What does " 2>&1 " mean?
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What does " 2>&1 " mean?
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Re: What does " 2>&1 " mean?
#2Not sure why this link and/or question is here, except to say LLMs like this incantation.
It redirects STDERR (2) to where STDOUT is piped already (&1). Good for dealing with random CLI tools if you're not a human.
Re: What does " 2>&1 " mean?
#3Better: Understanding Linux's File Descriptors: A Deep Dive Into '2>&1' and Redirection https://news.ycombinator.com/item?id=41384919 https://news.ycombinator.com/item?id=39095755
Re: What does " 2>&1 " mean?
#4I find it easier to understand in terms of the Unix syscall API. `2>&1` literally translates as `dup2(1, 2)`, and indeed that's exactly how it works. In the classic unix shells that's all that happens; in more modern shells there may be some additional internal bookkeeping to remember state. Understanding it as dup2 means it's easier to understand how successive redirections work, though you also have to know that redirection operators are executed left-to-right, and traditionally each operator was executed immediately as it was parsed, left-to-right. The pipe operator works similarly, though it's a combination of fork and dup'ing, with the command being forked off from the shell as a child before processing the remainder of the line.
Though, understanding it this way makes the direction of the angled bracket a little odd; at least for me it's more natural to understand dup2(2, 1) as 2<1, as in make fd 2 a duplicate of fd 1, but in terms of abstract I/O semantics that would be misleading.
Re: What does " 2>&1 " mean?
#5Not sure why this link and/or question is here, except to say LLMs like this incantation. It redirects STDERR (2) to where STDOUT is piped already (&1). Good for dealing with random CLI tools if you're not a human.
I found the explanation useful, about "why" it is that way. I didn't realize the & before the 1 means to tell it is the filedescriptor 1 and not a file named 1.
Re: What does " 2>&1 " mean?
#6Not sure why this link and/or question is here, except to say LLMs like this incantation. It redirects STDERR (2) to where STDOUT is piped already (&1). Good for dealing with random CLI tools if you're not a human.
I found the explanation useful, about "why" it is that way. I didn't realize the & before the 1 means to tell it is the filedescriptor 1 and not a file named 1.
I get the ocassional file named `1` lying around.
Re: What does " 2>&1 " mean?
#7back when stackoverflow was still good and useful, I asked about some stderr manipulation[0] and learnt a lot from the replies
[0] https://stackoverflow.com/questions/3618078/pipe-only-stderr...
Re: What does " 2>&1 " mean?
#8I always wondered if there ever was a standard stream for stdlog which seems useful, and comes up in various places but usually just as an alias to stderr
Re: What does " 2>&1 " mean?
#9I find it easier to understand in terms of the Unix syscall API. `2>&1` literally translates as `dup2(1, 2)`, and indeed that's exactly how it works. In the classic unix shells that's all that happens; in more modern shells there may be some additional internal bookkeeping to remember state. Understanding it as dup2 means it's easier to understand how successive redirections work, though you also have to know that re…
Yep, there's a strong unifying feel between the Unix api, C, the shell, and also say Perl.
Which is lost when using more modern or languages foreign to Unix.
Re: What does " 2>&1 " mean?
#10I've almost never needed any of these, but there's all sorts of weird redirections you can do in GNU Bash: https://www.gnu.org/software/bash/manual/bash.html#Redirecti...