Question

我找到了以下bash脚本以监控cp进度。

#!/bin/sh
cp_p()
{
   strace -q -ewrite cp -- "${1}" "${2}" 2>&1 \
      | awk '{
        count += $NF
            if (count % 10 == 0) {
               percent = count / total_size * 100
               printf "%3d%% [", percent
               for (i=0;i<=percent;i++)
                  printf "="
               printf ">"
               for (i=percent;i<100;i++)
                  printf " "
               printf "]\r"
            }
         }
         END { print "" }' total_size=$(stat -c '%s' "${1}") count=0
}

我不理解strace命令的“-ewrite”选项。我发现最接近的是strace的手册页

-e write = set执行所有的完整十六进制和ASCII转储写入文件描述符的数据列在指定的集合中。对于例如，查看所有输出活动文件描述符3和5使用-e 写= 3,5。请注意，这是独立于正常的追踪 write（2）系统调用是哪个由选项-e控制跟踪=写。

但是我不明白-ewrite选项的作用。

Answer 1

-ewrite意味着只跟踪“写入”系统调用。

-e expr一个限定表达式，用于修改哪些事件跟踪或如何跟踪它们。格式表达式是：

                     [qualifier=][!]value1[,value2]...

          where qualifier is one of trace,  abbrev,  verbose,
          raw,  signal,  read, or write and value is a quali-
          fier-dependent symbol or number.  The default qual-
          ifier  is trace.  Using an exclamation mark negates
          the set of values.  For example, -eopen means  lit-
          erally -e trace=open which in turn means trace only
          the open system call.  By  contrast,  -etrace=!open
          means  to  trace every system call except open.  In
          addition, the special values all and none have  the
          obvious meanings.

          Note that some shells use the exclamation point for
          history expansion even inside quoted arguments.  If
          so,  you  must  escape the exclamation point with a
          backslash.

Unix strace命令

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