unable to print a positional parameter in a script

Question

I'm using this method to open a Gnome terminal window and run command(s) — in this case, to send me simple notification messages (will be scheduled via at):

#!/bin/sh
gnome-terminal -- /bin/sh -c 'echo "remember: $1"; exec bash'

The shell only prints the remember: string and not my specified value, for instance when running remind.sh "pick up the package" or remind.sh "buy groceries X and Y".

When I strip the script down to its core everything works as expected (of course won't have any use in automation via cron or systemd as nothing is displayed on the foreground):

#!/bin/sh
echo "remember: $1"

Answer 1

Analysis

The code you (or rather gnome-terminal in your case) provides to /bin/sh -c will see positional parameters provided after the code. E.g. this

gnome-terminal -- /bin/sh -c 'echo "remember: $1"; exec bash' zeroth first second …

will print remember: first.

Providing nothing after the code causes $1 (or $2, $3 etc.) expand to an empty string when the code is finally interpreted ($0 is somewhat different but this doesn't matter here). This is the reason you got remember:. /bin/sh run by gnome-terminal simply knows nothing about the positional parameters of the main script, unless you pass them explicitly.

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Solution

To populate positional parameters of the inner code with positional parameters of the script, use "$@" instead of first second …:

gnome-terminal -- /bin/sh -c 'echo "remember: $1"; exec bash' sh "$@"

You can pass whatever you want. Here we pass all the parameters ("$@" expands to all positional parameters), but in general you can use "$1" (if you want the inner code to know the first parameter only) or "$2" (if you want the inner code to see the second positional parameter of the main script as its own $1).

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Notes

• sh as the zeroth argument is explained here: What is the second sh in sh -c 'some shell code' sh?

• If in your original script (i.e. without my fix) the shell code you intend to provide to sh -c was double-quoted, then the shell interpreted the script would expand $1 and embed the result in the inner code. Don't do this though.

  # flawed  
  gnome-terminal -- /bin/sh -c "echo 'remember: $1'; exec bash"

  In many cases this would work as you expect; but not in general. In general it is as flawed as embedding {}. Single quoted-code and arguments after it are the right way.

• Single-quoting the code ensures it will get to /bin/sh -c as-is (the inner double-quotes don't matter). Then sh will see the code as

  echo "remember: $1"; exec bash
  

  and it's very good you double-quoted $1 here.