STDIN inheritance during exec and difference between getc and sysread

ruby-talk
1

Hi all!

I've accidentally found that "getc" and "sysread" behave differently
after "exec"
getc does not get remaining data from the STDIN but sysread does it

bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $ echo -n ab | ruby -e "p STDIN.getc; exec 'ruby',
'-e', 'p STDIN.getc'"
"a"
nil
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $ echo -n ab | ruby -e "p STDIN.sysread(1); exec
'ruby', '-e', 'p STDIN.sysread(1)'"
"a"
"b"
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $

why so? where is "b" in the first case?

···

--
Posted via http://www.ruby-forum.com/.

2

getc uses Ruby I/O buffering in user space, so the process read
more bytes than it needed the first time getc was called.

Buffered I/O leads to surprises like this behavior across fork/exec.

···

Dmitry Bolshakov <lists@ruby-forum.com> wrote:

Hi all!

I've accidentally found that "getc" and "sysread" behave differently
after "exec"
getc does not get remaining data from the STDIN but sysread does it

bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $ echo -n ab | ruby -e "p STDIN.getc; exec 'ruby',
'-e', 'p STDIN.getc'"
"a"
nil
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $ echo -n ab | ruby -e "p STDIN.sysread(1); exec
'ruby', '-e', 'p STDIN.sysread(1)'"
"a"
"b"
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $
bdimych@mint-vbox ~ $

why so? where is "b" in the first case?