feature request: shell commands about gomacro HOT 5 OPEN

Both :!ls -la and \!ls -la are feasible, but I think we can do better:

Special commands take a whole line, and can only used at top level, so exchanging data between a special command and Go must be implemented manually by the special command.

If instead I implement an expression that invokes the shell and returns its output (and error),
it can be used anywhere - inside functions, as for condition, etc.

What do you think about something like:

// plain shell syntax, prefix is $
$ls -al

to run a shell command and collect its output as []string, surround it with $()

for i, name := range $(ls -al) {
    println(name)
}

to pass Go expressions (variables, function/method calls...) to shell command, surround them with {} like ipython does:

dir := "/usr/bin"
for i, name := range $(ls -al {dir}) {
    println(name)
}

standard error would be available as second return value:

out, err := $(some_command)

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It would be useful - I am just wondering whether it's slightly out of scope or not...

If implemented, we will have to choose a different special char for shell commands:
! is negation in go, and can already appear at line start - for example !foo() && !bar().

Maybe $ ?

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: is used as a prefix to indicate interpreter commands, so how about :!ls -la (! is used for shell in many programs)?

As for being out of scope, I think it's a pretty common REPL feature.

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Mysql repl uses mysql> \! ls -la, psql uses the same syntax.

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Using ,? If the first char of an input is , the line is treated as shell.

I believe , cannot be a valid char to start an expression. Also , (and .) is right below finger tip and there is no need for shift key. Dot (.) would be nice but it can be the first char of a valid expression (.6 as floating point).

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