{"id":134,"date":"2010-03-05T20:10:44","date_gmt":"2010-03-05T09:10:44","guid":{"rendered":"http:\/\/chuchuva.com\/pavel\/?p=134"},"modified":"2016-01-12T07:37:54","modified_gmt":"2016-01-11T20:37:54","slug":"how-to-redirect-output-of-console-program-to-a-file-in-powershell","status":"publish","type":"post","link":"https:\/\/chuchuva.com\/pavel\/2010\/03\/how-to-redirect-output-of-console-program-to-a-file-in-powershell\/","title":{"rendered":"How to redirect output of console program to a file in PowerShell"},"content":{"rendered":"

At some stage I decided I need backup plan for my virtual server. After some intensive web surfing I found brilliant command line tool – s3.exe<\/a>. The next step was to schedule to run it periodically, every night, when everybody is sleeping.<\/p>\n

\"Night\"<\/p>\n

I decided to use PowerShell. It’s new, it’s powerful, it comes pre-installed with Windows Server 2008. PowerShell is very popular among system administrators.<\/p>\n

Also, I got an idea to save output of backup application to log file so that I could see results later. And this is where things didn’t work as I expected. Here’s how to redirect console program output to a file:<\/p>\n

s3.exe > log.txt<\/code><\/pre>\n
If you run this you will be surprised to find that log.txt is empty. As it turns out s3.exe, being a good Windows citizen, writes errors to STDERR stream. To redirect error output to the same file you need to add magic string 2>&1:<\/p>\n
s3.exe 2>&1 > log.txt<\/code><\/pre>\n
Two new problems appear. First, errors appear as exceptions in log file:<\/p>\n
s3.exe : s3.exe version 1.6 - check for updates at http:\/\/s3.codeplex.com\r\nAt PS Logging.ps1:4 char:43\r\n+ s3.exe <<<<  2>&1 > log.txt\r\n    + CategoryInfo          : NotSpecified: (s3.exe version ...s3.codeplex.com\r\n   :String) [], RemoteException\r\n    + FullyQualifiedErrorId : NativeCommandError<\/code><\/pre>\n
PowerShell helpfully wraps STDERR output into exceptions<\/a>. This is nice but I don’t need it! All I want is to see how a program worked by examining log file. Do this to unwrap exceptions and show plain text:<\/p>\n
s3.exe 2>&1 | foreach-object {$_.ToString()} | Out-File log.txt<\/code><\/pre>\n
And second, errors are\u00a0out of order with normal output. They could appear before or after normal lines emitted by a program, making it hard to diagnose problem. To confirm that, I created a simple console program:<\/p>\n
static void Main(string[] args)\r\n{\r\n   for (int i = 0; i < 10; i++)\r\n   {\r\n      Console.WriteLine(\"Hello\");\r\n   }\r\n   Console.Error.WriteLine(\"Bah bah\");\r\n   for (int i = 0; i < 10; i++)\r\n   {\r\n      Console.WriteLine(\"2\");\r\n   }\r\n}\r\n<\/code><\/pre>\n
If you run this program from PowerShell and redirect output to a file, error message (bah bah) could appear anywhere in the log file:<\/p>\n
Hello\r\nBah bah<\/strong>\r\nHello\r\nHello\r\nHello\r\nHello\r\nHello\r\nHello\r\nHello\r\nHello\r\nHello\r\n2\r\n2\r\n2\r\n2\r\n2\r\n2\r\n2\r\n2\r\n2\r\n2<\/code><\/pre>\n
The solution I came up with is to let old reliable cmd.exe to do the work:<\/p>\n
cmd \/c s3.exe `>log.txt 2`>`&1<\/code><\/pre>\n
Note backsticks – I use them to prevent PowerShell from parsing redirect operators.<\/p>\n
Links<\/h4>\n
PowerShell ABC’s – O is for Output<\/a>
\nHow to capture exe output to a PowerShell variable<\/a>
\nAnother approach to unwrap exceptions: use add-content cmdlet<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
At some stage I decided I need backup plan for my virtual server. After some intensive web surfing I found brilliant command line tool – s3.exe. The next step was to schedule to run it periodically, every night, when everybody is sleeping. I decided to use PowerShell. It’s new, it’s powerful, it comes pre-installed with … Continue reading How to redirect output of console program to a file in PowerShell<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[7],"tags":[10],"class_list":["post-134","post","type-post","status-publish","format-standard","hentry","category-software","tag-powershell"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/posts\/134","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/comments?post=134"}],"version-history":[{"count":0,"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/posts\/134\/revisions"}],"wp:attachment":[{"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/media?parent=134"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/categories?post=134"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chuchuva.com\/pavel\/wp-json\/wp\/v2\/tags?post=134"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}