
characters resolve this ambiguity.
.Dl "expr \*q//$a\*q \&: '.*/\e(.*\e)'"
+.It
+With modern
+.Xr sh 1
+syntax,
+.Dl "\*q${a##*/}\*q"
+expands to the same value.
.El
.Pp
The following examples output the number of characters in variable
@@ -237,19 +246,21 @@ Again, if
.Va a
might begin with a hyphen, it is necessary to prevent it from being
interpreted as an option to
-.Nm .
+.Nm ,
+and
+.Va a
+might be interpreted as an operator.
.Bl -bullet
.It
-If the
-.Nm
-command conforms to
-.St -p1003.1-2001 ,
-this is simple:
-.Dl "expr -- \*q$a\*q \&: \*q.*\*q"
-.It
-For portability to older systems, however, a more complicated command
+To deal with all of this, a complicated command
is required:
.Dl "expr \e( \*qX$a\*q \&: \*q.*\*q \e) - 1"
+.It
+With modern
+.Xr sh 1
+syntax, this can be done much more easily:
+.Dl "${#a}"
+expands to the required number.
.El
.Sh SEE ALSO
.Xr sh 1 ,
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