如何將 STDERR output 重定向到變量或 function 以便稍后附加到日志文件？

Question

這就是我嘗試僅將 STDERR output從apt重定向到日志文件的方式，同時使用兩次 function log_trace()在終端上可以看到apt進度報告：

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

問題是因為每個 output 行在循環中處理了兩次，我從log_trace() （實際上來自另一個 function __logger_core ）得到了自定義行前綴» (APT)也打印了兩次：

  » (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  

這是 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
}

我怎樣才能實現這樣的目標：

  » (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.

謝謝！

Answer 1

經過一些試驗和錯誤后，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

換句話說， apt output，無論它是什么，都不會逃脫我的格式 function log_trace() 。