Author: imp Date: Tue Oct 13 05:19:00 2020 New Revision: 366661 URL: https://svnweb.freebsd.org/changeset/base/366661
Log: Document the rather suprising behavior with ' inside action rules. To prevent issues with odd shell characters appearing in, a surprising shell feature is used. Document it and a workaround for it. Differential Revision: https://reviews.freebsd.org/D26723 Modified: head/sbin/devd/devd.conf.5 Modified: head/sbin/devd/devd.conf.5 ============================================================================== --- head/sbin/devd/devd.conf.5 Tue Oct 13 04:37:57 2020 (r366660) +++ head/sbin/devd/devd.conf.5 Tue Oct 13 05:19:00 2020 (r366661) @@ -40,7 +40,7 @@ .\" ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS .\" SOFTWARE. .\" -.Dd August 18, 2020 +.Dd October 12, 2020 .Dt DEVD.CONF 5 .Os .Sh NAME @@ -662,6 +662,59 @@ For example: // is a new comment, even though it is logically // part of the previous comment. .Ed +.Ss Notes on Variable Expansion +To prevent issues with special shell characters, the following happens for each +variable +.Ic $foo . +.Bl -enum +.It +The characters +.Dq $' +are inserted. +.It +The string +.Dq $foo +is removed. +.It +The value of the +.Ic foo +variable is inserted into the buffer with all single quote characters +prefixed by a backslash. +.El +.Pp +See +.Xr sh 1 +for what this construct means. +It is safe in all context, except one: inside single quotes. +If foo=meta and bar=var, then a rule like the following: +.Bd -literal -offset indent -compact +action "echo '$foo $bar'"; +.Ed +will be presented to the shell via +.Xr system 3 +as +.Bd -literal -offset indent -compact +echo '$'meta' $'var'' +.Ed +which produces the following output: +.Bd -literal -offset indent -compact +$meta $var +.Ed +as its output. +This is an unanticipated result. +A future version of this software will change this behavior. +Users are discouraged from using single quotes inside +.Ic action +value without due care. +.Pp +The above should be written as +.Bd -literal -offset indent -compact +action "echo $foo' '$bar" +.Ed +to produce a single argument to echo. +Given the above expansion, juxtaposing bare variables with +single quote expressions will produce the right output, +regardless of the value of the variable. .Sh FILES .Bl -tag -width ".Pa /etc/devd.conf" -compact .It Pa /etc/devd.conf @@ -733,6 +786,9 @@ detach 0 { The installed .Pa /etc/devd.conf has many additional examples. +.Sh BUGS +The variable expansion's interaction with single quotes is +suboptimal and surprising. .Sh SEE ALSO .Xr cam 4 , .Xr coretemp 4 , _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
