Strange pexpect behaviour: just duplicates stdin

Nikolaus Rath Nikolaus at rath.org
Tue Mar 31 03:23:40 CEST 2009


Hello,

I have a strange problem with pexpect:

$ cat test.py
#!/usr/bin/python

import pexpect

child = pexpect.spawn("./test.pl")

while True:
    try:
        line = raw_input()
    except EOFError:
        break

    child.sendline(line)
    print child.readline().rstrip("\r\n")

child.close()

$ cat test.pl
#!/usr/bin/perl
# Replace all digits by __
while (<>) {
    s/[0-9]+/__/g;
    print;
}

$ echo bla24fasel | ./test.pl
bla__fasel

$ echo bla24fasel | ./test.py
bla24fasel


Why doesn't the last command return bla__fasel too?


I extracted this example from an even stranger problem in a bigger
program. In there, pexpect sometimes returns both the string send with
sendline() *and* the output of the child program, sometimes the
correct output of the child, and sometimes only the input it has send
to the child. I couldn't figure out a pattern, but the above example
always produces the same result.


Anyone able to help?


Best,

   -Nikolaus

-- 
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