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author | Warner Losh <imp@FreeBSD.org> | 2020-10-13 05:19:00 +0000 |
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committer | Warner Losh <imp@FreeBSD.org> | 2020-10-13 05:19:00 +0000 |
commit | eb93b08fe07c5d396ebb920e9579accbaeaea603 (patch) | |
tree | df9d6f3a54f0d18515ee8afd5c733f883e6600c3 /sbin/devd | |
parent | e69469695644f6da23e78a6a38f5f368359ce6e6 (diff) | |
download | src-eb93b08fe07c5d396ebb920e9579accbaeaea603.tar.gz src-eb93b08fe07c5d396ebb920e9579accbaeaea603.zip |
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
Notes
Notes:
svn path=/head/; revision=366661
Diffstat (limited to 'sbin/devd')
-rw-r--r-- | sbin/devd/devd.conf.5 | 58 |
1 files changed, 57 insertions, 1 deletions
diff --git a/sbin/devd/devd.conf.5 b/sbin/devd/devd.conf.5 index 7782631e2384..80b23ec00401 100644 --- a/sbin/devd/devd.conf.5 +++ b/sbin/devd/devd.conf.5 @@ -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 , |