How to pass a parameter to a shell script in nginx lua

Question

I'm doing a simple test to see if I can run a shell script in nginx easily. Lua seems a good solution. So I added

content_by_lua_block {
   local myvar = "abcd"
   local file = io.popen("myshellscript.sh myvar")
   local result = file:read("*a")
   ngx.say(result)
}

in my nginx.conf. In myshellscript.sh, I use echo "#1" to print the value of the parameter. But instead of seeing "abcd", I see "myvar" from the output. So what's the proper way to pass a variable as a parameter to the shell script in nginx lua? I know os.execute("myshellscript.sh myvar") can do the similar job as popen, but I don't know how to get the output to the stdout or the exit code from the shell script.

Luatic · Answer 1 · 2022-08-12T08:50:03.987

0

You need to substitute myvar with the value of your variable - otherwise you're passing the literal string myvar. Since abcd does not need to be quoted, simply concatenating myvar will work for this example:

local file = io.popen("myshellscript.sh " .. myvar)

or for a more robust solution that quotes strings using single quotes:

local function quote(param)
    return "'" .. param:gsub("'", [['\'']]) .. "'"
end
local file = io.popen("myshellscript.sh " .. quote(myvar))

edited Aug 12 '22 at 08:50

answered Aug 11 '22 at 20:35

Luatic

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You may replace `[['"'"']]` with `[['\'']]` – Egor Skriptunoff Aug 11 '22 at 21:03
@LMD Just tried the simple solution. It worked for me. Thanks! – Wqh Aug 11 '22 at 21:06
@EgorSkriptunoff may I? [Wouldn't this rely on bash?](https://stackoverflow.com/a/16605140/7185318) – Luatic Aug 12 '22 at 06:06
@LMD - The link in your comment is about `$'...'` format, not about `'...'` and `\'`. You can check in dash: `sh -c "echo 'abc'\''def'"` – Egor Skriptunoff Aug 12 '22 at 08:04

How to pass a parameter to a shell script in nginx lua

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