+=head1 NON-INTERACTIVE EDITING
+
+C<virt-edit> normally calls out to C<$EDITOR> (or vi) so
+the system administrator can interactively edit the file.
+
+There are two ways also to use C<virt-edit> from scripts in order to
+make automated edits to files. (Note that although you I<can> use
+C<virt-edit> like this, it's less error-prone to write scripts
+directly using the libguestfs API and Augeas for configuration file
+editing.)
+
+The first method is to temporarily set C<$EDITOR> to any script or
+program you want to run. The script is invoked as C<$EDITOR tmpfile>
+and it should update C<tmpfile> in place however it likes.
+
+The second method is to use the C<-e> parameter of C<virt-edit> to run
+a short Perl snippet in the style of L<sed(1)>. For example to
+replace all instances of C<foo> with C<bar> in a file:
+
+ virt-edit domname filename -e 's/foo/bar/'
+
+The full power of Perl regular expressions can be used (see
+L<perlre(1)>). For example to delete root's password you could do:
+
+ virt-edit domname /etc/passwd -e 's/^root:.*?:/root::/'
+
+What really happens is that the snippet is evaluated as a Perl
+expression for each line of the file. The line, including the final
+C<\n>, is passed in C<$_> and the expression should update C<$_> or
+leave it unchanged.
+
+To delete a line, set C<$_> to the empty string. For example, to
+delete the C<apache> user account from the password file you can do:
+
+ virt-edit mydomain /etc/passwd -e '$_ = "" if /^apache:/'
+
+To insert a line, prepend or append it to C<$_>. However appending
+lines to the end of the file is rather difficult this way since there
+is no concept of "last line of the file" - your expression just
+doesn't get called again. You might want to use the first method
+(setting C<$EDITOR>) if you want to do this.
+
+The variable C<$lineno> contains the current line number.
+As is traditional, the first line in the file is number C<1>.
+
+The return value from the expression is ignored, but the expression
+may call C<die> in order to abort the whole program, leaving the
+original file untouched.
+
+Remember when matching the end of a line that C<$_> may contain the
+final C<\n>, or (for DOS files) C<\r\n>, or if the file does not end
+with a newline then neither of these. Thus to match or substitute
+some text at the end of a line, use this regular expression:
+
+ /some text(\r?\n)?$/
+
+Alternately, use the perl C<chomp> function, being careful not to
+chomp C<$_> itself (since that would remove all newlines from the
+file):
+
+ my $m = $_; chomp $m; $m =~ /some text$/
+
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