No output from awk only when redirected to pipe or file [duplicate]

问题

This question already has an answer here:

awk not printing to file (1 answer)

Closed 12 months ago.

I have a rather simple script (print content from a tty after adding timestamp to every row). It outputs nicely on the command line, but redirecting the output with > does not work. Why not?

Here is the script:

#!/bin/bash
awk '{ print strftime("%Y-%m-%d %H:%M:%S |"), $0; }' "$1"

Running it as is, like timecat /dev/ttyACM0 works fine, I see the content in my terminal.

But if I run timecat /dev/ttyACM0 > ~/tmp.log, nothing comes out. Same with tee. The file is there, but it is empty.

Is there something weird with awk in the script, how can I modify this to make the redirection work?

回答1:

All this needed was to flush the print within the command, replacing the last script row with this:

awk '{ print strftime("%Y-%m-%d %H:%M:%S |"), $0; fflush(); }' $tty
                                                  ^^^^^^^^^

来源：https://stackoverflow.com/questions/54450368/no-output-from-awk-only-when-redirected-to-pipe-or-file