Operation and Maintenance
Linux Operation and Maintenance
How to Redirect Output in a Linux Shell? (STDOUT & STDERR Explained)
How to Redirect Output in a Linux Shell? (STDOUT & STDERR Explained)
Linux输出重定向可分别控制STDOUT（正常输出）和STDERR（错误输出）：>覆盖写入文件，>>追加；2>捕获错误；&>/dev/null丢弃全部输出；|管道传递输出；&>或>file 2>&1合并重定向。
Redirecting output in Linux lets you control where commands send their results—either to files, other commands, or nowhere at all. The two main streams are STDOUT (standard output, for normal program messages) and STDERR (standard error, for warnings and errors). They’re separate, so you can redirect them independently.
Redirect STDOUT to a file
Use > to send normal output to a file. If the file exists, it gets overwritten. Use >> to append instead.
- ls > file_list.txt — saves the list of files to file_list.txt
- echo "log entry" >> app.log — adds a line to the end of app.log
Redirect STDERR to a file
Errors go to file descriptor 2, so use 2> to capture them. This keeps error messages out of your regular output.
- grep "pattern" missing_file.txt 2> errors.log — writes the “No such file” error to errors.log
- command 2>> errors.log — appends errors to an existing log
Redirect both STDOUT and STDERR together
Two common ways: &> (bash/zsh shorthand) or > file 2>&1 (POSIX-compatible). Both send both streams to the same file.
- find /etc -name "*.conf" &> search_results.txt
- find /etc -name "*.conf" > results.txt 2>&1
Discard output or send it to another command
Send output to /dev/null to quietly drop it. Or use | (pipe) to feed STDOUT into another command’s STDIN.
- ping -c 3 example.com > /dev/null 2>&1 — runs silently
- ps aux | grep nginx — finds nginx processes without showing all running programs
- command 2>&1 | grep "error" — pipes both output and errors to grep
Basically just remember: > is for STDOUT, 2> is for STDERR, and &> or > file 2>&1 handle both. It’s not complex—but mixing them up is how logs get lost or errors go unnoticed.
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