I have a file one_liner_wrapper.pl that contains the following:

#!/usr/bin/perl -w
use strict;

my $num_subs = `perl -w -0777 -pi -e 'my $c=s/foo/bar/g;print STDOUT "
+$c\n"' ./foo_test`;

printf("num_subs = $num_subs\n");
[download]

The file foo_test contains the following:

foo
food
fool
foot
[download]

When I try to execute one_line_wrapper.pl, I receive the following error:

> ./one_liner_wrapper.pl
Global symbol "$c" requires explicit package name (did you forget to d
+eclare "my $c"?) at ./one_liner_wrapper.pl line 4.
Global symbol "$c" requires explicit package name (did you forget to d
+eclare "my $c"?) at ./one_liner_wrapper.pl line 4.
Execution of ./one_liner_wrapper.pl aborted due to compilation errors.
[download]

This error also occurs if I omit the "my " in the above code.

Why I am I receiving this error despite the "my $c" that is included at the start of the statement? If I instead change one_liner_wrapper.pl to the following:

#!/usr/bin/perl -w
use strict;

my $c;
my $num_subs = `perl -w -0777 -pi -e '$c=s/foo/bar/g;print STDOUT "$c\
+n"' ./foo_test`;

printf("num_subs = $num_subs\n");
[download]

The output is:

> ./one_liner_wrapper.pl
Use of uninitialized value $c in concatenation (.) or string at ./one_
+liner_wrapper.pl line 5.
Use of uninitialized value $c in concatenation (.) or string at ./one_
+liner_wrapper.pl line 5.
num_subs =
[download]

What is the proper way to declare variables that will be used only within perl one-liners called from another perl script when "use strict" is in effect?

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