io.popen - how to wait for process to finish in Lua?

Question

I have to use io.popen in Lua to run an executable which takes a command line argument. How to wait for a process to finish in the Lua so that expected output can be captured?

  local command = "C:\Program Files\XYZ.exe /all"

  hOutput = io.popen(command)
  print(string.format(""%s", hOutput))

Suppose the executable is XYZ.exe which needs to be called with command line argument /all.

Once io.popen(command) gets executed, the process will return some string which needs to be printed.

My code snippet:

function capture(cmd, raw)
  local f = assert(io.popen(cmd, 'r'))
  -- wait(10000); 
  local s = assert(f:read('*a')) 
  Print(string.format("String: %s",s )) 
  f:close() 
  if raw then return s end 
  s = string.gsub(s, '^%s+', '') 
  s = string.gsub(s, '%s+$', '') 
  s = string.gsub(s, '[\n\r]+', ' ') 
  return s 
end 
local command = capture("C:\Tester.exe /all")

Your help will be appreciated.

function capture(cmd, raw) local f = assert(io.popen(cmd, 'r')) -- wait(10000); local s = assert(f:read('*a')) Print(string.format("String: %s",s )) f:close() if raw then return s end s = string.gsub(s, '^%s+', '') s = string.gsub(s, '%s+$', '') s = string.gsub(s, '[\n\r]+', ' ') return s end local command = capture("C:\Tester.exe /all") — Chet, Mar 08 '11 at 23:20

score 25 · Accepted Answer · edited Feb 18 '19 at 14:16

25

If you are using standard Lua your code looks a bit odd. I am not completely sure about io.popen semantics regarding timeouts or platform dependencies, but the following works at least on my machine.

local file = assert(io.popen('/bin/ls -la', 'r'))
local output = file:read('*all')
file:close()
print(output) -- > Prints the output of the command.

edited Feb 18 '19 at 14:16

rubo77

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answered Mar 09 '11 at 08:43

ponzao

20,684
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1

can you explain, why you need the `assert` around? – rubo77 Feb 22 '19 at 11:30
@rubo77, I haven't used Lua in a while, but based on a quick test I don't think the `assert` is at all useful in this case as `io.popen` seems to return an object even when there is an error. – ponzao Feb 23 '19 at 19:51

score 3 · Answer 2 · answered Nov 04 '21 at 08:40

3

I ended up with this for capturing relatively big output:

io.stdout:setvbuf 'no' 
local file = assert(io.popen('/bin/ls -la', 'r'))
file:flush()  -- > important to prevent receiving partial output
local output = file:read('*all')
file:close()

answered Nov 04 '21 at 08:40

coderofsalvation

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io.popen - how to wait for process to finish in Lua?

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