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Nifty UNIX tip of the day

I was writing a quick script and wanted to process the standard error (stderr) output of a program and ignore the standard output (stdout).

My goal was to check a Webserver was successfully serving a page and returning a successfulll HTTP code (Code 200). I was using the wget tool. Wget has a '-S' option for outputting the HTTP headers as a page is loaded, but these are sent to stderr not stdout. Everyone (even my mother) knows you can redirect stdout with '>' or pipe (|) it onto the next program. Most people know that you can redirect stderr to a file using '2>'. But by itsself, that doesn't let you pipe it to the next command in the chain. To do that, you need to redirect the stderr to stdout. In bash, this is done by '2>&1'. The you can pipe onto the next command. eg/

[djg@caperdu]$ wget -S localhost -O /dev/null  2>&1 | grep -c "1 HTTP"
1

wget -S localhost > out 2>&1

Replies: 1 Comment

You can also try "wget -o /dev/stdout -O /dev/stdout
http://www.corunet.com"; without the need of pipes. It works flawlesly.
I found it while aplying your advice and, for me, is even more
comfortable.

David Pardo said @ 12/28/2004 01:39 PM EST