[Bug 1394136] Re: if statement with pipe to grep randomly fails if pipefail is set

[xhienne]

This is not a bug, although some might disagree with the current
behavior of bash.

With a command like 'yes | grep -q .', because the grep terminates early
and the yes is writing past the end of the pipe buffer, the yes process
is _always_ terminated with a SIGPIPE signal (which translates to a
return value of 141). Combined with the pipefail option, the whole
command is considered to have failed.

pipefail should be used scarcely, that's why it is not enabled by
default.

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to bash in Ubuntu.
https://bugs.launchpad.net/bugs/1394136

Title:
  if statement with pipe to grep randomly fails if pipefail is set

Status in bash package in Ubuntu:
  Confirmed

Bug description:
  The following bash script will fail randomly on trusty but when tested
  on saucy it worked all the time. On the system we test we have kvm
  installed and the if statement should evaluate to false and we should
  see ten PASS lines and no Error. And this should happen all the time.

  ======
  #!/bin/bash 

  set -eu
  set -o pipefail

  if ! lsmod | grep -q -e ^kvm_intel -e ^kvm_amd ; then
      echo 'Error: check that virtualisation is enabled in your BIOS'
  else
      echo "PASS"
  fi
  =======

  As can be seen if I run it 10 times I get 2 PASS and 8 failures

  =======
  kerrin at kerrin-HP-Z620-Workstation:~/ce_build$ for i in $(seq 0 9) ; do bash test-simple.bash ; done
  PASS
  PASS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  Error: check that virtualisation is enabled in your BIOS
  =======

  Now if I turn off the pipefail then the script passes all the time and
  just prints out 10 PASS lines.

  The script uses bash, grep and lsmod and I have the following versions
  on trusty of them

  kerrin at kerrin-HP-Z620-Workstation:~/ce_build$ dpkg -l | grep bash
  ii  bash                                                  4.3-7ubuntu1.5                                      amd64        GNU Bourne Again SHell
  ii  bash-completion                                       1:2.1-4                                             all          programmable completion for the bash shell
  ii  command-not-found                                     0.3ubuntu12                                         all          Suggest installation of packages in interactive bash sessions
  kerrin at kerrin-HP-Z620-Workstation:~/ce_build$ dpkg -l | grep grep
  ii  grep                                                  2.16-1                                              amd64        GNU grep, egrep and fgrep
  kerrin at kerrin-HP-Z620-Workstation:~/ce_build$ dpkg -l | grep kmod
  ii  kmod                                                  15-0ubuntu6                                         amd64        tools for managing Linux kernel modules
  ii  libkmod2:amd64                                        15-0ubuntu6                                         amd64        libkmod shared library
  ii  module-init-tools                                     15-0ubuntu6                                         all          transitional dummy package (module-init-tools to kmod)

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/bash/+bug/1394136/+subscriptions