OpenSSH SSH client (remote login program)
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-A Enables forwarding of the authentication agent connection. This can also be specified on a per-
host basis in a configuration file.
Agent forwarding should be enabled with caution. Users with the ability to bypass file permissions
on the remote host (for the agent's UNIX-domain socket) can access the local agent through the
forwarded connection. An attacker cannot obtain key material from the agent, however they can
perform operations on the keys that enable them to authenticate using the identities loaded into
the agent.
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-C Requests compression of all data (including stdin, stdout, stderr, and data for forwarded X11 and
TCP connections). The compression algorithm is the same used by gzip(1), and the “level” can be
controlled by the CompressionLevel option for protocol version 1. Compression is desirable on
modem lines and other slow connections, but will only slow down things on fast networks. The
default value can be set on a host-by-host basis in the configuration files; see the Compression
option.
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-q Quiet mode. Causes most warning and diagnostic messages to be suppressed.
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ssh connects and logs into the specified hostname (with optional user name). The user must prove his/her
identity to the remote machine using one of several methods depending on the protocol version used (see
below).
If command is specified, it is executed on the remote host instead of a login shell.
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Pipelines
A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The
format for a pipeline is:
[time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
The standard output of command is connected via a pipe to the standard input of command2. This
connection is performed before any redirections specified by the command (see REDIRECTION below). If |&
is used, the standard error of command is connected to command2's standard input through the pipe; it is
shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any
redirections specified by the command.
The return status of a pipeline is the exit status of the last command, unless the pipefail option is
enabled. If pipefail is enabled, the pipeline's return status is the value of the last (rightmost)
command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word
! precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status as
described above. The shell waits for all commands in the pipeline to terminate before returning a value.
If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by
its execution are reported when the pipeline terminates. The -p option changes the output format to that
specified by POSIX. When the shell is in posix mode, it does not recognize time as a reserved word if
the next token begins with a `-'. The TIMEFORMAT variable may be set to a format string that specifies
how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables
below.
When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children. The TIMEFORMAT variable may be used
to specify the format of the time information.
Each command in a pipeline is executed as a separate process (i.e., in a subshell).
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The GNU version of the tar archiving utility
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-x, --extract, --get
extract files from an archive
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-v, --verbose
verbosely list files processed
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