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@dbr cmd 2>&1 >>file does not redirect stderr to the file, but cmd >> file 2>&1 does. Order matters. In the first case, stderr is redirected to the stdout of the shell (possibly a tty if the command is entered interactively), and then stdout is directed to the file.
The left side of 2>&1 tells you what will be redirected, and the right side tells you where to. The & is used on the right side to distinguish stdout (1) or stderr (2) from files named 1 or 2. So, 2>1 would end up creating a new file (if it doesn't exist already) named 1 and dump the stderr result in there. /dev/null
Learn how to use 2>&1 to redirect stderr to stdout and combine error messages with normal output. See examples of debugging scripts, capturing error messages, saving output to a file, and combining output from multiple commands.
Bash's man page mentions there's two ways to redirect stderr and stdout: &> file and >& file.Now, notice that it says both stderr and stdout. In case of this >file 2>&1 we are doing redirection of stdout (1) to file, but then also telling stderr(2) to be redirected to the same place as stdout ! So the purpose may be the same, but the idea slightly different.
2 refers to the second file descriptor of the process, i.e. stderr. > means redirection. &1 means the target of the redirection should be the same location as the first file descriptor, i.e. stdout. So > /dev/null 2>&1 first redirects stdout to /dev/null and then redirects stderr there as well.
Learn how to use 2>&1 and other file descriptors to redirect stdout and stderr in UNIX shell scripting. See examples, explanations and resources for further study.
Understanding the basics of 2>&1 is essential for anyone working with Bash scripts and commands. bash stderr stdout. Share. Facebook Twitter Pinterest LinkedIn Tumblr Email WhatsApp. Related Posts. How To Install and Configure Jenkins on Ubuntu 24.04. How to Install Libreoffice on Ubuntu.
The reason for 2>&1 | tee is to be able to capture both stdout and stderr to a log file and to see it on the screen at the same time. This could be done as >output.txt 2>&1 & tail -f as well, but you wouldn't know when the backgrounded command terminated - is the program terminated or is it running with no output.
Understanding Shell Script's idiom: 2>&1 10 Nov 2015. When we are working with a programming or scripting language, we are constantly using some idioms, some things that are done in this certain way, the common solution to a problem.With Shell Script this is not different, and a quite common idiom, but not so well understood, is the 2>&1, like in ls foo > /dev/null 2>&1.
Resources Aops Wiki Proof that 2=1 Page. Article Discussion View source History. Toolbox. Recent changes Random page Help What links here Special pages. Search. Proof that 2=1. Contents. 1 Proof; 2 Error; 3 Note: 4 Alternate Proof; 5 Error; Proof. 1) . Given. 2) . Multiply both sides by a. 3) . Subtract from both sides. 4) . Factor both sides.