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How do I assign multiple backslash characters to macros in Stata?
Backslashes and macros
Alan Riley, StataCorp
Any explanations out there
for the following behavior? Stata seems to run into trouble assigning
multiple backslash characters to macros:
. local x1 "\"
. local x2 "\\"
. local x3 "\\\"
. local x4 "\\\\" ...
. di "[`x1']" [\]
. di "[`x2']" [\]
. di "[`x3']" [\\]
. di "[`x4']" [\\]
This behavior is by design. The backslash character is an escape character
for certain other characters.
It is sometimes necessary to prevent macro substitution. If you want to
display a macro rather than its contents, you might want to write something
. display "$myfile"
in the case of a global macro or
. display "`myfile'"
in the case of a local macro. Of course, this won’t work, as Stata
will immediately substitute the value of the “myfile” global or
local macro and display that instead.
Stata allows you to use the backslash as a protection or
“escape” character to prevent macro substitution or to allow
delayed macro substitution.
In the examples above, the proper syntax would be
. display "\$myfile" . display "\`myfile'"
to literally display
This leads to another issue. What if a user really wishes to have a
backslash in a command and still have a macro expanded after it? For
. use c:\data\`myfile'
Because the backslash is an escape character and prevents macro
substitution, Stata will literally try to read a file named
c:\data'myfile'. Therefore, the escape character must also be able
to escape itself—to tell Stata not to have it escape the opening
macro character that might follow:
. use c:\data\\`myfile'
An alternative is
to use forward slashes (/) when writing paths. Stata will interpret the
forward slash correctly as a path delimiter. For example, you could
. use c:/data/`myfile'
and avoid the
Stata’s rules on this protection are simple and consistent:
Anywhere this is typed
Stata sees this
\ (after applying the rules above)
This is why, in the examples above, every set of two backslashes
“collapsed” into a single backslash.