fswatch
v. 1.17.1
fswatch is a file change monitor that receives notifications when the contents
of the specified files or directories are modified. fswatch implements
several monitors:
stat (2) can be used).fswatch should build and work correctly on any system shipping either of the
aforementioned APIs.
fswatch is a frontend of libfswatch, a library with C and C++ binding. More
information on libfswatch can be found here.
fswatch main features are:
The limitations of fswatch depend largely on the monitor being used:
The FSEvents monitor, available only on macOS, has no known limitations, and scales very well with the number of files being observed.
The File Events Notification monitor, available on Solaris kernels and its derivatives, has no known limitations.
The kqueue monitor, available on any *BSD system featuring kqueue,
requires a file descriptor to be opened for every file being watched. As a
result, this monitor scales badly with the number of files being observed,
and may begin to misbehave as soon as the fswatch process runs out of file
descriptors. In this case, fswatch dumps one error on standard error for
every file that cannot be opened.
The inotify monitor, available on Linux since kernel 2.6.13, may suffer
a queue overflow if events are generated faster than they are read from the
queue. In any case, the application is guaranteed to receive an overflow
notification which can be handled to gracefully recover. fswatch
currently throws an exception if a queue overflow occurs. Future versions
will handle the overflow by emitting proper notifications.
The Windows monitor can only establish a watch directories, not files. To watch a file, its parent directory must be watched in order to receive change events for all the directory's children, recursively at any depth. Optionally, change events can be filtered to include only changes to the desired file.
The poll monitor, available on any platform, only relies on available CPU and memory to perform its task. The performance of this monitor degrades linearly with the number of files being watched.
Usage recommendations are as follows:
On macOS, use only the FSEvents monitor (which is the default behaviour).
On Solaris and its derivatives use the File Events Notification monitor.
On Linux, use the inotify monitor (which is the default behaviour).
If the number of files to observe is sufficiently small, use the kqueue
monitor. Beware that on some systems the maximum number of file descriptors
that can be opened by a process is set to a very low value (values as low as
256 are not uncommon), even if the operating system may allow a much larger
value. In this case, check your OS documentation to raise this limit on
either a per process or a system-wide basis.
If feasible, watch directories instead of files. Properly crafting the receiving side of the events to deal with directories may sensibly reduce the monitor resource consumption.
On Windows, use the windows monitor.
If none of the above applies, use the poll monitor. The authors' experience
indicates that fswatch requires approximately 150 MB of RAM memory to
observe a hierarchy of 500.000 files with a minimum path length of 32
characters. A common bottleneck of the poll monitor is disk access, since
stat()-ing a great number of files may take a huge amount of time. In
this case, the latency should be set to a sufficiently large value in order
to reduce the performance degradation that may result from frequent disk
access.
A regular user may be able to fetch fswatch from the package manager of your
OS or a third-party one. If you are looking for fswatch for macOS, you can
install it using either MacPorts or Homebrew:
# MacPorts
$ port install fswatch
# Homebrew
$ brew install fswatch
On FreeBSD, fswatch can be installed using pkg:
# pkg install fswatch-monCheck your favourite package manager and let us know if fswatch is missing
there.
A user who wishes to build fswatch should get a release tarball.
A release tarball contains everything a user needs to build fswatch on their
system, following the instructions detailed in the Installation section below
and the INSTALL file.
A developer who wishes to modify fswatch should get the sources (either from a
source tarball or cloning the repository) and have the GNU Build System
installed on their machine. Please read README.gnu-build-system to get further
details about how to bootstrap fswatch from sources on your machine.
Getting a copy of the source repository is not recommended unless you are a developer, you have the GNU Build System installed on your machine, and you know how to bootstrap it on the sources.
See the INSTALL file for detailed information about how to configure and
install fswatch. Since the fswatch builds and uses dynamic libraries, in
some platforms you may need to perform additional tasks before you can use
fswatch:
Make sure the installation directory of dynamic libraries ($PREFIX/lib) is
included in the lookup paths of the dynamic linker of your operating system.
The default path, /usr/local/lib, will work in nearly every operating
system.
Refreshing the links and cache to the dynamic libraries may be required. In
GNU/Linux systems you may need to run ldconfig:
$ ldconfig
fswatch is a C++ program and a C++ compiler compliant with the C++11 standard
is required to compile it. Check your OS documentation for information about
how to install the C++ toolchain and the C++ runtime.
No other software packages or dependencies are required to configure and install
fswatch but the aforementioned APIs used by the file system monitors.
fswatch provides the following documentation:
fswatch official documentation is provided in Texinfo format. This is the
most comprehensive source of information about fswatch and the only
authoritative one. The man page, in particular, is a stub that suggests the
user to use the info page instead.
If you are installing fswatch using a package manager and you would like the
PDF manual to be bundled into the package, please send a feature request to the
package maintainer.
fswatch is localizable and internally uses GNU gettext to decouple
localizable string from their translation. The currently available locales are:
en).it).es).To build fswatch with localization support, you need to have gettext
installed on your system. If configure cannot find libintl, then you may need to manually provide their
location to configure, usually using the CPPFLAGS and the LDFLAGS
variables. See README.macos for an example.
If gettext is not available on your system, fswatch shall build correctly,
but it will lack localization support and the only available locale will be
English.
fswatch accepts a list of paths for which change events should be received:
$ fswatch [options] ... path-0 ... path-n
The event stream is created even if any of the paths do not exist yet. If they
are created after fswatch is launched, change events will be properly
received. Depending on the watcher being used, newly created paths will be
monitored after the amount of configured latency has elapsed.
The output of fswatch can be piped to other program in order to process it
further:
$ fswatch -0 path | while read -d "" event
do
// do something with ${event}
done
To run a command when a set of change events is printed to standard output but no event details are required, then the following command can be used:
$ fswatch -o path | xargs -n1 -I{} program
The behaviour is consistent with earlier versions of fswatch (v. 0.x).
Please, read the Compatibility Issues with fswatch v. 0.x section for further
information.
By default fswatch chooses the best monitor available on the current platform,
in terms of performance and resource consumption. If the user wishes to specify
a different monitor, the -m option can be used to specify the monitor by name:
$ fswatch -m kqueue_monitor path
The list of available monitors can be obtained with the -h option.
For more information, refer to the fswatch documentation.
Everybody is welcome to contribute to fswatch. Please, see
CONTRIBUTING for further information.
Bug reports can be sent directly to the authors.
The author can be contacted on IRC, using the Freenode #fswatch channel.
This software is dual-licensed under the GPL v. 3.0 and the Apache License v. 2.0.
Copyright (c) 2013-2021 Enrico M. Crisostomo
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.
