Using globs in Perl replace one liner in TCL script - tcl

Question

I want to run one Perl one liner in TCL script as below:
exec perl -i -pe {s/SUBSTRING/REPLACING_STRING/g} testFile;
This works fine. But, if I want to modify all the files like below:
exec perl -i -pe {s/SUBSTRING/REPLACING_STRING/g} *;
it gives me the error message:
Can't open '*': No such file or directory.
while executing
exec perl -i -pe {s/SUBSTRING/REPLACING_STRING/g} *;
I tried bracing the '*', but did not solve the problem. Requesting for help...

Answer 1

Assuming that the files a, b, and c are present in the current working directory, executing echo * in the shell prints a b c. This is because the shell command evaluator recognizes wildcard characters and splices in a list of zero or more file names where the wildcard expression was found.
Tcl's command evaluator does not recognize wildcard characters, but passes them unsubstituted to the command that was invoked. If that command can work with wildcards it will do so. The exec command doesn't, which means it will pass the wildcard expression as is to the shell command named by the command string.
Testing this, we get
% exec echo *
*
because what we asked the shell to execute was simply
echo *
If we want a wildcard expression expanded to a list of file names, we need an explicit call to the glob command:
% exec echo [glob *]
"a b c"
which still isn't quite right, since the list wasn't automatically spliced into the command string: instead the shell got
echo {a b c}
(Note: I’m faking echo on Windows here, the actual output might be different.)
To both expand and splice the list of file names, we need this:
% exec echo {*}[glob *]
a b c
The {*} prefix tells the Tcl command evaluator to substitute the following argument as if the words resulting from it were arguments in the original command line.
echo a b c
This example, with a more concise explanation than I've given here, is in the documentation for exec:
"If you are converting invocations involving shell globbing, you should remember that Tcl does not handle globbing or expand things into multiple arguments by default. Instead you should write things like this:"
exec ls -l {*}[glob *.tcl]
PS:
If one has loaded the fileutil package:
package require fileutil
this can be written as a one-liner in Tcl too:
foreach file [glob *] {::fileutil::updateInPlace $file {apply {str {regsub -all SUBSTRING $str REPLACING_STRING}}}}
or with line breaks and indentation for readability:
foreach file [glob *] {
::fileutil::updateInPlace $file {
apply {str {
regsub -all SUBSTRING $str REPLACING_STRING
}}
}
}
Documentation: apply, exec, fileutil package, foreach, glob, package, regsub, {*}