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shell: Lua module for nonblocking system shell command executions

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-shell

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua5.1-resty-shell

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-shell v0.3 released on Jul 01 2020.

lua-resty-shell - Lua module for nonblocking system shell command executions

Synopsis

local shell = require "resty.shell"

local stdin = "hello"
local timeout = 1000  -- ms
local max_size = 4096  -- byte

local ok, stdout, stderr, reason, status =
    shell.run([[perl -e 'warn "he\n"; print <>']], stdin, timeout, max_size)
if not ok then
    -- ...
end

Functions

run

syntax: ok, stdout, stderr, reason, status = shell.run(cmd, stdin?, timeout?, max_size?)

context: all phases supporting yielding

Runs a shell command, cmd, with an optional stdin.

The cmd argument can either be a single string value (e.g. "echo 'hello, world'") or an array-like Lua table (e.g. {"echo", "hello, world"}). The former is equivalent to {"/bin/sh", "-c", "echo 'hello, world'"}, but simpler and slightly faster.

When the stdin argument is nil or "", the stdin device will immediately be closed.

The timeout argument specifies the timeout threshold (in ms) for stderr/stdout reading timeout, stdin writing timeout, and process waiting timeout.

The max_size argument specifies the maximum size allowed for each output data stream of stdout and stderr. When exceeding the limit, the run() function will immediately stop reading any more data from the stream and return an error string in the reason return value: "failed to read stdout: too much data".

Upon terminating successfully (with a zero exit status), ok will be true, reason will be "exit", and status will hold the sub-process exit status.

Upon terminating abnormally (non-zero exit status), ok will be false, reason will be "exit", and status will hold the sub-process exit status.

Upon exceeding a timeout threshold or any other unexpected error, ok will be nil, and reason will be a string describing the error.

When a timeout threshold is exceeded, the sub-process will be terminated as such:

  1. first, by receiving a SIGTERM signal from this library,
  2. then, after 1ms, by receiving a SIGKILL signal from this library.

Note that child processes of the sub-process (if any) will not be terminated. You may need to terminate these processes yourself.

When the sub-process is terminated by a UNIX signal, the reason return value will be "signal" and the status return value will hold the signal number.

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-shell.