08-04-2009
You could create a named pipe and use that to communicate between the two. Create the file mkfifo pipe_name, with one shell, cat some_file > pipe_name. It will appear to hang, with second shell, cat pipe_name and the output will be displayed and the first shell will complete.
Now with the second shell, cat pipe_name, this will appear to hang. With the first shell, cat some_file > pipe_name. The output will be displayed in the second.
That may seem clear as mud.
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LEARN ABOUT POSIX
systemd-cat
SYSTEMD-CAT(1) systemd-cat SYSTEMD-CAT(1)
NAME
systemd-cat - Connect a pipeline or program's output with the journal
SYNOPSIS
systemd-cat [OPTIONS...] [COMMAND] [ARGUMENTS...]
systemd-cat [OPTIONS...]
DESCRIPTION
systemd-cat may be used to connect the standard input and output of a process to the journal, or as a filter tool in a shell pipeline to
pass the output the previous pipeline element generates to the journal.
If no parameter is passed, systemd-cat will write everything it reads from standard input (stdin) to the journal.
If parameters are passed, they are executed as command line with standard output (stdout) and standard error output (stderr) connected to
the journal, so that all it writes is stored in the journal.
OPTIONS
The following options are understood:
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
-t, --identifier=
Specify a short string that is used to identify the logging tool. If not specified, no identification string is written to the journal.
-p, --priority=
Specify the default priority level for the logged messages. Pass one of "emerg", "alert", "crit", "err", "warning", "notice", "info",
"debug", or a value between 0 and 7 (corresponding to the same named levels). These priority values are the same as defined by
syslog(3). Defaults to "info". Note that this simply controls the default, individual lines may be logged with different levels if they
are prefixed accordingly. For details, see --level-prefix= below.
--level-prefix=
Controls whether lines read are parsed for syslog priority level prefixes. If enabled (the default), a line prefixed with a priority
prefix such as "<5>" is logged at priority 5 ("notice"), and similar for the other priority levels. Takes a boolean argument.
EXIT STATUS
On success, 0 is returned, a non-zero failure code otherwise.
EXAMPLES
Example 1. Invoke a program
This calls /bin/ls with standard output and error connected to the journal:
# systemd-cat ls
Example 2. Usage in a shell pipeline
This builds a shell pipeline also invoking /bin/ls and writes the output it generates to the journal:
# ls | systemd-cat
Even though the two examples have very similar effects the first is preferable since only one process is running at a time, and both stdout
and stderr are captured while in the second example, only stdout is captured.
SEE ALSO
systemd(1), systemctl(1), logger(1)
systemd 237 SYSTEMD-CAT(1)