```{index} single: Filter::tee ``` # Filter::tee ```{pperl-module-badges} Filter::tee ``` Copies the source that follows `use Filter::tee` to a file, as the compiler reads it. ## Synopsis ```perl use Filter::tee 'filename'; # empty the file first, then write use Filter::tee '>filename'; # the same use Filter::tee '>>filename'; # append ``` ## How it works `import` opens the file and installs a source filter. Each time the compiler reads more of the file being compiled, the filter passes the text on unchanged and writes a copy of it to the file; at the end of the source it closes the file and removes itself. Used after another filter (`use Filter::decrypt; use Filter::tee ...`), it copies what that filter produced, which is what makes it a debugging aid for filters. This is a native implementation of `tee.xs` of Filter 1.65; its `Filter/tee.pm` is used unchanged. ## Differences from upstream None.