exec.3: Rewrite description of PATH and mention _CS_PATH

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/exec.3

@@ -36,7 +36,7 @@
 .\" Modified, 24 Jun 2004, Michael Kerrisk <mtk.manpages@gmail.com>
 .\"     Added note on casting NULL
 .\"
-.TH EXEC 3  2009-02-22 "GNU" "Linux Programmer's Manual"
+.TH EXEC 3  2010-09-23 "GNU" "Linux Programmer's Manual"
 .SH NAME
 execl, execlp, execle, execv, execvp \- execute a file
 .SH SYNOPSIS
@@ -121,17 +121,24 @@ image from the external variable
 in the current process.
 .SS Special semantics for execlp() and execvp()
 .PP
-The functions
+The
 .BR execlp ()
 and
 .BR execvp ()
-will duplicate the actions of the shell in searching for an executable file
+functions duplicate the actions of the shell in
+searching for an executable file
 if the specified filename does not contain a slash (/) character.
-The search path is the path specified in the environment by the
+The file is sought in the colon-separated list of directory pathnames
+specified in the
 .B PATH
-variable.
-If this variable isn't specified, the default path
-":/bin:/usr/bin" is used.
+environment variable.
+If this variable isn't defined, the path list defaults to
+the current directory followed by the list of directories returned by
+.IR confstr(_CS_PATH) .
+(This
+.BR confstr (3)
+call typically returns the value "/bin:/usr/bin".)
+
 In addition, certain
 errors are treated specially.
 .PP