python - Pexpect inserts '/r/n' into sendline()

Question

I am using pexpect to automate running a C program in a zsh terminal on Ubuntu 20.04. The program in question is a spectrum convertor: http://www.np.ph.bham.ac.uk/research_resources/programs/spec_conv/spec_conv.c

I have this installed and in my path. I can not run 'spec_conv' in my terminal and the program runs correctly.

When the program starts there is an initial set of options (0-9). I need to choose 5. The second option I click 'Y'. The program then asks for a file name. I have a file called 'file_list' which I type into the terminal and the spectrum is processed as expected.

I am trying to automate this with python. My code so far is:

import pexpect
child = pexpect.spawn('spec_conv')
child.sendline('5')
child.sendline('y')
child.sendline('file_list')
print(child.read())

The code seems to fail at reading the file. The output of print(child.read()) is:

b'
      *****Welcome to SPEC_CONV*****
This program converts spectra between RadWare, Ascii,
Xtrack (GASPWARE) and Ortec (binary Chn & ASCII Spe) formats,
including multiple-spectra (<999) Xtrack files, e.g. from AGATA.
and can gainmatch spectra.
(Ascii means (y) or (x y) data starting from channel zero)
Comment lines starting with # are ignored at the front of
ascii spectra. The 1 or 2 col. format is auto-detected.

 1) to convert RadWare (.spe) ==> Ascii (.txt)
 2) to convert Ascii (.txt) ==> RadWare (.spe)
 3) to convert Ascii (.txt) ==> Xtrack (.spec)
 4) to convert Maestro_Chn (.Chn) ==> Ascii (.txt)
 5) to convert Maestro_Chn (.Chn) ==> RadWare (.spe)
 6) to convert Xtrack (.spec) ==> Ascii (.txt)
 7) to convert Xtrack (.spec) ==> RadWare (.spe)
 8) to convert GENIE (.IEC) ==> RadWare (.spe)
 9) to convert Maestro_Spe (.Spe) ==> RadWare (.spe)
 a) to convert Maestro_Spe (.Spe) ==> Ascii (.txt)
 g) to gainmatch a RadWare spectrum
 0) Quit
5^J
Read spectrum names from list file (y/n) 
y^J
Type filename containing list of spectrum file names:
Cannot open file:  
file_list
'

As you can see at the very end of this extract it is reading the file name as ' file_list ' so cannot find the file. I have tried a couple of solutions proposed in other similar questions and these have not worked:

https://github.com/pexpect/pexpect/issues/238 Preventing linewrap when using pexpect / bash

Adding setwinsize:

import pexpect
child = pexpect.spawn('spec_conv')
child.setwinsize(1000,1000)
child.sendline('5')
child.sendline('y')
child.sendline('file_list')
print(child.read())

The output is the same.

I have also tried changing my .spawn() input by adding '--noediting' as suggested:

import pexpect
child = pexpect.spawn('spec_conv --noediting')
child.setwinsize(1000,1000)
child.sendline('5')
child.sendline('y')
child.sendline('file_list')
print(child.read())

This gives an earlier failed output I don't fully understand the cause of:

b'
       *****Welcome to SPEC_CONV*****
This program converts spectra between RadWare, Ascii,
Xtrack (GASPWARE) and Ortec (binary Chn & ASCII Spe) formats,
including multiple-spectra (<999) Xtrack files, e.g. from AGATA.
and can gainmatch spectra.
(Ascii means (y) or (x y) data starting from channel zero)
Comment lines starting with # are ignored at the front of
ascii spectra. The 1 or 2 col. format is auto-detected.


Unrecognised arguments...usage: spec_conv
 or: spec_conv SpectrumFileName
 ***File --noediting does not exist
5
y
file_list
'

question from:https://stackoverflow.com/questions/65908640/pexpect-inserts-r-n-into-sendline

Answer 1

If you were to run the spawned program manually, you should be able to see that when you reply to the y/n question you only need to type y and the answer is taken immediately without the need for a carriage return.

So you need to send a single character, and not use sendline() which adds a newline to the sent string. Replace

child.sendline('y')

by

child.send('y')