Bash script using 'watch' fails. Why?

I need to run repeatedly (every 3600 seconds) the following commands from the terminal:

if whois abcxyz.com | grep -q 'string'; then echo 'Message line 1' echo 'Message line 2'
fi

I tried using watch, as follows:

watch -n 3600 if whois abcxyz.com | grep -q 'string'; then echo 'Message line 1' echo 'Message line 2'
fi

but I get error messages.

Could you please help me make it work?

Thanks

1

2 Answers

Since watch [options] command executes command using sh -c by default, you can use it run snippets of shell code directly provided that:

1. you get the quoting right

and

2. your code is sh-compatible i.e. doesn't use any bash/zsh/csh-"isms"

So for example

$ watch -n 36 'if whois abcxyz.com | grep -q "string"; then echo "Message line 1" | ts echo "Message line 2" | ts
fi'

1

watch is documented (in man watch) as:

watch [options] command

It wants a simple command, not a whole command expression,
so, you have to wrap your command in a bash script, and watch that.

For example,

In $HOME/bin/foo:

#!/bin/bash
if whois abcxyz.com | grep -q 'string'; then echo 'Message line 1'
else echo 'Message line 2'
fi

Then, afer making foo executable with chmod +x $HOME/bin/foo,

watch -n 3600 $HOME/bin/foo

4

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