如何将 STDERR output 重定向到变量或 function 以便稍后附加到日志文件？

Question

这就是我尝试仅将 STDERR output从apt重定向到日志文件的方式，同时使用两次 function log_trace()在终端上可以看到apt进度报告：

apt update 2> >(log_trace "(APT)") | while read -r line; do
    if [[ $line != "All packages are up to date." ]]; then
        bool_update_required=1
    fi
    log_trace "(APT)" <<<"$line"
done

问题是因为每个 output 行在循环中处理了两次，我从log_trace() （实际上来自另一个 function __logger_core ）得到了自定义行前缀» (APT)也打印了两次：

  » (APT)   » (APT)   
  » (APT)   » (APT) WARNING: apt does not have a stable CLI interface. Use with caution in scripts.  
  » (APT)   » (APT)   
  » (APT) Reading package lists... 
  » (APT)   » (APT) E: Could not get lock /var/lib/apt/lists/lock. It is held by process 1490 (packagekitd)  
  » (APT)   » (APT) E: Unable to lock directory /var/lib/apt/lists/  
  » (APT)   » (APT) E: Problem renaming the file /var/cache/apt/srcpkgcache.bin.J7Fixb to /var/cache/apt/srcpkgcache.bin - rename (2: No such file or directory)  
  » (APT)   » (APT) W: You may want to run apt-get update to correct these problems  
  » (APT)   » (APT) E: The package cache file is corrupted  

这是 function 本身：

log_trace() {
    local line
    # Output automatically written to $_LOG_FILE
    # Arguments: 1
    # ARG -1: printf variable for formatting the log
    while IFS= read -r line; do
        __logger_core "trace" "$(printf "%s %s" "${1:-UNKNOWN}" "$line")"
    done
}

我怎样才能实现这样的目标：

  » (APT) This is just a progress report, no error or warning
  » (APT) You don't see STDERR output because it safely resides in the log file already
  » (APT) All packages are up to date.

谢谢！

Answer 1

经过一些试验和错误后，它的工作原理如下：

while read -r line; do
    if [[ $line == "All packages are up to date." ]]; then
        bool_update_required=0
    fi
    log_trace "(APT)" <<<"$line"
done < <(apt update 2>&1)       # format all `apt` output, incl. errors/warnings

换句话说， apt output，无论它是什么，都不会逃脱我的格式 function log_trace() 。