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st: RE: r(198) error with a foreach loop - problem with '`'

From   "Nick Cox" <>
To   <>
Subject   st: RE: r(198) error with a foreach loop - problem with '`'
Date   Thu, 29 Apr 2010 12:25:17 +0100

This is the back-stabbing backslash problem. Stata is confused by the backslash which has two interpretations, as a delimiter and an escape character. Use forward slashes and the problem should go away. In fact only the last need be changed: 

use Work\Datasets\Source/`w'youth,clear

This is documented in the manuals at [U] 18.3.11

18.3.11 Constructing Windows filenames by using macros

Stata uses the \ character to tell its parser not to expand macros. Windows uses the \ character as the directory path separator. Mostly, there is no problem using a \ in a filename. However, if you are writing a program that contains a Windows path in macro path and a filename in fname, do not assemble the final result as `path'\`fname'
because Stata will interpret the \ as an instruction to not expand `fname'. Instead, assemble the final result as `path'/`fname' Stata understands / as a directory separator on all platforms.

And in  

SJ-8-3  pr0042  . . . . . . .  Stata tip 65: Beware the backstabbing backslash
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q3/08   SJ 8(3):446--447                                 (no commands)
        tip to use forward slash instead of backslash for
        directory and file names


Jamie Fagg

Firstly, thanks to Nick Cox and Austin Nichols for their reply to my
recent question about -esttab-. Both answers provide helpful clues to
where I should be going with the problem, but both also raised some
extra questions which I haven't had a chance to work through yet.

On a separate note, Stata is suddenly telling me that ` is not valid
in my foreach loops and I cannot work out where to look to identify
the problem. Code illustrating the issue is below.

//show that file exists
. use Work\Datasets\Source\dyouth,clear

. des, short

Contains data from Work\Datasets\Source\dyouth.dta
 obs:           773
vars:           101
size:        98,171 (99.9% of memory free)
Sorted by:

//show error with foreach loop
. foreach w in d {
 2.         use Work\Datasets\Source\`w'youth,clear
 3. }
invalid '`'

end of do-file


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