\"
\" Copyright (c) 2003-2019
\" Jeffrey Allen Neitzel <jan (at) etsh (dot) nl>.
\" All rights reserved.
\"
\" Redistribution and use in source and binary forms, with or without
\" modification, are permitted provided that the following conditions
\" are met:
\" 1. Redistributions of source code must retain the above copyright
\" notice, this list of conditions and the following disclaimer.
\" 2. Redistributions in binary form must reproduce the above copyright
\" notice, this list of conditions and the following disclaimer in the
\" documentation and/or other materials provided with the distribution.
\"
\" THIS SOFTWARE IS PROVIDED BY JEFFREY ALLEN NEITZEL ``AS IS'', AND ANY
\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
\" DISCLAIMED. IN NO EVENT SHALL JEFFREY ALLEN NEITZEL BE LIABLE FOR ANY
\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
\" USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
\"
\" @(#)$Id: etsh.1,v 1.8 2019/03/14 08:50:46 jneitzel Exp $
\"
\" Derived from: V6 UNIX /usr/[doc/]man/man1/sh.1
\"
\" Copyright (C) Caldera International Inc. 2001-2002. All rights reserved.
\"
\" Redistribution and use in source and binary forms, with or without
\" modification, are permitted provided that the following conditions
\" are met:
\" 1. Redistributions of source code and documentation must retain the above
\" copyright notice, this list of conditions and the following disclaimer.
\" 2. Redistributions in binary form must reproduce the above copyright
\" notice, this list of conditions and the following disclaimer in the
\" documentation and/or other materials provided with the distribution.
\" 3. All advertising materials mentioning features or use of this software
\" must display the following acknowledgement:
\" This product includes software developed or owned by Caldera
\" International, Inc.
\" 4. Neither the name of Caldera International, Inc. nor the names of other
\" contributors may be used to endorse or promote products derived from
\" this software without specific prior written permission.
\"
\" USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA
\" INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR
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\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
\" POSSIBILITY OF SUCH DAMAGE.
\"
\" .SS Aliases (+) derived from:
\" - /usr/src/bin/csh/csh.1 (.Ss Alias substitution):
\" $OpenBSD: csh.1,v 1.66 2011/09/03 22:59:08 jmc Exp $
\" $NetBSD: csh.1,v 1.10 1995/03/21 09:02:35 cgd Exp $
\"
\" Copyright (c) 1980, 1990, 1993
\" The Regents of the University of California. All rights reserved.
\"
\" Redistribution and use in source and binary forms, with or without
\" modification, are permitted provided that the following conditions
\" are met:
\" 1. Redistributions of source code must retain the above copyright
\" notice, this list of conditions and the following disclaimer.
\" 2. Redistributions in binary form must reproduce the above copyright
\" notice, this list of conditions and the following disclaimer in the
\" documentation and/or other materials provided with the distribution.
\" 3. Neither the name of the University nor the names of its contributors
\" may be used to endorse or promote products derived from this software
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\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
\" SUCH DAMAGE.
\"
\" @(#)csh.1 8.2 (Berkeley) 1/21/94
\"
\" Includes public domain content derived from:
\" - /usr/src/bin/ksh/sh.1
\" $OpenBSD: sh.1,v 1.91 2011/09/03 22:59:08 jmc Exp $
\"
\" Includes content derived from /usr/src/bin/pwd/pwd.1 that documents
\" the etsh special built-in pwd command; the following license
\" covers it:
\"
\" $OpenBSD: pwd.1,v 1.21 2014/05/28 14:16:27 jmc Exp $
\" $NetBSD: pwd.1,v 1.10 1995/09/07 06:47:30 jtc Exp $
\"
\" Copyright (c) 1990, 1993
\" The Regents of the University of California. All rights reserved.
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\" the Institute of Electrical and Electronics Engineers, Inc.
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\" notice, this list of conditions and the following disclaimer.
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\" notice, this list of conditions and the following disclaimer in the
\" documentation and/or other materials provided with the distribution.
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\" may be used to endorse or promote products derived from this software
\" without specific prior written permission.
\"
\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
\" SUCH DAMAGE.
\"
\" @(#)pwd.1 8.2 (Berkeley) 4/28/95
\"
TH ETSH 1 "March 28, 2019" "etsh-5.4.0" "General Commands Manual"
SH NAME
etsh \- enhanced Thompson shell (command interpreter)
SH SYNOPSIS
B etsh
[\fB\-V\fR | \fB\-VV\fR]
br
B etsh
[\fB\-nv\fR]
[\fB\-\fR |
\fB\-c\fR [\fIstring\fR] |
\fB\-i\fR |
\fB\-l\fR |
\fB\-t\fR |
\fIfile\fR [\fIarg1 ...\fR]]
SH DESCRIPTION
B Etsh
is an enhanced,
backward-compatible port of the
standard command interpreter from Version 6 (V6) UNIX.
It may be used either as an interactive shell
or as a non-interactive shell.
Throughout this manual,
`(+)' indicates those cases where
B etsh
is known to differ from the original
IR sh (1),
as it appeared in Version 6 (V6) UNIX.
PP
The options are as follows:
TP
B \-
The shell reads and executes command lines
from the standard input until
end-of-file or
BR exit .
TP
\fB\-c\fR [\fIstring\fR]
If a
I string
is specified,
the shell executes it
as a command line and exits.
Otherwise,
the shell treats it as the
B \-
option.
TP
B \-i
(+)
The shell behaves as an interactive shell
by reading and executing commands from the
appropriate rc files if possible
(see
I "Startup\ and\ shutdown"
below)
before prompting the user, reading, and
executing command lines from the standard input.
The shell prints a diagnostic and exits with a
non-zero status if it is not connected to a terminal.
TP
B \-l
(+)
The shell behaves as a login shell
by reading and executing commands from the
appropriate rc files if possible
(see
I "Startup\ and\ shutdown"
below)
before prompting the user, reading, and
executing command lines from the standard input.
The shell prints a diagnostic and exits with a
non-zero status if it is not connected to a terminal.
TP
B \-n
(+)
IR noexec :
The shell performs no command-line execution.
It only checks the syntax of each command line,
after performing parameter substitution
and word splitting.
The shell ignores this option for interactive and login shells.
TP
B \-t
The shell reads a single command line
from the standard input,
executes it,
and exits.
TP
B \-v
(+)
IR verbose :
The shell prints the words of each command line
to the standard error,
after performing parameter substitution
and word splitting,
but before executing the resulting command line.
TP
B \-V
(+)
The shell prints its version from \fB$\fR\fIv\fR to
the standard output and exits.
TP
B \-VV
(+)
The shell prints its version from \fB$\fR\fIv\fR, and
build-time system information from `uname\ \-srm' (see
IR uname (1)),
to the standard output and exits.
PP
The shell may also be invoked non-interactively
to read, interpret, and execute a command file.
The specified
I file
and any arguments
are treated as positional parameters
(see
I "Parameter\ substitution"
below)
during execution of the command file.
PP
Otherwise,
if no arguments except for
B \-v
are specified and if both
the standard input and standard error are
connected to a terminal,
the shell is interactive.
By default,
an interactive shell prompts a regular user
with a `%\ ' or with a `#\ ' for the superuser
before reading each command line from the terminal.
(+) Notice that the user can set a non-default shell
prompt if desired
(see
I Prompt
below).
PP
(+) When an interactive shell starts,
it reads and executes commands
from the appropriate rc files if possible
(see
I "Startup\ and\ shutdown"
below)
before reading and executing command lines
from the terminal.
SS Metacharacters
A
I "syntactic metacharacter"
is any one of the following:
PP
RS 6
\fB|\fR
\fB^\fR
\fB;\fR
\fB&\fR
\fB(\fR
\fB)\fR
\fB<\fR
\fB>\fR
\fBspace\fR
\fBtab\fR
RE
PP
When such a character is unquoted,
it has special meaning to the shell.
The shell uses it to separate words
(see
I Commands
and
I "Command\ lines"
below).
A
I "quoting metacharacter"
is any one of the following:
PP
RS 6
\fB"\fR
\fB'\fR
\fB\\\fR
RE
PP
See
I "Quoting"
below.
The
I "substitution metacharacter"
is a:
PP
RS 6
\fB$\fR
RE
PP
See
I "Parameter\ substitution"
and
I "Variable\ substitution"
below.
Finally,
a
I "pattern metacharacter"
is any one of the following:
PP
RS 6
\fB*\fR
\fB?\fR
\fB[\fR
RE
PP
See
I "File\ name\ generation"
below.
SS Commands
Each command is a sequence of non-blank command arguments,
or words,
separated by one or more blanks (\fBspaces\fR or \fBtabs\fR).
The first argument specifies the name of a command to be executed.
Except for certain special arguments described below,
the arguments other than the command name are passed
without interpretation to the invoked command.
PP
If the first argument names a special command,
the shell executes it (see
I "Special\ commands"
below).
(+) Otherwise,
the shell treats it either as an alias
(see
I "Aliases"
below)
or as an external command,
which is located as follows.
PP
(+) If the command name contains no `/' characters,
the sequence of directories in the environment variable PATH
is searched for the first occurrence
of an executable file by that name,
which the shell attempts to execute.
However,
if the command name contains one or more `/' characters,
the shell attempts to execute it without
performing any PATH search.
PP
(+) If an executable file does not begin with
the proper magic number or a `#!shell' sequence,
it is assumed to be a shell command file,
and a new shell is automatically invoked to execute it.
The environment variable EXECSHELL
specifies the shell which is invoked
to execute such a file.
PP
If a command cannot be found or executed,
a diagnostic is printed.
SS Command lines
Commands separated by \fB|\fR or \fB^\fR constitute a chain of
IR filters ,
or a
IR pipeline .
The standard output of each command but the last
is taken as the standard input of the next command.
Each command is run as a separate process, connected
by pipes (see
IR pipe (2))
to its neighbors.
PP
A
IR "command\ line" ,
or
IR list ,
consists of one or more pipelines separated,
and perhaps terminated by \fB;\fR or \fB&\fR.
The semicolon designates sequential execution.
The ampersand designates asynchronous execution,
which causes the preceding pipeline to be executed
without waiting for it to finish.
The process ID of each command in such a pipeline is reported,
so that it may be used if necessary for a subsequent
IR kill (1).
PP
A list contained within parentheses such as
BI ( " list " )
is executed in a subshell and may appear
in place of a simple command as a filter.
PP
If a command line is syntactically incorrect,
a diagnostic is printed.
SS Termination reporting
All terminations other than exit and interrupt
are considered to be abnormal.
If a sequential process terminates abnormally,
a message is printed.
The termination report for an asynchronous process
is given upon execution of the first
sequential command subsequent to its termination,
or when the
B wait
special command is executed.
The following is a list of the possible
termination messages:
PP
nf
Hangup
Quit
Illegal instruction
Trace/BPT trap
IOT trap
EMT trap
Floating exception
Killed
Bus error
Memory fault
Bad system call
Broken pipe
fi
PP
For an asynchronous process,
its process ID is prepended to the appropriate message.
If a core image is produced,
`\ \-\-\ Core\ dumped' is appended
to the appropriate message.
SS I/O redirection
Each of the following argument forms
is interpreted as a
I redirection
by the shell itself.
Such a redirection may appear anywhere among
the arguments of a simple command,
or before or after a parenthesized command list,
and is associated with that command or command list.
PP
A redirection of the form \fB<\fR\fIarg\fR causes the file \fIarg\fR
to be used as the standard input (file descriptor 0)
for the associated command.
PP
A redirection of the form \fB>\fR\fIarg\fR causes the file \fIarg\fR
to be used as the standard output (file descriptor 1)
for the associated command.
If \fIarg\fR does not already exist, it is created;
otherwise, it is truncated at the outset.
PP
A redirection of the form \fB>>\fR\fIarg\fR is the same as \fB>\fR\fIarg\fR,
except if \fIarg\fR already exists the command output is
always appended to the end of the file.
PP
For example, either of the following command lines:
PP
nf
% date >index.txt ; pwd >>index.txt ; ls \-l >>index.txt
% ( date ; pwd ; ls \-l ) >index.txt
fi
PP
creates on the file `index.txt',
the current date and time,
followed by the name and a long listing
of the current working directory.
PP
(+) A \fB<\-\fR redirection causes input
for the associated command to be redirected
from the standard input which existed when
the shell was invoked.
This allows a command file to be used as a filter.
PP
A \fB>\fR\fIarg\fR or \fB>>\fR\fIarg\fR redirection associated with any
but the last command of a pipeline is ineffectual,
as is a \fB<\fR\fIarg\fR redirection with any but the first.
PP
The standard error (file descriptor 2)
is never subject to redirection by the shell itself.
Thus,
commands may write diagnostics to a location
where they have a chance to be seen.
However,
B fd2
provides a way to redirect the diagnostic output
to another location.
PP
If the file for a redirection cannot be opened or created,
a diagnostic is printed.
SS Quoting
The shell treats all
I single
(\fB'\fR)
and
I backslash
(\fB\\\fR)
I quoted
characters literally,
including characters which have
special meaning to the shell
(see
I Metacharacters
above).
If such characters are quoted,
they represent themselves and may be passed
as part of arguments.
PP
(+) Like the quoting behavior described above,
I double
(\fB"\fR) quotes
cause the shell to treat characters literally.
However,
double quotes also allow the shell to perform
parameter and variable substitution
via the dollar (\fB$\fR) metacharacter,
whereas
I single
(\fB'\fR) quotes
and
I backslash
(\fB\\\fR) quotes
do not.
PP
Individual characters, and sequences of characters,
are quoted when enclosed by a matched pair of
I double
(\fB"\fR) or
I single
(\fB'\fR) quotes.
For example:
PP
nf
% awk '{ print NR "\\t" $0 }' README ^ more
fi
PP
causes
IR awk (1)
to write each line from the `README' file,
preceded by its line number and a tab,
to the standard output which is piped to
IR more (1)
for viewing.
The outer single quotes prevent the shell from trying
to interpret any part of the string,
which is then passed as a single argument to awk.
PP
An individual
I backslash
(\fB\\\fR) quotes,
or
IR escapes ,
the next individual character.
A backslash followed by a newline is a special case
which allows continuation of command-line input
onto the next line.
Each backslash-newline sequence in the input
is translated into a blank.
PP
If a double or single quote appears
but is not part of a matched pair,
a diagnostic is printed.
SS Parameter substitution
When the shell is invoked with arguments besides
BR \-v ,
it has additional string processing capabilities
which are not otherwise available.
Such a shell may be invoked as follows:
PP
nf
\fBetsh\fR [\fB\-v\fR] \fIname\fR [\fIarg1 ...\fR]
fi
PP
If the first character of
I name
is not
BR \- ,
it is taken as the name of a
IR "command file" ,
or
IR "shell script" ,
which is opened as the standard input
for a new shell instance.
Thus,
the new shell reads and interprets command lines
from the named file.
PP
Otherwise,
I name
is taken as one of the shell options,
and a new shell instance is invoked
to read and interpret command lines
from its standard input.
However,
notice that the
B \-c
option followed by a
I string
is the one case where
the shell does not read and interpret command lines
from its standard input.
Instead,
the string itself is taken as a command line
and executed.
PP
In each command line,
an unquoted character sequence of the form \fB$\fR\fIN\fR,
where
I N
is a digit,
is treated as a
I "positional parameter"
by the shell.
Each occurrence of a positional parameter in the
command line is substituted with the value of the
\fIN\fRth argument to the invocation of the shell
(\fIargN\fR).
\fB$\fR\fI0\fR is substituted with
IR name .
PP
In all shell instances,
\fB$$\fR is substituted with the process ID of
the current shell.
The value is represented as a 5-digit ASCII string,
padded on the left with zeros when the process ID
is less than 10000.
PP
(+) All shell instances attempt to set
the special parameters in the following list.
`(*)' indicates those which are always set.
Otherwise,
the parameter is unset when the shell
cannot determine its value.
TP 10
\fB$\fR\fI#\fR (*)
The number of positional parameters currently available
to the shell.
TP
\fB$\fR\fI*\fR
The values of the positional parameters currently available
to the shell, from \fB$\fR\fI1\fR through the end of its argument list.
TP
\fB$\fR\fI?\fR (*)
The exit status of the last sequential command from the
I previous
command line.
TP
\fB$\fR\fId\fR
The value of the environment variable ETSHDIR.
TP
\fB$\fR\fIe\fR
The value of the environment variable EXECSHELL.
TP
\fB$\fR\fIg\fR
The effective group name of the current user,
as determined by
IR getgrgid (3).
The value (if any) is equivalent to that
given by `id\ \-gn'.
TP
\fB$\fR\fIh\fR
The value of the environment variable HOME.
TP
\fB$\fR\fIi\fR (*)
The effective group ID of the current user,
as determined by
IR getegid (2).
The value is equivalent to that given by `id\ \-g'.
TP
\fB$\fR\fIk\fR (*)
The effective user ID of the current user,
as determined by
IR geteuid (2).
The value is equivalent to that given by `id\ \-u'.
TP
\fB$\fR\fIm\fR
The value of the environment variable MANPATH.
TP
\fB$\fR\fIp\fR
The value of the environment variable PATH.
TP
\fB$\fR\fIs\fR
The value of the environment variable SHELL.
\" The full path name of the user's login shell.
TP
\fB$\fR\fIt\fR
The terminal name with which the standard input
was associated when the shell was invoked,
as determined by
IR ttyname (3).
The value (if any) is equivalent to that
given by `tty\ <\-'.
TP
\fB$\fR\fIu\fR
The effective user name of the current user,
as determined by
IR getpwuid (3).
The value (if any) is equivalent to that
given by `id\ \-un'.
TP
\fB$\fR\fIv\fR (*)
The version of the current shell represented
as a one-word, read-only string.
TP
\fB$\fR\fIw\fR
The value of the environment variable CWD.
It is the absolute physical path name of the
current working directory, without symbolic links,
as determined by
IR getcwd (3).
On error,
the value of $w is set to the empty string.
PP
All substitution on a command line is performed
I before
the line is interpreted.
Thus,
no action which alters the value of any parameter
can have any effect on a reference to that parameter
occurring on the
I same
line.
PP
A positional-parameter value may contain
any number of metacharacters.
Each one which is
IR unquoted ,
or
IR unescaped ,
within a positional-parameter value retains
its special meaning when the value is substituted
in a command line by the invoked shell.
PP
Take the following two shell invocations for example:
PP
nf
% etsh \-c '$1' 'echo Hello World! >/dev/null'
% etsh \-c '$1' 'echo Hello World! \\>/dev/null'
Hello World! >/dev/null
fi
PP
In the first invocation,
the \fB>\fR in the value substituted by \fB$\fR\fI1\fR
retains its special meaning.
This causes all output from
B echo
to be redirected to \fI/dev/null\fR.
However,
in the second invocation,
the meaning of \fB>\fR is
I escaped
by \fB\\\fR
in the value substituted by \fB$\fR\fI1\fR.
This causes the shell to pass `>/dev/null'
as a single argument to echo instead of interpreting
it as a redirection.
SS Variable substitution (+)
The shell can substitute variables;
a user may cause the shell to unset and set
variables by using the
B unset
and
B set
special commands.
PP
Variables may be used both in interactive shells
and in non-interactive shells.
However,
notice that variables are not functional
when a non-interactive shell is invoked
either with the
B \-c
option followed by a
I string
or with the
B \-t
option.
Such a shell only executes one command line,
but setting and using a variable requires
executing two command lines in the same shell,
one to set it and one to use it.
PP
A variable can either be unset or set.
When unset, a variable has no \fIvalue\fR.
When set,
a variable has both \fIname\fR and \fIvalue\fR.
A valid variable \fIname\fR is
a single ASCII character,
which matches either the [A-Z] range
or the [a-cfjlnoq-sx-z] range,
inclusive.
A valid variable \fIvalue\fR can be anything from
an empty string, denoted by "" or '', to whatever
you can input into a syntactically correct command line
with less than or equal to the maximum command line length
of characters, 2048 for the sake of brevity.
PP
For example,
`set\ C\ value' sets the variable C to value, as you can see
in the following examples.
PP
nf
% : Example One
% unset C
% set C
% if $? -eq 1 -a "$C" = "C" echo 'C is unset.'
C is unset.
% : Example Two
% set C ''
% ( set C ) >/dev/null
% if $? -eq 0 -a -z "$C" echo 'C == "'"$C"'"'
C == ""
% set W "Hello "
% set W "$WWorld!"
% if "$W" != "W" -a -n "$W" echo "$W"
Hello World!
% : Example Three
% alias now "date '+%A, %Y-%m-%d, %T %Z';:"
% alias loadavg "echo \-n $H': ';\\
uptime|sed 's/^.*user[s,][ ,] *//';:"
% set C '( now ; loadavg )' ; : 'C == Command Line (or List)'
% ( set C ) >/dev/null
% if $? -eq 0 -a -n "$C" echo "C == `$C'"
C == `( now ; loadavg )'
% $C | awk '{ print NR "\\t" $0 }'
1 Saturday, 2018-02-24, 21:52:03 UTC
2 refugio: load averages: 0.54, 0.22, 0.08
fi
PP
As with parameters
(see
I "Parameter\ substitution"
above),
all substitution on a command line is performed
I before
the line is interpreted.
Thus,
no action which alters the value of any variable
can have any effect on a reference to that variable
occurring on the
I same
line.
PP
Also,
a variable value may contain
any number of metacharacters.
Each one which is
IR unquoted ,
or
IR unescaped ,
within a variable value retains
its special meaning when the value
is substituted in a command line.
PP
If a variable name passed as an argument to
B set
or
B unset
is invalid,
a diagnostic is printed.
Similarly,
if a variable value causes an error,
a diagnostic is printed.
SS File name generation
Prior to executing a command,
the shell scans each argument for
unquoted \fB*\fR, \fB?\fR, or \fB[\fR characters.
If one or more of these characters appears,
the argument is treated as a
I pattern
and causes the shell to search for file names which
I match
it.
Otherwise,
the argument is used as is.
PP
The meaning of each pattern character is as follows:
IP o 4
The \fB*\fR character in a pattern matches any string of
characters in a file name (including the null string).
IP o
The \fB?\fR character in a pattern matches any single character
in a file name.
IP o
The \fB[...]\fR brackets in a pattern specifies a class of characters
which matches any single file-name character in the class.
Within the brackets,
each character is taken to be a member of the class.
A pair of characters separated by an unquoted \fB\-\fR specifies
the class as a range which matches each character lexically
between the first and second member of the pair, inclusive.
A \fB\-\fR matches itself when quoted or when first or last
in the class.
PP
Any other character in a pattern matches itself in a file name.
PP
Notice that the `.' character at the beginning of a file name,
or immediately following a `/',
is always special in that it must be matched explicitly.
The same is true of the `/' character itself.
PP
If the pattern contains no `/' characters,
the current directory is always used.
Otherwise,
the specified directory is the one obtained by taking the pattern
up to the last `/' before the first unquoted \fB*\fR, \fB?\fR, or \fB[\fR.
The matching process matches the remainder of the pattern
after this `/' against the files in the specified directory.
PP
In any event,
a list of file names is obtained from the current
(or specified) directory which match the given pattern.
This list is sorted in ascending ASCII order,
and the new sequence of arguments
replaces the given pattern.
The same process is carried out for each
of the given pattern arguments;
the resulting lists are
I not
merged.
Finally,
the shell
attempts to execute the command
with the resulting argument list.
PP
If a pattern argument refers to
a directory which cannot be opened,
a `No\ directory' diagnostic is printed.
PP
If a command has only
I one
pattern argument,
a `No\ match' diagnostic is printed if it fails
to match any files.
However,
if a command has more than one pattern argument,
a diagnostic is printed only when they
I all
fail to match any files.
Otherwise,
each pattern argument failing to match
any files is removed from the argument list.
SS Startup and shutdown (+)
If the first character of the argv[0] used to
invoke an interactive shell is `\-' (e.g.,\ \-etsh),
it is a login shell and tries to read and execute commands
from the following four rc init files in sequence:
IR /usr/local/etc/etsh.login ,
IR /usr/local/etc/etsh.etshrc ,
IR $h/.etsh.login ,
and
IR $h/.etshrc .
The same is true when the shell is invoked with the
B \-l
option,
regardless of the value of argv[0].
PP
In the case where an interactive shell is not
a login shell according to its argv[0],
it tries to read and execute commands
from the following two rc init files in sequence:
I /usr/local/etc/etsh.etshrc
and
IR $h/.etshrc .
The same is true when the shell is invoked with the
B \-i
option,
regardless of the value of argv[0].
PP
In any case,
after the shell finishes its startup actions,
it then prompts the user, reads, and executes
command lines from the standard input as usual.
PP
If the shell is invoked as a login shell,
it tries to read and execute commands from
I /usr/local/etc/etsh.logout
and
I $h/.etsh.logout
in sequence upon logout.
These two rc logout files may be used if necessary
for cleanup upon termination of a login session by
an EOT (see
I "End\ of\ file"
below)
or a SIGHUP signal (see
I "Signals"
below).
PP
Notice that
the shell only performs the startup and shutdown actions
described above for readable, regular rc files.
If any rc file is
I not
readable,
the shell ignores it and continues as normal.
If any rc file is
I not
a regular file (or a link to a regular file),
the shell ignores it, prints a diagnostic,
and continues as normal.
PP
In the normal case,
a SIGINT or SIGQUIT signal received by the shell
during execution of any rc file causes
it to cease execution of that file
without terminating.
Thus,
it may be desirable to use the
B trap
special command to ignore these
and other signals in some cases.
For example,
this is particularly true for
IR /usr/local/etc/etsh.login ,
IR /usr/local/etc/etsh.etshrc ,
and
IR /usr/local/etc/etsh.logout .
PP
The
B exit
special command
always causes the shell to terminate if it occurs
in any rc file.
SS History (+)
If the shell is invoked as an interactive shell,
it tries to open the
I $h/.etsh.history
file to save the user's command-line history.
Notice that the history file must already exist
as a writable,
regular file (or a link to a regular file)
when the shell is invoked to save
the user's command-line history.
Otherwise,
it will not do so.
PP
An interactive shell reads each command line from
its terminal and appends the words of each one to
the history file as a line after performing
parameter substitution and word splitting.
PP
The shell does not read the history file or have any features
that allow the user to make direct use of the saved history.
Such features are available via standard external commands
and also via the
B history
command found in the \fI/usr/local/libexec/etsh-5.4.0/etsh\fR directory.
Execute `history \-h' to read its documentation.
PP
Notice that the shell never creates or removes the
I $h/.etsh.history
file.
It always leaves these actions to the user.
For example:
PP
nf
% history -r ; history -c ; exec etsh -l
fi
PP
causes
B history
to remove the existing history file (if any),
to create a new (empty) one, and causes
the current shell to replace itself with
a new login shell,
while opening the new history file.
This,
and future,
interactive shells then save the user's
command-line history as long as
the history file exists.
PP
If desired,
the user can use the history file to repeat
any command line as a command substitution with
IR sed (1)
and
BR etsh .
Taking the following command line
and history entry for example:
PP
nf
% history -n 6171
Number Command Line
------ ------------
6171 uname -s | if { fd2 -ef/dev/null \\
egrep '([ONF][a-z]{2,3}BSD|Darwin|Linux)' } \\
echo '(Open|Net|Free)BSD || (Mac) OS X || OS == GNU/Linux'
fi
PP
and then doing a:
PP
nf
% sed -n 6171p <$h/.etsh.history | etsh
OS == GNU/Linux || (Mac) OS X || (Free|Net|Open)BSD
(Open|Net|Free)BSD || (Mac) OS X || OS == GNU/Linux
fi
PP
causes sed to output the 6171st command line from
the history file via pipe for repetition as a
command substitution by etsh.
SS Aliases (+)
The shell can interpret command aliases set by the user.
A user may cause the shell to set, print, and unset
command aliases by using the
B alias
and
B unalias
special commands.
PP
A command alias is a string that substitutes
for a given command alias name set by the user.
Command aliases provide a simple way to represent
complex, long, or often-used commands
as simple command names.
Thus,
if the first argument names an existing command alias,
its alias string substitutes for the command alias name.
Any remaining arguments are appended to the argument list.
PP
Aliases may be used both in interactive shells
and in non-interactive shells.
However,
notice that aliases are not functional
when a non-interactive shell is invoked
either with the
B \-c
option followed by a
I string
or with the
B \-t
option.
Such a shell only executes one command line,
but setting and using an alias requires
executing two command lines in the same shell,
one to set it and one to execute it.
PP
The shell parses each alias in a command line
into a list of words from left to right,
wraps it as a
\fB(\fR\ \fIlist\fR\ \fB)\fR,
re-parses it while parsing any nested aliases
(up to three deep),
and executes the resulting alias in a subshell
on success.
Three examples of alias usage follow:
PP
nf
% : Example One
% alias s 'echo $?;:' ; alias status 's'
% alias s ; alias status
(echo $?;:)
(s)
% false
% status
1
% : Example Two
% alias ll 'ls \-AlF'
% alias ll
(ls \-AlF)
% ll \-d [A\-Z]* | wc \-l | tr \-d ' \\t'
10
% : Example Three
% alias loadavg "uname \-n|sed 's/\\([^.]*\\).*/\\1/'|tr -d \\\\n;\\
echo \-n ': ';uptime|sed 's/^.*user[s,][ ,] *//';:"
% alias loadavg
(uname \-n|sed 's/\\([^.]*\\).*/\\1/'|tr -d \\\\n;\\
echo \-n ': ';uptime|sed 's/^.*user[s,][ ,] *//';:)
% loadavg | awk '{ print NR "\\t" $0 }'
1 serenity: load average: 0.49 0.39 0.29
fi
PP
If an alias,
or its parsed result in a command line,
is syntactically incorrect,
a diagnostic is printed.
If an alias loop error occurs,
a `Too\ many\ nested\ aliases' diagnostic is printed.
SS Prompt (+)
PP
The state of the \fR\fBP\fR \fIvariable\fR determines
how the shell prompt appears.
The user can return to the default prompt
by executing `unset\ P' whenever desired.
Since P is a variable,
see
I "Variable\ substitution"
above,
as the same documentation
applies here too.
PP
Notice that `set\ P\ string' sets the
shell prompt to string.
See
B SetP
in the \fI/usr/local/libexec/etsh-5.4.0/etsh\fR directory.
You can
B source
or
B \.
it if you wish to use it.
PP
Four examples of setting your prompt follow:
PP
nf
% : Example One
% : " This is the default prompt, but let's " ; unset P ;\\
: " it to be sure. I am not root now, as you can see. "
%
% : Example Two
% : " OK, let's see others. "
% set P '=\\^\\) hello \\(\\^=\\>% '
=^) hello (^=>%
% : Example Three
=^) hello (^=>% : " Silly! Others? OK. "
=^) hello (^=>% . SetP "$u:p2\\>"
jneitzel:p2>%
% : Example Four
jneitzel:p2>% : " Or with $w and 2 more lines? OK. "
jneitzel:p2>% . $h/.etsh.prompt
~/src/git/v6shell
jneitzel@refugio
p2>%
~/src/git/v6shell
jneitzel@refugio
p2>% : " In effect, the '. $h/etsh.prompt' above prepares \\
things before doing a special '. SetP string'. "
~/src/git/v6shell
jneitzel@refugio
p2>%
fi
PP
Notice that an
I $h/.etsh.prompt
file
is not required in order to set and use a personal etsh prompt.
That said,
it can make things simpler or easier,
in the same way that having an $h/.etshrc file can do so.
In any case,
I trust you noticed that "Example\ Two" above did not mention
or use $h/.etsh.prompt at all; it was completely manual.
PP
Now, while the included .etsh.prompt file is admittedly
too complex with 74 lines, a simpler and shorter file
can be quite effective if your prompt objective is more
focused than mine is, or was, when I wrote it.
PP
Documenting all of the appropriate bits here in
the manual was quite a challenge.
Hopefully, I have not added unnecessary
complexity and confusion.
That said,
if you find room for improvement,
I invite you to send me your suggestions.
SS End of file
An end-of-file in the shell's input
causes it to exit.
If the shell is interactive,
this means it exits by default when
the user types an EOT (^D) at the prompt.
If desired,
the user may change or disable
interactive shell EOT exit behavior with
IR stty (1).
SS Special commands
The shell treats the following built-in commands specially.
TP
\fB:\fR [\fIarg ...\fR]
Does nothing and sets the exit status to zero.
TP
\fBalias\fR [\fIname\fR [\fIstring\fR]] (+)
Sets the alias \fIname\fR to \fIstring\fR in the current shell
if both \fIname\fR and \fIstring\fR are specified.
Prints the current value of the alias \fIname\fR's string
if \fIname\fR is specified and set in the current shell.
Prints the name and string of each alias set in
the current shell if no arguments are specified.
TP
\fBcd\fR [\fIdir ...\fR] (+)
Is a synonym for the
B chdir
special command.
TP
\fBchdir\fR [\fIdir ...\fR]
Changes the shell's current working directory to
IR dir .
(+) If
I dir
is an unquoted \fB-\fR,
the shell's previous working directory is used instead.
Otherwise,
if
I dir
is not specified,
the user's home directory is used by default.
TP
\fBecho\fR [\fB\-n\fR] [\fIstring ...\fR] (+)
Writes its string arguments (if any) separated by blanks
and terminated by a newline to the standard output.
If \fB\-n\fR is specified, the terminating newline is not written.
TP
\fBexec\fR \fIcommand\fR [\fIarg ...\fR] (+)
Replaces the current shell with an instance of
IR command ,
which must be external to the shell.
TP
B exit
Causes the shell to cease execution of a file.
This means exit has no effect at the prompt
of an interactive shell.
TP
\fBfd2\fR [\fB\-e\fR] [\fB\-f\fR \fIfile\fR] [\fB\-\-\fR] \fIcommand\fR [\fIarg ...\fR] (+)
Redirects from/to file descriptor 2 for
IR command .
See the
IR fd2 (1)
manual page for full details.
TP
\fBgoto\fR \fIlabel\fR [\fI...\fR] (+)
Transfers shell control to the `\fB:\fR \fIlabel\fR' line
of the current command file.
See the
IR goto (1)
manual page for full details.
TP
\fBhistory\fR [\fB\-c\fR | \fB\-h\fR | \fB\-l\fR | \fB\-n\fR \fInumber1\fR[\fI,number2\fR] | \fB\-p\fR \fIpattern\fR | \fB\-r\fR] (+)
Manages, prints, and searches the user's \fI$h/.etsh.history\fR file.
If no options are specified,
the history command prints all history entries from
the user's etsh history file to the standard output.
Execute `history \-h' to read its documentation.
TP
\fBif\fR [\fIexpression\fR [\fIcommand\fR [\fIarg ...\fR]]] (+)
Evaluates
IR expression ,
conditionally executes
IR command ,
and sets the exit status to zero or non-zero
as appropriate.
See the
IR if (1)
manual page for full details.
TP
\fBlogin\fR [\fIarg ...\fR]
Replaces the current interactive shell with
IR login (1).
TP
\fBnewgrp\fR [\fIarg ...\fR]
Replaces the current interactive shell with
IR newgrp (1).
TP
\fBprompt\fR [\fIon\fR | \fIdebug\fR | \fIoff\fR] (+)
Sets the shell's current prompt state to
IR on ,
IR debug ,
or
IR off ,
or prints its current value.
The prompt command helps manage the shell's different prompt
behaviors on the user's behalf. When on, it enables personal,
non-default, shell prompts.
When set to debug, it enables some extra functionality that can
help in seeing what the shell is doing to convert $P string
into a personal prompt.
When off, the shell uses its default prompts.
An exit status of 2 indicates error.
TP
\fBpwd\fR (+)
Prints the absolute physical pathname of the current working
directory to the standard output. An exit status of 2
indicates that
IR getcwd (3)
detected an error, or that pwd itself detected a usage error.
TP
\fBset\fR [\fIname\fR [\fIvalue\fR]] (+)
Sets the variable \fIname\fR to the string \fIvalue\fR in the
current shell if both \fIname\fR and \fIvalue\fR are specified.
Prints the current value of variable \fIname\fR
if \fIname\fR is specified and set in the current shell.
Prints the name and value of each variable set in
the current shell if no arguments are specified.
TP
\fBsetenv\fR \fIname\fR \fIvalue\fR (+)
Sets the environment variable \fIname\fR to
the string \fIvalue\fR.
TP
B shift
Shifts all positional-parameter values to the
left by 1,
so that the old value of \fB$\fR\fI2\fR becomes the new
value of \fB$\fR\fI1\fR and so forth.
The value of \fB$\fR\fI0\fR does not shift.
TP
\fB.\fR \fIfile\fR [\fIarg1 ...\fR] (+)
Is a synonym for the
B source
special command.
TP
\fBsource\fR \fIfile\fR [\fIarg1 ...\fR] (+)
Causes the shell to read and execute commands
from the specified \fIfile\fR and return.
If the file name contains no `/' characters,
the sequence of directories in the environment
variable PATH is searched for the first occurrence
of a file by that name.
However,
if the file name contains one or more `/' characters,
the shell attempts to source it without performing
any PATH search.
Notice that the file does not need to be executable.
The file and any arguments
are treated as positional parameters
(see
I "Parameter\ substitution"
above)
during execution of the file.
The source command may be nested.
As with command files,
most shell-detected errors cause the shell
to cease execution of the file.
If the source command is nested and
such an error occurs,
all nested source commands terminate.
TP
\fBtrap\fR [\fB''\fR | \fB:\fR | \fB\-\fR \fIsignal_number ...\fR] (+)
\fB''\fR or \fB:\fR causes the specified signals
to be ignored if possible,
and \fB\-\fR causes the specified signals
to be reset to the default action if possible.
If a signal was already ignored when
the shell was invoked,
\" it can never be reset with \fB-\fR.
it cannot be reset with \fB-\fR.
If no arguments are specified,
a list is printed of those signals which
are ignored by trap in the current shell context.
TP
\fBumask\fR [\fImask\fR] (+)
Sets the file creation mask (see
IR umask (2))
to the octal value specified by
IR mask .
If the mask is not specified,
its current value is printed.
TP
\fBunalias\fR \fIname\fR \fI...\fR (+)
Removes each of the specified alias \fInames\fR from
the current shell instance.
TP
\fBunset\fR \fIname\fR \fI...\fR (+)
Removes each of the specified variable \fInames\fR
from the current shell instance.
TP
\fBunsetenv\fR \fIname\fR \fI...\fR (+)
Removes each of the specified environment variable \fInames\fR
from the environment of the current shell instance.
TP
\fBverbose\fR [\fItrue\fR | \fIfalse\fR] (+)
Sets the shell's current verbose state to
I true
or
IR false ,
or prints its current value.
When true, the shell is verbose, as it is when invoked
with the
B \-v
option.
Otherwise, it is not verbose.
Its exit status indicates the current value
of 0 for true or 1 for false, with 2 indicating error.
This may be tested with the
B if
command.
TP
B wait
Waits for all asynchronous processes to terminate,
reporting on abnormal terminations.
SS Signals (+)
An interactive or login shell always ignores
the SIGINT, SIGQUIT, and SIGTERM signals (see
IR signal (3)).
A login shell also handles the SIGHUP signal,
the receipt of which causes the shell to terminate
the login session and to read and execute
its rc logout files if possible.
PP
If SIGHUP, SIGINT, SIGQUIT, or SIGTERM is already ignored
when the shell starts,
it is also ignored by the current shell and all of its
child processes.
Otherwise,
SIGINT and SIGQUIT are reset to the
default action for sequential child processes,
whereas SIGHUP and SIGTERM are reset to the default action
for all child processes.
PP
When a non-interactive shell executes a command file,
it does not handle or ignore any signal by default.
Any other non-interactive shell ignores SIGINT and SIGQUIT.
PP
For any signal not mentioned above,
the shell inherits the signal action (default or ignore)
from its parent process and passes it to its child processes.
Remember that the
B trap
special command may be used to ignore signals
when the shell does not do so by default.
PP
Asynchronous child processes always ignore
both SIGINT and SIGQUIT.
Also,
if such a process has not redirected its
input with a \fB<\fR, \fB|\fR, or \fB^\fR,
the shell automatically redirects it to come from
IR /dev/null .
SH "EXIT STATUS (+)"
The exit status of the shell is generally that of
the last command executed prior to end-of-file or
BR exit .
PP
However,
if the shell is interactive and detects an error,
it exits with a non-zero status if the user
types an EOT at the next prompt.
PP
Otherwise,
if the shell is non-interactive and is reading
commands from a file,
any shell-detected error causes the shell
to cease execution of that file.
This results in a non-zero exit status.
PP
A non-zero exit status returned by the shell
itself is always one of the values described
in the following list,
each of which may be accompanied
by an appropriate diagnostic:
TP
2
The shell detected a syntax, redirection,
or other error not described in this list.
TP
125
An external command was found
but did not begin with the proper
magic number or a `#!shell' sequence,
and a valid shell was not specified by
EXECSHELL with which to execute it.
TP
126
An external command was found
but could not be executed.
TP
127
An external command was not found.
TP
>128
An external command was terminated by a signal.
SH "ENVIRONMENT (+)"
Notice that the concept of `user environment'
was not defined in Version 6 (V6) UNIX.
Thus,
use of the following environment variables
by this port of the shell is an enhancement:
TP
B CWD
The shell sets the value of this variable while
setting the \fB$\fR\fIw\fR special parameter.
Both represent the absolute physical path name
of the current working directory, without symbolic links.
On error,
CWD is removed from the environment.
TP
B ETSHDIR
If set to a non-empty string,
the value of this variable is taken as the
path name of a directory which may be used
for temporary files.
Its value is available to the shell via
the \fB$\fR\fId\fR special parameter.
TP
B EXECSHELL
If set to a non-empty string,
the value of this variable is taken as the
path name of the shell which is invoked to
execute an external command when it does not
begin with the proper magic number
or a `#!shell' sequence.
Its value is available to the shell via
the \fB$\fR\fIe\fR special parameter.
TP
B HOME
If set to a non-empty string,
the value of this variable is taken as the
user's home directory.
Its value is available to the shell via
the \fB$\fR\fIh\fR special parameter and is
the default directory for the
B chdir
special command.
TP
B MANPATH
If set,
the value of this variable is taken as the
sequence of directories used by
IR man (1)
to search for manual page files.
Its value is available to the shell via
the \fB$\fR\fIm\fR special parameter.
TP
B PATH
If set to a non-empty string,
the value of this variable is taken as the
sequence of directories used
by the shell to search both for external commands
and for files to be executed by the
B source
special command.
Its value is available to the shell via
the \fB$\fR\fIp\fR special parameter.
Notice that the Version 6 (V6) UNIX
shell always used the equivalent of `.:/bin:/usr/bin',
not PATH.
TP
B SHELL
If set to a non-empty string,
the value of this variable is taken as the
full path name of the user's login shell.
Its value is available to the shell via
the \fB$\fR\fIs\fR special parameter.
SH FILES
TP
I /dev/null
default source of input for asynchronous processes
TP
IR /usr/local/etc/etsh.login \ (+)
system-wide rc init file for login shells
TP
IR /usr/local/etc/etsh.etshrc \ (+)
system-wide rc init file for \fIall\fR interactive shells
TP
IR $h/.etsh.history \ (+)
user history file for \fIall\fR interactive shells
TP
IR $h/.etsh.login \ (+)
user rc init file for login shells
TP
IR $h/.etshrc \ (+)
user rc init file for \fIall\fR interactive shells
TP
IR /usr/local/etc/etsh.logout \ (+)
system-wide rc logout file for login shells
TP
IR $h/.etsh.logout \ (+)
user rc logout file for login shells
TP
IR $h/.etsh.prompt \ (+)
user etsh prompt preprocessor for interactive etsh instances.
It supports the
B prompt
special command.
In effect, it serves as an interface
between the shell and the SetP script.
SH "SEE ALSO"
awk(1),
env(1),
expr(1),
fd2(1),
goto(1),
grep(1),
if(1),
kill(1),
login(1),
man(1),
newgrp(1),
sed(1),
stty(1),
tsh(1),
uname(1)
PP
Etsh home page:
https://etsh.nl/
PP
`The UNIX Time-Sharing System' (CACM, July, 1974):
PP
nf
https://etsh.nl/history/unix/
fi
PP
gives the theory of operation of both the system and the shell.
SH HISTORY
A
B sh
command
appeared as
I /bin/sh
in Version 1 (V1) UNIX.
PP
The Thompson shell
was used as the standard command interpreter
through Version 6 (V6) UNIX.
Then,
in Version 7 (V7) UNIX,
it was replaced by the Bourne shell.
However,
the Thompson shell
was still distributed with the system as
B osh
because of known portability problems
with the Bourne shell's memory management
in Version 7 (V7) UNIX.
SH AUTHORS
This port of the Thompson shell is derived from
Version 6 (V6) UNIX /usr/source/s2/sh.c,
which was principally written by Ken Thompson of Bell Labs.
Jeffrey Allen Neitzel
RI <
[email protected] >
ported and maintains it as
IR tsh (1).
Jeffrey also ported and maintains
this enhanced port of the Thompson shell as
IR etsh (1).
SH LICENSE
See either the LICENSE file which is distributed with
B etsh
or
https://etsh.nl/license/
for full details.
SH CAVEATS
Unlike the original,
this port of the shell can handle 8-bit character
sets, as well as the UTF-8 encoding.
The original,
on the other hand,
can only handle 7-bit ASCII.
PP
Notice that certain shell oddities were historically
undocumented in this manual page.
Particularly noteworthy is the fact that there
is no such thing as a usage error.
Thus,
the following shell invocations are all perfectly valid:
PP
nf
etsh \-cats_are_nice!!! ': "Good kitty =)"'
etsh \-tabbies_are_too!
etsh \-s
fi
PP
The first two cases correspond to the
B \-c
and
B \-t
options
respectively;
the third case corresponds to the
B \-
option.
SH "BUGS (+)"
The shell differentiates between an
end-of-file and an error returned by the
IR read (2)
system call.
This allows the shell to print a diagnostic
and exit with a non-zero status if appropriate.
Previously, it did not recover
from read(2) errors and exited
when this system call failed,
and this is still true today.
SH "SECURITY CONSIDERATIONS"
This port of the Thompson shell does not support set-ID execution.
If the effective user (group) ID of the shell process is not equal
to its real user (group) ID when an instance of it starts up,
the shell prints the following diagnostic and exits with
a non-zero status.
PP
nf
Set-ID execution denied
fi
PP
If the shell did support set-ID execution,
it could possibly allow a user to violate the
security policy on a host where the shell is used.
For example,
if the shell were running a setuid-root command file,
a regular user could possibly invoke an interactive
root shell as a result.
PP
This is
I not
a bug.
It is simply how the shell works.
Thus,
B etsh
does not support set-ID execution.
This is a proactive measure to avoid problems,
nothing more.
