LISH(1)			NetBSD General Commands Manual		       LISH(1)

NAME
     lish -- a limited shell

SYNOPSIS
     lish [-Vx] [-c command]

DESCRIPTION
     lish implements a very simple, restricted command-line interpreter or
     shell.  Its goal is to allow execution of only a fixed set of commands,
     either interactively or read from standard in.

OPTIONS
     The following options are supported by lish:

     -V		 Print version number and exit.

     -c command	 Execute the given command.

     -x		 Enable tracing: Write each command to standard error, pre-
		 ceeded by '+'.

DETAILS
     lish is intended to allow severely restricted accounts to execute a lim-
     ited set of commands.  Its primary use case is non-interactive, and so
     lish does not implement many of the niceties available in common shells.
     Most notably, the features lish is intentionally not providing include
     I/O redirection, command-line history editing, and logical control opera-
     tors.

     When lish is invoked, it reads its configuration files (see section CON-
     FIGURATION FILES) to identify the commands it is allowed to execute.  It
     then reads commands from standard in, checks them against the list and,
     if they are allowed, executes them.  Multiple commands can be specified
     on a single line by separating them with a semicolon (';').  Note that
     any authorized commands following an unauthorized command in a command
     sequence will still be executed.

     In addition to restricting the commands a user can execute, lish also
     logs their invocation and whether or not the command was executed.

INPUT
     lish will determine which commands to execute (if they are allowed) in
     the following order:

     SSH_ORIGINAL_COMMAND   If this environment variable is set, lish will
			    interpret is as the command(s) to execute.	This
			    is to allow lish to be used in sshd(8) context via
			    the 'command=/usr/bin/lish' or 'ForceCommand'
			    restrictions.

     -c command		    Commands specified via the -c flag.	 This is the
			    typical invocation for a non-interactive login
			    shell from ssh(1).

     stdin		    If none of the above apply, lish will start in
			    interactive mode and read commands from standard
			    in.

BUILTINS
     lish contains the following builtins, which are always allowed:

     cd	   Change the current working directory.

     exit  Exit the current shell.

CONFIGURATION FILES
     lish first reads the file /etc/lishrc followed by the file
     /etc/lish/$USER (where $USER is the username of the user invoking lish)
     if it exists.

     The configuration file syntax is, like lish itself, intentionally sim-
     plistic:

     o	 the file is processed one line at a time

     o	 anything including and following a '#' is ignored

     o	 leading and trailing whitespace is ignored

     o	 each line may specify a single program with any optional command-line
	 flags

     o	 commands not beginning with a '/' are resolved using the fixed PATH
	 environment variable (see ENVIRONMENT)

     o	 to allow any and all command-line options, a '*' may be used

     o	 normal shell meta characters have no significance in lish

     o	 input/output redirection is not supported

ENVIRONMENT
     lish uses the SSH_ORIGINAL_COMMAND environment variable, as noted in the
     INPUT section.  At startup, lish will clear the environment and explic-
     itly set the following environment variables:

     PATH   /bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin

     USER   the output of getlogin(2)

     SHELL  the path of the executable

EXIT STATUS
     lish returns the exit status of the last command it executed or a status
     of 127 if the given command was not allowed.

SEE ALSO
     bash(1), ksh(1), syslog(3)

HISTORY
     lish was originally written by Jan Schaumann <jschauma@netmeister.org> in
     October 2014.

NetBSD 5.0			August 11, 2015			    NetBSD 5.0