1#!/usr/local/bin/perl
2#
3# watch_a_file.perl -- use lsof -F output to watch a specific file
4#		       (or file system)
5#
6# usage:	watch_a_file.perl file_name
7
8## Interrupt handler
9
10sub interrupt { wait; print "\n"; exit 0; }
11
12
13## Start main program
14
15$Pn = "watch_a_file";
16# Check file argument.
17
18if ($#ARGV != 0) { print "$#ARGV\n"; die "$Pn usage: file_name\n"; }
19$fnm = $ARGV[0];
20if (! -r $fnm) { die "$Pn: can't read $fnm\n"; }
21
22# Do setup.
23
24$RPT = 15;				# lsof repeat time
25$| = 1;					# unbuffer output
26$SIG{'INT'} = 'interrupt';		# catch interrupt
27
28# Set path to lsof.
29
30if (($LSOF = &isexec("../lsof")) eq "") {	# Try .. first
31    if (($LSOF = &isexec("lsof")) eq "") {	# Then try . and $PATH
32	print "can't execute $LSOF\n"; exit 1
33    }
34}
35
36# Read lsof -nPF output from a pipe and gather the PIDs of the processes
37# and file descriptors to watch.
38
39open(P, "$LSOF -nPFpf $fnm|") || die "$Pn: can't pipe to $LSOF\n";
40
41$curpid = -1;
42$pids = "";
43while (<P>) {
44    chop;
45    if (/^p(.*)/) { $curpid = $1; next; }	# Identify process.
46    if (/^f/) {
47	if ($curpid > 0) {
48	    if ($pids eq "") { $pids = $curpid; }
49	    else { $pids = $pids . "," . $curpid; }
50	    $curpid = -1;
51	}
52    }
53}
54close(P);
55wait;
56if ($pids eq "") { die "$Pn: no processes using $fnm located.\n"; }
57print "watch_file: $fnm being used by processes:\n\t$pids\n\n";
58
59# Read repeated lsof output from a pipe and display.
60
61$pipe = "$LSOF -ap $pids -r $RPT $fnm";
62open(P, "$pipe|") || die "$Pn: can't pipe: $pipe\n";
63
64while (<P>) { print $_; }
65close(P);
66print "$Pn: unexpected EOF from \"$pipe\"\n";
67exit 1;
68
69
70## isexec($path) -- is $path executable
71#
72# $path   = absolute or relative path to file to test for executabiity.
73#	    Paths that begin with neither '/' nor '.' that arent't found as
74#	    simple references are also tested with the path prefixes of the
75#	    PATH environment variable.
76
77sub
78isexec {
79    my ($path) = @_;
80    my ($i, @P, $PATH);
81
82    $path =~ s/^\s+|\s+$//g;
83    if ($path eq "") { return(""); }
84    if (($path =~ m#^[\/\.]#)) {
85	if (-x $path) { return($path); }
86	return("");
87    }
88    $PATH = $ENV{PATH};
89    @P = split(":", $PATH);
90    for ($i = 0; $i <= $#P; $i++) {
91	if (-x "$P[$i]/$path") { return("$P[$i]/$path"); }
92    }
93    return("");
94}
95