# How to know if $stderr is reopened to /dev/null **URL:** \ **Category:** Ruby\ **Created:** [January 16, 2010, 12:30am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683 "2010-01-16T00:30:39Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:30am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/1 "2010-01-16T00:30:39Z")
Hi, how could I know if $stderr has been redirected to /dev/null? This is, imagine a program does: $stderr.reopen “/dev/null” And later I want to check if it’s redirected to /dev/null or not. I’ve found a method which could work: irb $stderr.inspect “#IO:/dev/null” So I could parse the resulting string. However it doesn’t seem a very “cool” approach. Is there any there any other more ellegant way? Thanks a lot. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:42am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/2 "2010-01-16T00:42:21Z")
Iñaki Baz C. wrote: > “#IO:/dev/null” > > So I could parse the resulting string. However it doesn’t seem a very “cool” > approach. Is there any there any other more ellegant way? > > Thanks a lot. You can use $stderr.tty? if you just need to know if a terminal is listening. -Justin ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:45am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/3 "2010-01-16T00:45:52Z")
El Sábado, 16 de Enero de 2010, Justin C. escribió: > > irb $stderr.inspect > > “#IO:/dev/null” > > > > So I could parse the resulting string. However it doesn’t seem a very > > “cool” approach. Is there any there any other more ellegant way? > > > > Thanks a lot. > > You can use $stderr.tty? if you just need to know if a terminal is > listening. Great! It also works in case $stderr is redirected to a file in which case $stderr.tty? also returns false 🙂 Thanks. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:50am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/4 "2010-01-16T00:50:33Z")
El Sábado, 16 de Enero de 2010, Steven P. escribió:\> \> Hi, how could I know if $stderr has been redirected to /dev/null? > On anything sufficiently Unix-like, you could fstat the filehandle and stat > the path (/dev/null) and check the major and minor device numbers. Thanks. However $stderr.tty? seems simpler for my requeriments 🙂 ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:47am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/5 "2010-01-16T00:47:37Z")
> Hi, how could I know if $stderr has been redirected to /dev/null? On anything sufficiently Unix-like, you could fstat the filehandle and stat the path (/dev/null) and check the major and minor device numbers. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 12:58am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/6 "2010-01-16T00:58:45Z")
On 2010-01-15, Iñaki Baz C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Hi, how could I know if $stderr has been redirected to /dev/null? You couldn’t. Consider a wrapper: exec 5\>/dev/null ruby foo.rb 2\>&5 Or for that matter, a file “/home/ibc/nulldev” which happens to be a character special device using the same driver as /dev/null. … Note that this assumes that what you care about is “$stderr is being thrown away”, not the exact path by which it’s being done. -s ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 1:02am UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/7 "2010-01-16T01:02:15Z")
El Sábado, 16 de Enero de 2010, Seebs escribió:\> Or for that matter, a file “/home/ibc/nulldev” which happens to be > a character special device using the same driver as /dev/null. > > … Note that this assumes that what you care about is “$stderr is > being thrown away”, not the exact path by which it’s being done. Thanks for the clarification. However it’s enough for me using $stderr.tty?. This is, I just care when $stederr is not pointing to a terminal. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [January 16, 2010, 5:50pm UTC](https://www.ruby-forum.com/t/how-to-know-if-stderr-is-reopened-to-dev-null/181683/8 "2010-01-16T17:50:35Z")
On 01/16/2010 01:01 AM, Iñaki Baz C. wrote: > > a character special device using the same driver as /dev/null. > > > > … Note that this assumes that what you care about is “$stderr is > > being thrown away”, not the exact path by which it’s being done. > > Thanks for the clarification. However it’s enough for me using $stderr.tty?. > This is, I just care when $stederr is not pointing to a terminal. Note though, that this also includes cases where stderr is redirected to a pipe. robert@fussel:~$ ruby19 -e ‘p $stderr.tty?’ true robert@fussel:~$ ruby19 -e ‘p $stderr.tty?’ 2\>&1 | cat false robert@fussel:~$ Kind regards robert