OS X Bash, 'watch' command
MacosBashAutomationWatchMacos Problem Overview
I'm looking for the best way to duplicate the Linux 'watch' command on Mac OS X. I'd like to run a command every few seconds to pattern match on the contents of an output file using 'tail' and 'sed'.
What's my best option on a Mac, and can it be done without downloading software?
Macos Solutions
Solution 1 - Macos
With Homebrew installed:
brew install watch
Solution 2 - Macos
You can emulate the basic functionality with the shell loop:
while :; do clear; your_command; sleep 2; done
That will loop forever, clear the screen, run your command, and wait two seconds - the basic watch your_command
implementation.
You can take this a step further and create a watch.sh
script that can accept your_command
and sleep_duration
as parameters:
#!/bin/bash
# usage: watch.sh <your_command> <sleep_duration>
while :;
do
clear
date
$1
sleep $2
done
Solution 3 - Macos
Use MacPorts:
$ sudo port install watch
Solution 4 - Macos
The shells above will do the trick, and you could even convert them to an alias (you may need to wrap in a function to handle parameters):
alias myWatch='_() { while :; do clear; $2; sleep $1; done }; _'
Examples:
myWatch 1 ls ## Self-explanatory
myWatch 5 "ls -lF $HOME" ## Every 5 seconds, list out home directory; double-quotes around command to keep its arguments together
Alternately, Homebrew can install the watch from http://procps.sourceforge.net/:
brew install watch
Solution 5 - Macos
It may be that "watch" is not what you want. You probably want to ask for help in solving your problem, not in implementing your solution! :)
If your real goal is to trigger actions based on what's seen from the tail
command, then you can do that as part of the tail itself. Instead of running "periodically", which is what watch
does, you can run your code on demand.
#!/bin/sh
tail -F /var/log/somelogfile | while read line; do
if echo "$line" | grep -q '[Ss]ome.regex'; then
# do your stuff
fi
done
Note that tail -F
will continue to follow a log file even if it gets rotated by newsyslog or logrotate. You want to use this instead of the lower-case tail -f
. Check man tail
for details.
That said, if you really do want to run a command periodically, the other answers provided can be turned into a short shell script:
#!/bin/sh
if [ -z "$2" ]; then
echo "Usage: $0 SECONDS COMMAND" >&2
exit 1
fi
SECONDS=$1
shift 1
while sleep $SECONDS; do
clear
$*
done
Solution 6 - Macos
I am going with the answer from here:
bash -c 'while [ 0 ]; do <your command>; sleep 5; done'
But you're really better off installing watch as this isn't very clean...
Solution 7 - Macos
If watch doesn't want to install via
brew install watch
There is another similar/copy version that installed and worked perfectly for me
brew install visionmedia-watch
Solution 8 - Macos
Or, in your ~/.bashrc file:
function watch {
while :; do clear; date; echo; $@; sleep 2; done
}
Solution 9 - Macos
To prevent flickering when your main command takes perceivable time to complete, you can capture the output and only clear screen when it's done.
function watch {while :; do a=$($@); clear; echo "$(date)\n\n$a"; sleep 1; done}
Then use it by:
watch istats
Solution 10 - Macos
Try this:
#!/bin/bash
# usage: watch [-n integer] COMMAND
case $# in
0)
echo "Usage $0 [-n int] COMMAND"
;;
*)
sleep=2;
;;
esac
if [ "$1" == "-n" ]; then
sleep=$2
shift; shift
fi
while :;
do
clear;
echo "$(date) every ${sleep}s $@"; echo
$@;
sleep $sleep;
done
Solution 11 - Macos
Here's a slightly changed version of this answer that:
- checks for valid args
- shows a date and duration title at the top
- moves the "duration" argument to be the 1st argument, so complex commands can be easily passed as the remaining arguments.
To use it:
- Save this to
~/bin/watch
- execute
chmod 700 ~/bin/watch
in a terminal to make it executable. - try it by running
watch 1 echo "hi there"
~/bin/watch
#!/bin/bash
function show_help()
{
echo ""
echo "usage: watch [sleep duration in seconds] [command]"
echo ""
echo "e.g. To cat a file every second, run the following"
echo ""
echo " watch 1 cat /tmp/it.txt"
exit;
}
function show_help_if_required()
{
if [ "$1" == "help" ]
then
show_help
fi
if [ -z "$1" ]
then
show_help
fi
}
function require_numeric_value()
{
REG_EX='^[0-9]+$'
if ! [[ $1 =~ $REG_EX ]] ; then
show_help
fi
}
show_help_if_required $1
require_numeric_value $1
DURATION=$1
shift
while :; do
clear
echo "Updating every $DURATION seconds. Last updated $(date)"
bash -c "$*"
sleep $DURATION
done
Solution 12 - Macos
Use the Nix package manager!
Install Nix, and then do nix-env -iA nixpkgs.watch
and it should be available for use after the completing the install instructions (including sourcing . "$HOME/.nix-profile/etc/profile.d/nix.sh"
in your shell).