我希望能够按需记录程序的输出。例如，将输出记录到终端，但是另一个进程可以随时连接当前的输出。
经典的方法是：
myprogram 2>&1 | tee /tmp/mylog
并按需
tail /tmp/mylog
然而，即使在未使用时，这将创建一个不断增长的日志文件，直到驱动器空间耗尽。因此，我的尝试是：
mkfifo /tmp/mylog
myprogram 2>&1 | tee /tmp/mylog
并且按需执行
cat /tmp/mylog
现在我可以随时读取 /tmp/mylog。但是，任何输出都会阻塞程序，直到 /tmp/mylog 被读取。我希望这个 fifo 可以刷新任何未被读回的输入数据。如何实现？
受到您的问题启发，我编写了一个简单的程序，可让您执行以下操作：
$ myprogram 2>&1 | ftee /tmp/mylog
它类似于tee，但是将stdin克隆到stdout和命名管道（现在必须这样）而不阻塞。这意味着如果您想以这种方式记录日志，可能会丢失日志数据，但我认为在您的情况下可以接受。
诀窍在于阻止SIGPIPE信号并忽略对损坏的fifo进行写入时出现的错误。当然，这个示例可以以各种方式进行优化，但是到目前为止，我想它已经做到了。
/* ftee - clone stdin to stdout and to a named pipe
(c) racic@stackoverflow
WTFPL Licence */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int readfd, writefd;
struct stat status;
char *fifonam;
char buffer[BUFSIZ];
ssize_t bytes;
signal(SIGPIPE, SIG_IGN);
if(2!=argc)
{
printf("Usage:\n someprog 2>&1 | %s FIFO\n FIFO - path to a"
" named pipe, required argument\n", argv[0]);
exit(EXIT_FAILURE);
}
fifonam = argv[1];
readfd = open(fifonam, O_RDONLY | O_NONBLOCK);
if(-1==readfd)
{
perror("ftee: readfd: open()");
exit(EXIT_FAILURE);
}
if(-1==fstat(readfd, &status))
{
perror("ftee: fstat");
close(readfd);
exit(EXIT_FAILURE);
}
if(!S_ISFIFO(status.st_mode))
{
printf("ftee: %s in not a fifo!\n", fifonam);
close(readfd);
exit(EXIT_FAILURE);
}
writefd = open(fifonam, O_WRONLY | O_NONBLOCK);
if(-1==writefd)
{
perror("ftee: writefd: open()");
close(readfd);
exit(EXIT_FAILURE);
}
close(readfd);
while(1)
{
bytes = read(STDIN_FILENO, buffer, sizeof(buffer));
if (bytes < 0 && errno == EINTR)
continue;
if (bytes <= 0)
break;
bytes = write(STDOUT_FILENO, buffer, bytes);
if(-1==bytes)
perror("ftee: writing to stdout");
bytes = write(writefd, buffer, bytes);
if(-1==bytes);//Ignoring the errors
}
close(writefd);
return(0);
}
你可以使用以下标准命令进行编译:
$ gcc ftee.c -o ftee
你可以运行以下命令进行快速验证:
$ ping www.google.com | ftee /tmp/mylog
$ cat /tmp/mylog
此外，请注意 - 这不是多路复用器。一次只能有一个进程执行$ cat /tmp/mylog。
这是一个(非常)古老的帖子，但最近我遇到了类似的问题。实际上，我需要将stdin克隆到stdout，并将其复制到一个非阻塞的管道中。第一个答案中提议的ftee确实有所帮助，但对我的用例来说太不稳定了。这意味着如果我没有及时处理数据，我就会丢失可以处理的数据。
我面临的情况是我有一个进程（some_process），它聚合一些数据并每三秒钟将其结果写入stdout。简化后的设置如下（在实际设置中，我使用的是命名管道）：
some_process | ftee >(onlineAnalysis.pl > results) | gzip > raw_data.gz
现在，raw_data.gz必须被压缩并且必须完整。ftee很好地完成了这项工作。但是我中间使用的管道太慢了，无法抓取刷新出来的数据，但如果它可以获得数据，它足够快地处理所有内容，这已经通过常规的tee进行了测试。然而，如果未命名管道发生任何事情，常规tee会阻塞，而我想随时接入，因此tee不是一个选择。回到主题：当我在中间加入一个缓冲区时，情况就变得更好了，结果为：
some_process | ftee >(mbuffer -m 32M| onlineAnalysis.pl > results) | gzip > raw_data.gz
但是这仍然会丢失我可以处理的数据。因此，我前进并将之前提出的免费版扩展为带缓冲的版本（bftee）。它仍具有所有相同的特性，但在写入失败时使用一个（低效？）内部缓冲区。如果缓冲区已满，则仍会丢失数据，但对于我的情况而言效果很好。像往常一样，还有很大的改进空间，但由于我从这里复制了代码，所以我想将其分享给可能需要它的人。
/* bftee - clone stdin to stdout and to a buffered, non-blocking pipe
(c) racic@stackoverflow
(c) fabraxias@stackoverflow
WTFPL Licence */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <unistd.h>
// the number of sBuffers that are being held at a maximum
#define BUFFER_SIZE 4096
#define BLOCK_SIZE 2048
typedef struct {
char data[BLOCK_SIZE];
int bytes;
} sBuffer;
typedef struct {
sBuffer *data; //array of buffers
int bufferSize; // number of buffer in data
int start; // index of the current start buffer
int end; // index of the current end buffer
int active; // number of active buffer (currently in use)
int maxUse; // maximum number of buffers ever used
int drops; // number of discarded buffer due to overflow
int sWrites; // number of buffer written to stdout
int pWrites; // number of buffers written to pipe
} sQueue;
void InitQueue(sQueue*, int); // initialized the Queue
void PushToQueue(sQueue*, sBuffer*, int); // pushes a buffer into Queue at the end
sBuffer *RetrieveFromQueue(sQueue*); // returns the first entry of the buffer and removes it or NULL is buffer is empty
sBuffer *PeakAtQueue(sQueue*); // returns the first entry of the buffer but does not remove it. Returns NULL on an empty buffer
void ShrinkInQueue(sQueue *queue, int); // shrinks the first entry of the buffer by n-bytes. Buffer is removed if it is empty
void DelFromQueue(sQueue *queue); // removes the first entry of the queue
static void sigUSR1(int); // signal handled for SUGUSR1 - used for stats output to stderr
static void sigINT(int); // signla handler for SIGKILL/SIGTERM - allows for a graceful stop ?
sQueue queue; // Buffer storing the overflow
volatile int quit; // for quiting the main loop
int main(int argc, char *argv[])
{
int readfd, writefd;
struct stat status;
char *fifonam;
sBuffer buffer;
ssize_t bytes;
int bufferSize = BUFFER_SIZE;
signal(SIGPIPE, SIG_IGN);
signal(SIGUSR1, sigUSR1);
signal(SIGTERM, sigINT);
signal(SIGINT, sigINT);
/** Handle commandline args and open the pipe for non blocking writing **/
if(argc < 2 || argc > 3)
{
printf("Usage:\n someprog 2>&1 | %s FIFO [BufferSize]\n"
"FIFO - path to a named pipe, required argument\n"
"BufferSize - temporary Internal buffer size in case write to FIFO fails\n", argv[0]);
exit(EXIT_FAILURE);
}
fifonam = argv[1];
if (argc == 3) {
bufferSize = atoi(argv[2]);
if (bufferSize == 0) bufferSize = BUFFER_SIZE;
}
readfd = open(fifonam, O_RDONLY | O_NONBLOCK);
if(-1==readfd)
{
perror("bftee: readfd: open()");
exit(EXIT_FAILURE);
}
if(-1==fstat(readfd, &status))
{
perror("bftee: fstat");
close(readfd);
exit(EXIT_FAILURE);
}
if(!S_ISFIFO(status.st_mode))
{
printf("bftee: %s in not a fifo!\n", fifonam);
close(readfd);
exit(EXIT_FAILURE);
}
writefd = open(fifonam, O_WRONLY | O_NONBLOCK);
if(-1==writefd)
{
perror("bftee: writefd: open()");
close(readfd);
exit(EXIT_FAILURE);
}
close(readfd);
InitQueue(&queue, bufferSize);
quit = 0;
while(!quit)
{
// read from STDIN
bytes = read(STDIN_FILENO, buffer.data, sizeof(buffer.data));
// if read failed due to interrupt, then retry, otherwise STDIN has closed and we should stop reading
if (bytes < 0 && errno == EINTR) continue;
if (bytes <= 0) break;
// save the number if read bytes in the current buffer to be processed
buffer.bytes = bytes;
// this is a blocking write. As long as buffer is smaller than 4096 Bytes, the write is atomic to a pipe in Linux
// thus, this cannot be interrupted. however, to be save this should handle the error cases of partial or interrupted write none the less.
bytes = write(STDOUT_FILENO, buffer.data, buffer.bytes);
queue.sWrites++;
if(-1==bytes) {
perror("ftee: writing to stdout");
break;
}
sBuffer *tmpBuffer = NULL;
// if the queue is empty (tmpBuffer gets set to NULL) the this does nothing - otherwise it tries to write
// the buffered data to the pipe. This continues until the Buffer is empty or the write fails.
// NOTE: bytes cannot be -1 (that would have failed just before) when the loop is entered.
while ((bytes != -1) && (tmpBuffer = PeakAtQueue(&queue)) != NULL) {
// write the oldest buffer to the pipe
bytes = write(writefd, tmpBuffer->data, tmpBuffer->bytes);
// the written bytes are equal to the buffer size, the write is successful - remove the buffer and continue
if (bytes == tmpBuffer->bytes) {
DelFromQueue(&queue);
queue.pWrites++;
} else if (bytes > 0) {
// on a positive bytes value there was a partial write. we shrink the current buffer
// and handle this as a write failure
ShrinkInQueue(&queue, bytes);
bytes = -1;
}
}
// There are several cases here:
// 1.) The Queue is empty -> bytes is still set from the write to STDOUT. in this case, we try to write the read data directly to the pipe
// 2.) The Queue was not empty but is now -> bytes is set from the last write (which was successful) and is bigger 0. also try to write the data
// 3.) The Queue was not empty and still is not -> there was a write error before (even partial), and bytes is -1. Thus this line is skipped.
if (bytes != -1) bytes = write(writefd, buffer.data, buffer.bytes);
// again, there are several cases what can happen here
// 1.) the write before was successful -> in this case bytes is equal to buffer.bytes and nothing happens
// 2.) the write just before is partial or failed all together - bytes is either -1 or smaller than buffer.bytes -> add the remaining data to the queue
// 3.) the write before did not happen as the buffer flush already had an error. In this case bytes is -1 -> add the remaining data to the queue
if (bytes != buffer.bytes)
PushToQueue(&queue, &buffer, bytes);
else
queue.pWrites++;
}
// once we are done with STDIN, try to flush the buffer to the named pipe
if (queue.active > 0) {
//set output buffer to block - here we wait until we can write everything to the named pipe
// --> this does not seem to work - just in case there is a busy loop that waits for buffer flush aswell.
int saved_flags = fcntl(writefd, F_GETFL);
int new_flags = saved_flags & ~O_NONBLOCK;
int res = fcntl(writefd, F_SETFL, new_flags);
sBuffer *tmpBuffer = NULL;
//TODO: this does not handle partial writes yet
while ((tmpBuffer = PeakAtQueue(&queue)) != NULL) {
int bytes = write(writefd, tmpBuffer->data, tmpBuffer->bytes);
if (bytes != -1) DelFromQueue(&queue);
}
}
close(writefd);
}
/** init a given Queue **/
void InitQueue (sQueue *queue, int bufferSize) {
queue->data = calloc(bufferSize, sizeof(sBuffer));
queue->bufferSize = bufferSize;
queue->start = 0;
queue->end = 0;
queue->active = 0;
queue->maxUse = 0;
queue->drops = 0;
queue->sWrites = 0;
queue->pWrites = 0;
}
/** push a buffer into the Queue**/
void PushToQueue(sQueue *queue, sBuffer *p, int offset)
{
if (offset < 0) offset = 0; // offset cannot be smaller than 0 - if that is the case, we were given an error code. Set it to 0 instead
if (offset == p->bytes) return; // in this case there are 0 bytes to add to the queue. Nothing to write
// this should never happen - offset cannot be bigger than the buffer itself. Panic action
if (offset > p->bytes) {perror("got more bytes to buffer than we read\n"); exit(EXIT_FAILURE);}
// debug output on a partial write. TODO: remove this line
// if (offset > 0 ) fprintf(stderr, "partial write to buffer\n");
// copy the data from the buffer into the queue and remember its size
memcpy(queue->data[queue->end].data, p->data + offset , p->bytes-offset);
queue->data[queue->end].bytes = p->bytes - offset;
// move the buffer forward
queue->end = (queue->end + 1) % queue->bufferSize;
// there is still space in the buffer
if (queue->active < queue->bufferSize)
{
queue->active++;
if (queue->active > queue->maxUse) queue->maxUse = queue->active;
} else {
// Overwriting the oldest. Move start to next-oldest
queue->start = (queue->start + 1) % queue->bufferSize;
queue->drops++;
}
}
/** return the oldest entry in the Queue and remove it or return NULL in case the Queue is empty **/
sBuffer *RetrieveFromQueue(sQueue *queue)
{
if (!queue->active) { return NULL; }
queue->start = (queue->start + 1) % queue->bufferSize;
queue->active--;
return &(queue->data[queue->start]);
}
/** return the oldest entry in the Queue or NULL if the Queue is empty. Does not remove the entry **/
sBuffer *PeakAtQueue(sQueue *queue)
{
if (!queue->active) { return NULL; }
return &(queue->data[queue->start]);
}
/*** Shrinks the oldest entry i the Queue by bytes. Removes the entry if buffer of the oldest entry runs empty*/
void ShrinkInQueue(sQueue *queue, int bytes) {
// cannot remove negative amount of bytes - this is an error case. Ignore it
if (bytes <= 0) return;
// remove the entry if the offset is equal to the buffer size
if (queue->data[queue->start].bytes == bytes) {
DelFromQueue(queue);
return;
};
// this is a partial delete
if (queue->data[queue->start].bytes > bytes) {
//shift the memory by the offset
memmove(queue->data[queue->start].data, queue->data[queue->start].data + bytes, queue->data[queue->start].bytes - bytes);
queue->data[queue->start].bytes = queue->data[queue->start].bytes - bytes;
return;
}
// panic is the are to remove more than we have the buffer
if (queue->data[queue->start].bytes < bytes) {
perror("we wrote more than we had - this should never happen\n");
exit(EXIT_FAILURE);
return;
}
}
/** delete the oldest entry from the queue. Do nothing if the Queue is empty **/
void DelFromQueue(sQueue *queue)
{
if (queue->active > 0) {
queue->start = (queue->start + 1) % queue->bufferSize;
queue->active--;
}
}
/** Stats output on SIGUSR1 **/
static void sigUSR1(int signo) {
fprintf(stderr, "Buffer use: %i (%i/%i), STDOUT: %i PIPE: %i:%i\n", queue.active, queue.maxUse, queue.bufferSize, queue.sWrites, queue.pWrites, queue.drops);
}
/** handle signal for terminating **/
static void sigINT(int signo) {
quit++;
if (quit > 1) exit(EXIT_FAILURE);
}
这个版本增加了一个可选参数，用于指定要缓冲的管道块的数量。我的示例调用现在看起来像这样：
some_process | bftee >(onlineAnalysis.pl > results) 16384 | gzip > raw_data.gz
导致在丢弃发生之前需要缓冲16384个块。这会使用大约32 Mbyte的额外内存，但...谁在意呢？
当然，在实际环境中，我使用命名管道，以便根据需要进行连接和断开连接。它看起来像这样：
mkfifo named_pipe
some_process | bftee named_pipe 16384 | gzip > raw_data.gz &
cat named_pipe | onlineAnalysis.pl > results
此外，该进程对信号的反应如下： SIGUSR1 -> 将计数器打印到 STDERR SIGTERM，SIGINT -> 首先退出主循环并将缓冲区刷新到管道，第二个立即终止程序。
也许这会在将来帮助某些人... 祝好
<>重定向操作符（参见3.6.10 打开文件描述符以供读写）使得使用它打开的文件/管道的写入变为非阻塞的。
这样应该可以工作：$ mkfifo /tmp/mylog
$ exec 4<>/tmp/mylog
$ myprogram 2>&1 | tee >&4
$ cat /tmp/mylog # on demend
在 #bash IRC 频道上，gniourf_gniourf 给出了解决方案。
tail在该fifo上无法工作，可能是因为它等待从未到来的EOF。cat的输出有效，但似乎只提供自上次cat以来的任何输出。因此，我想知道使用了什么缓冲区（通常的管道/ fifo缓冲区？）以及它能持续多长时间，当它被填满时会发生什么。 - dronus可以将日志传输到一个UDP套接字中。由于UDP是无连接的，因此不会阻塞发送程序。当然，如果接收器或网络无法跟上，则会丢失日志。
myprogram 2>&1 | socat - udp-datagram:localhost:3333
socat udp-recv:3333 -
BusyBox通常用于嵌入式设备，可以通过以下方式创建一个RAM缓冲日志：
syslogd -C
可以填写的内容
logger
并且被读取
logread
功能相当不错，但只提供一个全局日志。
$ screen -t sometitle myprogram
Hit Ctrl+A, then d to detach it.
每当您想查看输出时，请重新附加它：
$ screen -DR sometitle
Hit Ctrl-A, then d to detach it again.
# sample code 1
# terminal window 1
rm -f /tmp/mylog
touch /tmp/mylog
while sleep 2; do date '+%Y-%m-%d_%H.%M.%S'; done 2>&1 | while IFS="" read -r line; do
lno=$((lno+1))
#echo $lno
array[${lno}]="${line}"
if [[ $lno -eq 10 ]]; then
lno=$((lno+1))
array[${lno}]="-------------"
printf '%s\n' "${array[@]}" > /tmp/mylog
unset lno array
fi
printf '%s\n' "${line}"
done
# terminal window 2
tail -f /tmp/mylog
#------------------------
# sample code 2
# code taken from:
# https://dev59.com/PlnUa4cB1Zd3GeqPY0Mb
# terminal window 1
# server
(
rm -f /tmp/to /tmp/from
mkfifo /tmp/to /tmp/from
while true; do
while IFS="" read -r -d $'\n' line; do
printf '%s\n' "${line}"
done </tmp/to >/tmp/from &
bgpid=$!
exec 3>/tmp/to
exec 4</tmp/from
trap "kill -TERM $bgpid; exit" 0 1 2 3 13 15
wait "$bgpid"
echo "restarting..."
done
) &
serverpid=$!
#kill -TERM $serverpid
# client
(
exec 3>/tmp/to;
exec 4</tmp/from;
while IFS="" read -r -d $'\n' <&4 line; do
if [[ "${line:0:1}" == $'\177' ]]; then
printf 'line from stdin: %s\n' "${line:1}" > /dev/null
else
printf 'line from fifo: %s\n' "$line" > /dev/null
fi
done &
trap "kill -TERM $"'!; exit' 1 2 3 13 15
while IFS="" read -r -d $'\n' line; do
# can we make it atomic?
# sleep 0.5
# dd if=/tmp/to iflag=nonblock of=/dev/null # flush fifo
printf '\177%s\n' "${line}"
done >&3
) &
# kill -TERM $!
# terminal window 2
# tests
echo hello > /tmp/to
yes 1 | nl > /tmp/to
yes 1 | nl | tee /tmp/to
while sleep 2; do date '+%Y-%m-%d_%H.%M.%S'; done 2>&1 | tee -a /tmp/to
# terminal window 3
cat /tmp/to | head -n 10
logrotate。tail --follow=name --retry my.log
这就是你所需要的。你会得到与你的终端一样多的滚动条。
不需要任何非标准的东西。我没有尝试过处理小日志文件，但我们所有的日志都是这样轮换，我从未注意到丢失行。
为了跟随Fabraxias的脚步，我将分享一下我对racic代码的小修改。在我的一个使用场景中，我需要抑制对STDOUT的写入，因此我添加了另一个参数：swallow_stdout。如果它不是 0，那么对STDOUT的输出将被关闭。
由于我不是C编码人员，所以我在阅读代码时添加了注释，或许它们对其他人有用。
/* ftee - clone stdin to stdout and to a named pipe
(c) racic@stackoverflow
WTFPL Licence */
// gcc /tmp/ftee.c -o /usr/local/bin/ftee
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int readfd, writefd; // read & write file descriptors
struct stat status; // read file descriptor status
char *fifonam; // name of the pipe
int swallow_stdout; // 0 = write to STDOUT
char buffer[BUFSIZ]; // read/write buffer
ssize_t bytes; // bytes read/written
signal(SIGPIPE, SIG_IGN);
if(3!=argc)
{
printf("Usage:\n someprog 2>&1 | %s [FIFO] [swallow_stdout] \n"
"FIFO - path to a named pipe (created beforehand with mkfifo), required argument\n"
"swallow_stdout - 0 = output to PIPE and STDOUT, 1 = output to PIPE only, required argument\n", argv[0]);
exit(EXIT_FAILURE);
}
fifonam = argv[1];
swallow_stdout = atoi(argv[2]);
readfd = open(fifonam, O_RDONLY | O_NONBLOCK); // open read file descriptor in non-blocking mode
if(-1==readfd) // read descriptor error!
{
perror("ftee: readfd: open()");
exit(EXIT_FAILURE);
}
if(-1==fstat(readfd, &status)) // read descriptor status error! (?)
{
perror("ftee: fstat");
close(readfd);
exit(EXIT_FAILURE);
}
if(!S_ISFIFO(status.st_mode)) // read descriptor is not a FIFO error!
{
printf("ftee: %s in not a fifo!\n", fifonam);
close(readfd);
exit(EXIT_FAILURE);
}
writefd = open(fifonam, O_WRONLY | O_NONBLOCK); // open write file descriptor non-blocking
if(-1==writefd) // write file descriptor error!
{
perror("ftee: writefd: open()");
close(readfd);
exit(EXIT_FAILURE);
}
close(readfd); // reading complete, close read file descriptor
while(1) // infinite loop
{
bytes = read(STDIN_FILENO, buffer, sizeof(buffer)); // read STDIN into buffer
if (bytes < 0 && errno == EINTR)
continue; // skip over errors
if (bytes <= 0)
break; // no more data coming in or uncaught error, let's quit since we can't write anything
if (swallow_stdout == 0)
bytes = write(STDOUT_FILENO, buffer, bytes); // write buffer to STDOUT
if(-1==bytes) // write error!
perror("ftee: writing to stdout");
bytes = write(writefd, buffer, bytes); // write a copy of the buffer to the write file descriptor
if(-1==bytes);// ignore errors
}
close(writefd); // close write file descriptor
return(0); // return exit code 0
}