When using bash `$()` command substitution doesn't work but backticks do

[kojustin]

Using tup 0.7.5 on ubuntu, I can't seem to get bash command substitution using $() to work while back ticks work correctly. When

$ ls -l
total 4
-rw-rw-r-- 1 ubuntu ubuntu 105 Jun 10 23:42 Tupfile
$ cat Tupfile
: |> ^b^ echo `cat Tupfile` > %o |> Tupfile.backup

: |> ^b^ echo $(cat Tupfile) > %o |> Tupfile.backup2
$ tup
[ tup ] [0.000s] Scanning filesystem...
tup warning: generated file 'Tupfile.backup' was deleted outside of tup. This file may be re-created on the next update.
tup warning: generated file 'Tupfile.backup2' was deleted outside of tup. This file may be re-created on the next update.
[ tup ] [0.005s] Reading in new environment variables...
[ tup ] [0.005s] No Tupfiles to parse.
[ tup ] [0.005s] No files to delete.
[ tup ] [0.005s] Executing Commands...
 1) [0.033s] echo `cat Tupfile` > Tupfile.backup
 2) [0.033s] echo  > Tupfile.backup2
 [  ] 100%
[ tup ] [0.046s] Updated.

The $() command substitution in the rule body appears to be evaluated to an empty string even before it's passed to bash.

I'm definitely using bash and bash definitely supports this syntax.

$ echo $(cat Tupfile)
: |> ^b^ echo `cat Tupfile` > %o |> Tupfile.backup : |> ^b^ echo $(cat Tupfile) > %o |> Tupfile.backup2
$ echo $SHELL
/bin/bash

I checked and it looks like /usr/bin/env bash should be returning the right shell version as well.

[gittup]

The $ character is used for variables in the Tupfile, so you need to escape it if you want it to be present in the actual command string. Eg:

: |> ^b^ echo \$(cat Tupfile) > %o |> Tupfile.backup2

[kojustin]

Is that the same as the original rule?

How do I escape a character? I looked through the man page and I didn't see any mention of escaping. I tried $$ like Make but that didn't work.

[gittup]

Oops, the escape sequence uses a backslash, but that got eaten by the markup or whatever. I've updated the previous comment to put it in a code section so you can see the backslash. Hope that helps!

[kojustin]

Cool thanks, that works! Is this worth updating the docs for? Is the man page tup.1? I'm not sure where http://gittup.org/tup/manual.html ends up coming from. Is it generated from man page?