01-02-2018
Pipelines only connect stdout to stdin of the next command and do nothing for stderr or other file descriptors. So
tee will only receive stdout of the first command and fiddling with file descriptors can only be used to combine them into stdout if you want their information to be used on the other side of the pipe.
Quote:
2.9.2 Pipelines
A pipeline is a sequence of one or more commands separated by the control operator '|'. The standard output of all but the last command shall be connected to the standard input of the next command.
The format for a pipeline is:
[!] command1 [ | command2 ...]
The standard output of command1 shall be connected to the standard input of command2. The standard input, standard output, or both of a command shall be considered to be assigned by the pipeline before any redirection specified by redirection operators that are part of the command (see Redirection).
Shell Command Language
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LEARN ABOUT OPENDARWIN
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)