This implementation causes one extra process for system to run. MikkoRantalainen I already explained that it spawns a subshell and is less efficient. The point of this approach is that if efficiency isn't a big deal and it rarely is , this way is easier to remember and harder to get wrong.
MikkoRantalainen I've updated my answer with a variant that avoids spawning a subshell. UNIX does not support redirecting to a stream, only to file descriptor pointed by a stream. Redirections from script himself You could plan redirections from the script itself:! Simple and combined logs! Hauri F. Hauri See further: Pipe output to two different commands , then follow link to more detailled answer on this duplicate in comment. The Overflow Blog. Podcast Making Agile work for data science.
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Always give them explicitly in a "static" fashion. This still will not protect you against every exploit, but at least helps to detect and avoid common scripting errors. If you're executing a simple command eg, not a pipe , you could remove these inner braces.
You can't pipe outside the command as piping makes a subshell in bash and zsh , and the assignment to the variable in the subshell wouldn't be available to the current shell. Thanks to this answer for the general idea. Iterating a bit on Tom Hale's answer , I've found it possible to wrap the redirection yoga into a function for easier reuse.
For example:. It's almost certainly possible to simplify this further. Haven't tested especially-thoroughly, but it does appear to work with both bash and ksh. This is an interesting problem to which I hoped there was an elegant solution. Sadly, I end up with a solution similar to Mr. Leffler, but I'll add that you can call useless from inside a Bash function for improved readability:. So you swap stdout and stderr. Using fd 3 as the temporary storage in the standard swap algorithm. If you want to capture AND print use tee to make a duplicate.
NOTE: That is an awful lot of redirections in a single line and the order matters. The OP said he still wanted to use not just print stdout, like. I recommend moving it into a function or file also-useless. I think you want to capture stderr , stdout and exitcode if that is your intention you can use this code:.
This scripts capture the stderr , stdout as well as the exitcode. Therefore, the stdout will look like:. Then, we can capture the piped stdout from the stdin of the command group with read. This command reads a line from the file descriptor stdin and split it into fields. Our script uses read -r -d '' , where read -r does not allow backslashes to escape any characters, and -d '' continues until the first character '' is read, rather than newline.
If you want to bypass the use of a temporary file you may be able to use process substitution. I haven't quite gotten it to work yet. This was my first attempt:. So the process substitution is doing generally the right thing Process substitution has bought me the ability to work with a data stream which is no longer in STDERR, unfortunately I don't seem to be able to manipulate it the way that I want. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How to store standard error in a variable Ask Question. Asked 12 years, 7 months ago. Active 1 month ago. Viewed k times. Let's say I have a script like the following: useless. You can also redirect both standard output and standard error to a same file.
In below example, error get printed on terminal and the file. Use below code to redirect standard error and output to same file and also display to terminal. We can also redirect standard input from terminal to a file. Subsequently, programs read from file, instead of terminal. Active 7 years ago. Viewed 6k times. Improve this question.
Aman Aman 2 2 gold badges 8 8 silver badges 18 18 bronze badges. The redirection happens before ls ever starts. It's handled by the shell. Your question asks about standard output and standard error. Why does the title refer to standard input? Barmar, sorry it was a typo, thanks for pointing it out : — Aman.
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