entr.1

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.\" Copyright (c) 2012 Eric Radman <ericshane@eradman.com>
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.Dd February 2, 2024
.Dt ENTR 1
.Os
.Sh NAME
.Nm entr
.Nd run arbitrary commands when files change
.Sh SYNOPSIS
.Nm
.Op Fl acdnprsxz
.Ar utility
.Op Ar argument /_ ...
.Sh DESCRIPTION
A list of files provided on standard input, and the
.Ar utility
is executed using the supplied arguments if any of them change.
.Nm
waits for the child process to finish before responding to subsequent file
system events.
A TTY is also opened before entering the watch loop in order to support
interactive utilities.
.Pp
The arguments are as follows:
.Bl -tag -width Ds
.It Fl a
Respond to all events which occur while the
.Ar utility
is running.
Without this option,
.Nm
consolidates events in order to avoid looping.
This option has no effect in conjunction with the
.Fl r
flag.
.It Fl c
Clear the screen before invoking the
.Ar utility
specified on the command line.
Specify twice to erase the scrollback buffer.
.It Fl d
Track the directories of regular files provided as input and exit if a new file
is added.
This option also enables directories to be specified explicitly.
If specified twice, all new entries to a directory are recognized,
otherwise files with names beginning with
.Ql \&.
are ignored.
.It Fl n
Run in non-interactive mode.
In this mode
.Nm entr
does not attempt to read from the TTY or change its properties.
.It Fl p
Postpone the first execution of the
.Ar utility
until a file is modified.
.It Fl r
Reload a persistent child process.
As with the standard mode of operation, a
.Ar utility
which terminates is not executed again until a file system or keyboard event is
processed.
.Dv SIGTERM
is used to terminate the
.Ar utility
before it is restarted.
A process group is created to prevent shell scripts from masking signals.
.Nm
waits for the
.Ar utility
to exit to ensure that resources such as sockets have been closed.
Control of the TTY is not transferred to the child process.
.It Fl s
Evaluate the first argument using the interpreter specified by the
.Ev SHELL
environment variable.
.It Fl x
Format custom exit status messages using a persistent
.Xr awk 1
process.
The path to the status script is defined by the environment variable
.Ev ENTR_STATUS_SCRIPT .
If the status script does not exist,
.Nm
will create an example.
Shell commands and file redirection is not permitted by default, but may be
enabled by specifying
.Fl x
twice.
.It Fl z
Exit after the
.Ar utility
completes.
When combined with
.Fl r
the
.Ar utility
will be restarted again only in response to commands or file system
events.
.El
.Pp
The first argument named
.Ar /_
is replaced with the absolute path of the first file to trigger an event.
The first file under watch is used as the default.
If the
.Fl s
option is used, the name of the first file to trigger an event can be read from
.Va $0 .
.Sh COMMANDS
.Nm
listens for keyboard input and responds to the following commands:
.Bl -tag -width <space>
.It Aq Cm space
Execute the utility immediately.
If the
.Fl Cm r
option is set this will terminate and restart the child process as if a file
change event had occurred.
.It Cm q
Quit; equivalent pressing
.Aq Cm control-C .
.El
.Sh ENVIRONMENT
.Bl -tag -width "ENTR_ENVIRON"
.It Ev ENTR_STATUS_SCRIPT
The path to the exit status script enabled by the
.Fl x
option.
By default
.Pa $HOME/.entr/status.awk
is evaluated.
.It Ev PAGER
Set to
.Pa /bin/cat
by default
to prevent interactive utilities from waiting for keyboard input if output does
not fit on the screen.
.It Ev SHELL
Specify the shell to use with the
.Fl s
flag.
The default is
.Pa /bin/sh .
.It Ev EV_TRACE
Print file system event messages.
.El
.Sh EXIT STATUS
If the
.Fl z
flag is set and the
.Ar utility
is successfully executed, the status of the child process is returned.
If the child process was terminated by a signal, the exit status is the signal
number plus 128.
.Pp
.Nm
normally returns one of the following values:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It 0
Normal termination after receiving
.Dv SIGINT
.It 1
No regular files were provided as input or an error occurred
.It 2
A file was added to a directory and the directory watch option was specified
.El
.Sh EXAMPLES
Rebuild a project if source files change, limiting output to the first 20 lines:
.Pp
.Dl $ find src/ | entr -s 'make | head -n 20'
.Pp
Launch and auto-reload a node.js server:
.Pp
.Dl $ ls *.js | entr -r node app.js
.Pp
Clear the screen and run a query after the SQL script is updated:
.Pp
.Dl $ echo my.sql | entr -cp psql -f /_
.Pp
Rebuild project if a source file is modified or added to the src/ directory:
.Pp
.Dl $ while sleep 0.1; do ls src/*.rb | entr -d make; done
.Pp
Auto-reload a web server, or terminate if the server exits
.Pp
.Dl $ ls * | entr -rz ./httpd