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This is an excerpt from the latest version perlfaq5.pod, which
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5.4: How can I use Perl's "-i" option from within a program?

"-i" sets the value of Perl's $^I variable, which in turn affects the
behavior of "<>"; see perlrun for more details. By modifying the
appropriate variables directly, you can get the same behavior within a
larger program. For example:

# ...
local($^I, @ARGV) = ('.orig', glob("*.c"));
while (<>) {
if ($. == 1) {
print "This line should appear at the top of each file\n";
s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case
close ARGV if eof; # Reset $.
# $^I and @ARGV return to their old values here

This block modifies all the ".c" files in the current directory, leaving
a backup of the original data from each file in a new ".c.orig" file.


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