cat_and_follow

#!/bin/bash

if [[ -z "$1" || "$1" == "--help" ]]; then
    echo "Ouput content of the file being appended to to stdout, continue outputting as more data appears in the file, exit when no processes write to the file for a while."
    echo "Usage: cat_and_follow file | something"
    exit 1
fi

F="$1"

THISPID=$$

(
    lsof -Fa  -r 2 "$F" | perl -ne 'INIT{$wd=0;} $wd=0 if /^aw/; if(/^m/) { exit 0 if $wd > 2; ++$wd; }'
    kill $THISPID;
)&

exec tail -n +1 -f "$F"