... can I do in-place file substitution from inside a script
If using the feature behind the -i option from within a
script is what you mean... yes, you can. You can either put the
-i.bak on the shebang line, or set the corresponding $^I
special variable (as olus already mentioned). The latter allows a
little more flexibility, e.g. you could localise the effects
#!/usr/bin/perl
use strict;
use warnings;
sub edit_inplace {
local @ARGV = @_;
local $^I = ".bak";
# local $^I = ""; # no backup file
while (<>) {
s/(.*)/$1\n****************/;
print $_;
}
}
edit_inplace("test.txt");
BTW, even Perl doesn't do a real in-place edit (i.e. modify the
physically-same file). Rather, it opens, then renames (or
unlinks, when no backup extension is specified) the original
file, then opens a new file with the same name — at
least on Unix, where opened files continue to be accessible, even when
they're no longer associated with a directory entry (look at the
inode numbers before and after to verify, e.g. with "ls -li").
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