{"id":8810,"date":"2022-03-25T11:34:33","date_gmt":"2022-03-25T16:34:33","guid":{"rendered":"https:\/\/www.rushworth.us\/lisa\/?p=8810"},"modified":"2022-03-25T11:40:57","modified_gmt":"2022-03-25T16:40:57","slug":"2-dev-null","status":"publish","type":"post","link":"https:\/\/www.rushworth.us\/lisa\/?p=8810","title":{"rendered":"2>\/dev\/null"},"content":{"rendered":"

A few times now, I’ve encountered individuals with cron jobs or bash scripts where a command execution ends in 2>\/dev\/null<\/tt> … and the individual is stymied by the fact it’s not working but there’s no clue as to why.<\/em> The error output is being sent into a big black hole never to escape!<\/p>\n

The trick here is to understand file descriptors — 1 is basically a shortcut name for STDOUT and 2 is basically a shortcut name for STDERR (0 is STDIN, although that’s not particularly relevant here).\u00a0 So 2>\/dev\/null<\/tt> says “take all of the STDERR stuff and redirect it to \/dev\/null”.<\/p>\n

Sometimes you’ll see bot<\/em>h<\/em> STDERR and STDOUT being redirected either to a file or to \/dev\/null — in that case you will see 2>&1 where the ampersand prior to the “1” indicates the stream is being redirected to a file descriptor (2>1<\/tt> would direct STDOUT to a file named “1”) — so >\/dev\/null 2>&1<\/tt> is the normal way you’d see it written. Functionally, >\/dev\/null 1>&2<\/tt> would be the same thing … but redirecting all output<\/em> into error<\/em> is, conceptually, a little odd.<\/p>\n

To visualize all of this, use a command that will output something to both STDERR and STDOUT — for clarify, I’ve used “1>\/dev\/null” (redirect STDOUT to \/devnull) in conjunction with 2>&1 (redirect STDERR to STDOUT). As written in the text above, the number 1 is generally omitted and just >\/dev\/null<\/tt> is written.<\/p>\n

\u00a0\"\"<\/a><\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

A few times now, I’ve encountered individuals with cron jobs or bash scripts where a command execution ends in 2>\/dev\/null … and the individual is stymied by the fact it’s not working but there’s no clue as to why. The error output is being sent into a big black hole never to escape! The trick …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[33,30],"tags":[632,671,294,633,634],"class_list":["post-8810","post","type-post","status-publish","format-standard","hentry","category-coding","category-system-administration","tag-bash","tag-bash-script","tag-linux","tag-script","tag-shell-script"],"_links":{"self":[{"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/posts\/8810","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8810"}],"version-history":[{"count":4,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/posts\/8810\/revisions"}],"predecessor-version":[{"id":8816,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=\/wp\/v2\/posts\/8810\/revisions\/8816"}],"wp:attachment":[{"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8810"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8810"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rushworth.us\/lisa\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8810"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}