Skip to main content

interoperability - How to trigger UNIX command-line command from Mathematica notebook?


At UNIX command line, one can run ls -la $HOME. How to trigger this from Mathematica notebooks?


Run["!ls -la $HOME"]



32512

Returns some integer -- what is it? -- but not the normal output.



Answer



The Run command returns the exit code of the program being run. In your case, the program is "!ls" which probably doesn't exist on your system (If you try


sh -c '!ls -la $HOME'

you'll also get an error). Why it returns 32512 instead of 127 (which is the return value I get by the shell) I don't know; however I notice that 32512=127â‹…256, so I guess it's in order to better distinguish valid exit codes (usually telling about errors during the execution) from errors occurring when trying to execute the command (like not finding the executable).


If you start a raw kernel and type



Run["ls -la $HOME"]

(without exclamation mark) you'll see the output of the ls command on standard output, and a returned value of 0 (the exit code of ls). If you do it from a notebook, the standard out will be the one Mathematica was started with; if started from a terminal, that's where the output will happen, otherwise it will end up elsewhere or even nowhere (in my test, the directory listing ended up in .xsession-errors because I started Mathematica through the desktop environment).


If you are interested in the actual output, you have to use a file reading command, and use the special "!" syntax; for example Import as suggested by user18792,


Import["!ls -la $HOME", "Text"]

giving you all the output in a single string, or ReadList as suggested by Gustavo Delfino,


ReadList["!ls -la",String]

giving you a list of strings, each containing a single line of the output.



Note that the exclamation mark says you want to get the output of a command instead of the contents of a file (whose name would have gone at that point otherwise). That's why you don't put the exclamation mark at the Run command: Its argument is not a file to read, but already a command to execute, thus you don't need (and cannot use) the exclamation mark "escape" to use a command instead of a file.


If you need both the output and the exit code, apparently in version 10 you can use RunProcess (I can't check that because I don't have access to v10). From the documentation, I get that the command would look like the following:


RunProcess[{"ls", "-la", Environment["HOME"]}]

Comments

Post a Comment

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...
Post a Comment
Read more

plotting - Plot 4D data with color as 4th dimension

I have a list of 4D data (x position, y position, amplitude, wavelength). I want to plot x, y, and amplitude on a 3D plot and have the color of the points correspond to the wavelength. I have seen many examples using functions to define color but my wavelength cannot be expressed by an analytic function. Is there a simple way to do this? Answer Here a another possible way to visualize 4D data: data = Flatten[Table[{x, y, x^2 + y^2, Sin[x - y]}, {x, -Pi, Pi,Pi/10}, {y,-Pi,Pi, Pi/10}], 1]; You can use the function Point along with VertexColors . Now the points are places using the first three elements and the color is determined by the fourth. In this case I used Hue, but you can use whatever you prefer. Graphics3D[ Point[data[[All, 1 ;; 3]], VertexColors -> Hue /@ data[[All, 4]]], Axes -> True, BoxRatios -> {1, 1, 1/GoldenRatio}]
Post a Comment
Read more