STDOUT输出获取写入到自定义的文件描述符 [英] STDOUT output getting written to custom file descriptor

问题描述

我有一个打开的文件描述符于fd 3，它重定向到一个文件中的函数。我的问题是，从其他功能stdout是越来越写入到FD3被写入文件。因此，code是类似下面。

我不明白，在start_report功能开放文件描述符3如何允许从日志或写入到STDOUT被写入到/tmp/testfile.log任何其他功能输出。奇怪的是，并非所有的标准输出获取写入于fd 3，只有一些。

  start_report（）{
EXEC 3＆GT; /tmp/testfile.log猫＆LT;＆LT;＆EOF GT;及3
一些文本被写入报告。
EOF
}report_update（）{
猫＆LT;＆LT;＆EOF GT;及3
一些文字被写入报告。
EOF
}end_report（）{
猫＆LT;＆LT;＆EOF GT;及3
一些文本结束写入报告。
EOF
EXEC 3＆GT;＆安培;  - 
}日志（）{
＃$ 1 =函数名
＃$ 2 =日志消息
回声$ 1$ 2
}主（）{
start_report
登录$ {FUNCNAME [0]}启动主
update_report
登录$ {FUNCNAME [0]}更新报告
end_report
}主要
 

解决方案

语句

  EXEC 3＆GT; /tmp/testfile.log
 

打开 /tmp/testfile.log 文件描述符3在执行该语句的外壳。即使它出现在函数内部，它会影响执行该功能的外壳;即，它不作用域功能的主体。一旦 start_report 是由当前的shell执行，文件描述符3保持连接到 /tmp/testfile.log 直到关闭或重新分配。

日志，但是，不写文件描述符3;它只写到标准输出（文件描述符1）。其他功能调整其命令的标准输出文件描述符3。

I have a function that opens a file descriptor to fd 3 which redirects to a file. The issue I have is that STDOUT from other functions is getting written to the file that fd3 is writing to. So the code is something like below.

I don't understand how opening file descriptor 3 at start_report function allows output from log or any other function that writes to STDOUT to be written to /tmp/testfile.log. The odd thing is that not all STDOUT is getting written to fd 3, only some.

start_report () {
exec 3>/tmp/testfile.log

cat <<EOF >&3
Some text is written to a report.
EOF
}

report_update () {
cat <<EOF >&3
some more text is written to a report.
EOF
}

end_report () {
cat <<EOF >&3
some ending text is written to a report.
EOF
exec 3>&-
}

log () {
#$1 = function name
#$2 = log message
echo "$1" "$2"
}

main () {
start_report
log "${FUNCNAME[0]}" "Starting main"
update_report
log "${FUNCNAME[0]}" "updating report"
end_report
}

main

解决方案

The statement

exec 3> /tmp/testfile.log

opens /tmp/testfile.log on file descriptor 3 in the shell that executes the statement. Even though it occurs inside a function, it affects the shell that executes the function; i.e., it is not scoped to the body of the function. Once start_report is executed by the current shell, file descriptor 3 remains attached to /tmp/testfile.log until it is closed or reassigned.

log, however, doesn't write to file descriptor 3; it only writes to standard output (file descriptor 1). The other functions redirect the standard output of their commands to file descriptor 3.

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