The '!' magic does not work when followed by non-alphabetical characters

[narensrini]

If I have a cell of the following form:

x = "echo"
!{x} "hello world"

This is valid jupyter syntax, and it prints out "foo" to stdout via a shell process.

However, the percent representation in jupytext outputs the following:

# %%
x = "echo"
!{x} "hello world"

This is incorrect - the line should be commented out in the percent syntax after recognizing the magic.

This will also fail when running bash commands that do not begin with an alphabetical character (eg. ':', '$!')

It looks like a fix that updates the regex in #819 would work here.

[Skylion007]

This seems to be an extension of the issue with #587 . The Regex needs to be expanded to include {}.

[mwouts]

This will also fail when running bash commands that do not begin with an alphabetical character (eg. ':', '$!')

@narensrini , we have changed the regex to escape the pattern !{x}, but you seem to mention other cases, would you like to give a few more examples that you'd like to see supported? Thanks