Bourne shell history + tilde + job control + more (Part 9 of 9)
sources-request at genrad.UUCP
sources-request at genrad.UUCP
Wed Jun 12 21:49:14 AEST 1985
From: Arnold Robbins <gatech!arnold>
This is part 9 of 9. It contains the diffs for the manual page for the
System V Release 2 Bourne shell that comes with BRL Unix. The original
man page is in /usr/5lib/man/u_man/man1/sh.1.
Arnold Robbins
arnold at gatech.{UUCP, CSNET}
--------------- You know what to do here -----------------------
*** ../orig.u/sh.1 Wed May 15 17:22:38 1985
--- sh.1 Wed Jun 5 11:08:21 1985
***************
*** 34,40
.SH SYNOPSIS
.B sh
[
! .B \-acefhiknrstuvxEIJ
] [ args ]
.SH DESCRIPTION
.I Sh\^
--- 34,40 -----
.SH SYNOPSIS
.B sh
[
! .B \-acefhiknqrstuvxEHIJ
] [ args ]
.SH DESCRIPTION
.I Sh\^
***************
*** 62,67
.BR ? ,
.BR \- ,
.BR $ ,
and
.BR !\\^ .
.SS Commands
--- 62,68 -----
.BR ? ,
.BR \- ,
.BR $ ,
+ .BR + ,
and
.BR !\\^ .
.SS Commands
***************
*** 436,441
.B $
The process number of this shell.
.TP
.B !
The process number of the last background command invoked.
.PD
--- 437,454 -----
.B $
The process number of this shell.
.TP
+ .B +
+ The process number of the parent of this shell. In particular,
+ the value of
+ .B $+
+ will track the value of the
+ .IR getppid (2)
+ system call. I.e. if
+ .I init
+ should inherit this shell,
+ .B $+
+ will become 1.
+ .TP
.B !
The process number of the last background command invoked.
.PD
***************
*** 525,530
\f3\s-1PS1\s+1\fP
prompt causes the shell to auto-terminate.
Set to 0 to disable this BRL feature.
.PD
.RE
.PP
--- 538,549 -----
\f3\s-1PS1\s+1\fP
prompt causes the shell to auto-terminate.
Set to 0 to disable this BRL feature.
+ .TP
+ .B
+ .SM HISTFILE
+ The file where command history is saved across login sessions.
+ The default value is
+ .BR \s-1$HOME\s+1/.history .
.PD
.RE
.PP
***************
*** 529,535
.RE
.PP
The shell gives default values to
! \f3\s-1PATH\s+1\fP, \f3\s-1PS1\s+1\fP, \f3\s-1PS2\s+1\fP, \f3\s-1MAILCHECK\s+1\fP and \f3\s-1IFS\s+1\fP.
.SM
.B HOME
and
--- 548,554 -----
.RE
.PP
The shell gives default values to
! \f3\s-1HISTFILE\s+1\fP, \f3\s-1PATH\s+1\fP, \f3\s-1PS1\s+1\fP, \f3\s-1PS2\s+1\fP, \f3\s-1MAILCHECK\s+1\fP and \f3\s-1IFS\s+1\fP.
.SM
.B HOME
and
***************
*** 537,542
.B MAIL
are set by
.IR login (1).
.SS Blank Interpretation
After parameter and command substitution,
the results of substitution are scanned for internal field separator
--- 556,782 -----
.B MAIL
are set by
.IR login (1).
+ .SS Tilde Substitution
+ An unquoted tilde character
+ .RB ( ~ )
+ will cause the shell to attempt a tilde substituion. Tilde substitutions
+ are used to automatically determine home directories. Both the current
+ user's home directory, and the home directory of any other user on
+ the system may be found.
+ .PP
+ A
+ .B ~
+ by itself is equivalent to using
+ .BR \s-1$HOME\s+1 .
+ E.g.
+ .B ~/bin
+ is the same as saying
+ .BR \s-1$HOME\s+1/bin .
+ The notation
+ .B ~person
+ will cause the shell to look up
+ .BR person 's
+ home directory in the
+ .B /etc/passwd
+ file, and substitute it in. For example, if user
+ .BR arnold 's
+ home directory is
+ .BR /user/arnold ,
+ the shell would replace
+ .BR ~arnold/bin
+ with
+ .BR /user/arnold/bin .
+ .PP
+ Tilde substitutions are recognized at the beginning of words, after
+ equal signs (for shell variable assignment), in the middle of single letter
+ flag arguments to commands (e.g. \fBecho \-t~arnold\fP), and after
+ colons inside the
+ .B
+ .SM PATH
+ and
+ .B
+ .SM CDPATH
+ shell parameters.
+ .PP
+ If
+ .B /etc/passwd
+ cannot be read, or if
+ no user can be found to match the attempted tilde substitution,
+ the text is left unmodified.
+ .SS History Substitution
+ When reading input from an interactive terminal, a
+ .RB `` ! ''
+ character, anywhere on the line,
+ signals the shell that it should attempt
+ to perform a history substitution.
+ A history substitution is a shorthand method which allows the user
+ to recall all or part of a previous command, possibly editing the
+ recalled portion.
+ The recalled (and possibly changed) command line is then placed into
+ the current command line,
+ to be passed on to the rest of the shell for normal processing.
+ A history substitution takes the form:
+ .PP
+ .if t .RS
+ \fB!\fP\^[ \fIstr\fP | \fB?\fIstr\fB?\fR | \fInum\fP ]\c
+ [ \fB\(ga\fInum\fR [ \- [ \fInum\fP ] ]\c
+ { \fB^\fIstr\fB^\fIstr\fB^\fR [\fBg\fP] }
+ .if t .RE
+ .PP
+ A history substitution contains three parts;
+ command selection, argument selection, and editing.
+ .I Command selection
+ chooses what command will be retrieved from the stored
+ history.
+ .I Argument selection
+ chooses which arguments from that command will be extracted.
+ .I Editing
+ allows the user to change spelling or make a substitution.
+ .PP
+ The history substitution is triggered by the
+ .RB `` ! '',
+ and continues until another
+ .RB `` ! ''
+ is encountered, or until
+ something that could not be part of a history substitution is seen.
+ This is so that the
+ history substitution will be properly concatenated with the following text.
+ Whenever a history substitution is encountered and properly performed,
+ the shell echoes the resulting line to the terminal and then executes the
+ command.
+ .PP
+ History substitution occurs inside double quotes and grave accents, but will
+ not occur inside single quotes. To get a literal
+ .RB `` ! ''
+ character, outside of single quotes, precede it with a
+ .BR \e .
+ The
+ .BR ? ,
+ .BR \(ga ,
+ and
+ .B ^
+ characters are treated specially by the history mechanism only when preceded
+ by a
+ .RB `` ! '',
+ otherwise they have their normal meaning
+ of ``match a single character'',
+ ``enclose a command substitution'',
+ and as a synonym for the \fB\(bv\fP
+ character.
+ .PP
+ The full meaning of the history syntax is as follows:
+ .RS
+ .TP
+ \fB!\fP\^[ \fIstr\fP | \fB?\fIstr\fB?\fR | \fInum\fP ]
+ The first thing in a history substitution is
+ .IR "command selection" .
+ This is used to retrieve a given command line for use, or for further
+ processing. In a history command selection, \fB!\fIstr\fR
+ will find the most recent command line that started with the
+ characters in
+ .IR str .
+ \fB!?\fIstr\fB?\fR will find the most recent command line that contained
+ .I str
+ anywhere on the line. It also allows
+ .I str
+ to contain blanks and tabs, whereas the first form does not.
+ \fB!\fInum\fR allows the user to specify the number of a command, according
+ to the output of the
+ .B history
+ command (see the section on special commands, below).
+ .TP
+ \fB\(ga\fInum\fR [ \- [ \fInum\fP ]
+ The next portion of a history substitution is an optional
+ .IR "argument selection" .
+ This chooses which portions of the command are to be kept.
+ History arguments are not exactly the same as the arguments the rest of
+ the shell uses, since history expansion occurs before argument collection.
+ Arguments in this context are blank or tab separated words on the command line.
+ Single or double quoted strings, strings inside grave accents, shell regular
+ expressions, commands in parentheses (which get executed in a subshell),
+ and commands enclosed in braces,
+ are all treated as single arguments for the history mechanism, even though
+ they may have white space in them.
+ .sp
+ Arguments are numbered from zero, starting at the leftmost portion of the
+ line. In an argument selection, \fB\(ga\fInum\fR specifies that only argument
+ .I num
+ is to be extracted and kept for further processing or use, and the rest
+ of the command line is to be dropped.
+ \fB\(ga\fInum\fB\-\fInum\fR
+ specifies that the arguments from the first
+ .I num
+ to the last
+ .I num
+ are to be kept. In place of any
+ .IR num ,
+ .B $
+ may be specified to obtain the last argument on the line.
+ The form \fB\(ga\-\fInum\fR is a shorthand for \fB\(ga\fP1\fB\-\fInum\fR
+ and
+ \fB\(ga\fInum\fB\-\fR
+ is a short form for
+ \fB\(ga\fInum\fB\-$\fR.
+ Finally, the notation
+ \fB\(ga\-\fP
+ indicates all the arguments. That is, \fB\(ga\-\fP implies
+ \fB\(ga1\-$\fP.
+ .TP
+ \fB^\fIstr\fB^\fIstr\fB^\fR [\fBg\fP]
+ The last portion of a history substitution is also optional, and is the
+ .I editing
+ phase. This allows the remaining portions of the retrieved
+ command line to modified, like the substitute command in
+ .IR ed (1),
+ although in a much more limited fashion.
+ In the history mechanism,
+ .I str
+ is not a regular expression, as in
+ .IR ed,
+ but just a simple string.
+ The history mechanism does not recognize
+ either the shell's pattern matching characters or the editor's
+ regular expression characters.
+ Each substitution happens only once on a line, unless a trailing ``g''
+ is appended to the substitution. In this case, the substitution occurs
+ globally (everywhere) on the line.
+ Substitutions may be strung together,
+ so that more than one can be done at once.
+ The trailing ``g'' may be in either upper or lower case.
+ .RE
+ .PP
+ Some examples of history substitution are given below.
+ Should a history substitution fail, the errant command will
+ .I not
+ be added to the history buffers.
+ .PP
+ The history mechanism recognizes lines that end with unbalanced quotes.
+ When the quotes are balanced on the next line(s),
+ It will join this line with the one that opened the quotes, keeping the
+ embedded newline(s). So, e.g.,
+ .RS
+ .sp
+ .nf
+ .RB "$ " "echo 'open"
+ .RB "> " "close'"
+ .fi
+ .RE
+ .sp
+ will be saved as one history ``event.''
+ This does
+ .I not
+ extend to other shell constructs, like balancing parentheses across
+ newlines.
+ .PP
+ The history mechanism keeps a maximum of
+ 256
+ stored commands at any one time, and the total text of the
+ stored history may occupy no more than
+ 4096
+ characters.
+ Experience indicates that it is not necessary to store more than this,
+ and the extra history buffers should not make the shell too large for
+ machines with small address spaces (e.g. PDP-11's).
.SS Blank Interpretation
After history, tilde, parameter and command substitution,
the results of substitution are scanned for internal field separator
***************
*** 538,544
are set by
.IR login (1).
.SS Blank Interpretation
! After parameter and command substitution,
the results of substitution are scanned for internal field separator
characters (those found in
.BR \s-1IFS\s+1 )
--- 778,784 -----
and the extra history buffers should not make the shell too large for
machines with small address spaces (e.g. PDP-11's).
.SS Blank Interpretation
! After history, tilde, parameter and command substitution,
the results of substitution are scanned for internal field separator
characters (those found in
.BR \s-1IFS\s+1 )
***************
*** 593,598
is a
.RB `` ! ''
any character not enclosed is matched.
.PD
.RE
.SS Quoting
--- 833,843 -----
is a
.RB `` ! ''
any character not enclosed is matched.
+ Note that when typing input from the terminal, the
+ .RB `` ! ''
+ should be preceded by a
+ .BR \e ,
+ so that the shell does not attempt to perform a history substitution.
.PD
.RE
.SS Quoting
***************
*** 617,623
are quoted.
Inside double quote marks
(\f3"\^"\fP),
! parameter and command substitution occurs and
.B \e
quotes the characters
.BR \e ,
--- 862,868 -----
are quoted.
Inside double quote marks
(\f3"\^"\fP),
! history, parameter, and command substitution occurs and
.B \e
quotes the characters
.BR \e ,
***************
*** 623,628
.BR \e ,
.BR \*` ,
\f3"\fP,
and
.BR $ .
.B
--- 868,874 -----
.BR \e ,
.BR \*` ,
\f3"\fP,
+ .BR ! ,
and
.BR $ .
.B
***************
*** 660,665
(i.e., the value of
.BR \s-1PS2\s+1 )
is issued.
.SS Input/Output
Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
--- 906,971 -----
(i.e., the value of
.BR \s-1PS2\s+1 )
is issued.
+ .PP
+ Many people like to have the shell provide them with useful information
+ in their prompt. To accomadate this, the shell will recognize special
+ sequences of characters in the value of
+ .BR PS1 ,
+ and substitute the appropriate information for them.
+ The special sequences and what they signify are:
+ .RS
+ .TP
+ .B %d
+ Place the current working directory into the prompt.
+ .TP
+ .B %e
+ Place the current event number (as defined by the
+ .B history
+ command) into the prompt.
+ If history evaluation has been turned off (via
+ .BR "set -H" ),
+ no number will be substituted in (i.e. the
+ .B %e
+ will be removed).
+ .TP
+ .B %h
+ Place the machine's host name into the prompt. The host name is usually
+ the name by which the machine is known to the outside world for electronic
+ mail addressing.
+ .ig
+ At Georgia Tech, a leading ``gt'' or ``gt-'' in the host name will be removed.
+ ..
+ .TP
+ .B %l
+ Place the user's login name into the prompt.
+ The login name selected is the first entry in the
+ .B /etc/passwd
+ file whose
+ .I uid
+ matches the value of the
+ .IR getuid (2)
+ system call.
+ This will be a problem on systems where multiple users share the same
+ user-id number.
+ .TP
+ .B %t
+ Place the current time of day, in the form \s-1HH:MM\s+1 into the prompt.
+ The time is on a 24 hour clock, i.e. 1:30 in the afternoon will be 13:30.
+ .TP
+ .BI % x
+ Place the character
+ .I x
+ into the prompt.
+ If the user wishes to put a literal
+ .B %
+ into the prompt, then
+ .B PS1
+ should have
+ .B %%
+ in it.
+ .RE
+ .PP
+ Some of these facilities are of more use than others.
.SS Input/Output
Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
***************
*** 725,730
all leading tabs are stripped from
.I word\^
and from the document.
.TP
.B <\h at -.1m@&digit
Use the file associated with file descriptor
--- 1031,1038 -----
all leading tabs are stripped from
.I word\^
and from the document.
+ History substitution is turned off
+ while processing the document.
.TP
.B <\h at -.1m@&digit
Use the file associated with file descriptor
***************
*** 737,742
The standard input is closed.
Similarly for the standard output using
.BR >\h at -.1m@&\h at -.1m@\- .
.PD
.PP
If any of the above is preceded by a digit,
--- 1045,1058 -----
The standard input is closed.
Similarly for the standard output using
.BR >\h at -.1m@&\h at -.1m@\- .
+ .TP
+ .B <\&>\&word
+ Use file
+ .I word
+ for standard input (file descriptor 0),
+ but open it for reading
+ .I and
+ writing.
.PD
.PP
If any of the above is preceded by a digit,
***************
*** 806,812
.BR "set -a" ).
A parameter may be removed from the environment
with the
! .BR unset command.
The environment seen by any executed command is thus composed
of any unmodified name-value pairs originally inherited by the shell,
minus any pairs removed by
--- 1122,1129 -----
.BR "set -a" ).
A parameter may be removed from the environment
with the
! .B unset
! command.
The environment seen by any executed command is thus composed
of any unmodified name-value pairs originally inherited by the shell,
minus any pairs removed by
***************
*** 823,829
Thus:
.RS
.PP
! \s-1TERM\s+1=450 \|cmd and
.br
(export \|\s-1TERM\s+1; \|\s-1TERM\s+1=450; \|cmd)
.RE
--- 1140,1146 -----
Thus:
.RS
.PP
! \s-1TERM\s+1=450 \|cmd and
.br
(export \|\s-1TERM\s+1; \|\s-1TERM\s+1=450; \|cmd)
.RE
***************
*** 1083,1088
adjacent to the \f2hits\fR information.
\f2Cost\fR will be incremented when the recalculation is done.
.TP
\f3login\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Equivalent to
.BI "exec login" " arg\^"
--- 1400,1448 -----
adjacent to the \f2hits\fR information.
\f2Cost\fR will be incremented when the recalculation is done.
.TP
+ \fBhistory\fP \*(OK \fB\-irs\fP \*(OK \fIfilename\fP \*(CK \*(CK
+ The \fBhistory\fP command, with no arguments, will print all the commands that
+ are currently saved in the shell's history buffers. As new commands are
+ executed, and space in the buffers runs out, old commands will be deleted. The
+ .B history
+ commands prints out the stored commands with sequence numbers. Negative
+ numbered commands, through command number zero, are commands that were
+ retrieved from the saved history file. Commands starting at one were
+ entered during the current login session.
+ If a saved command contains embedded newlines, these will be printed out
+ as the sequence
+ .BR \en ,
+ so that individual command stay on one line.
+ .sp
+ The \fBhistory\fP command takes two optional arguments. If the first
+ argument is \fB\-s\fP, the shell will save its current history buffers
+ in the file named as the third argument. If no file is given, it will
+ use the value of
+ .BR \s-1HISTFILE\s+1 .
+ .sp
+ Similarly, if the first argument is \fB\-r\fP, the shell will reset its
+ history buffers from the saved history in the file given as the third argument.
+ Again, if no file name is given,
+ .B \s-1$HISTFILE\s+1
+ will be used.
+ .sp
+ The command
+ .B history -i
+ will cause the shell to reinitialize its history buffers. In other words,
+ all the shell's saved history will be thrown away, and the shell will
+ start from scratch.
+ .sp
+ The \fBhistory\fP command will have absolutely no effect at all if input
+ is not coming from a terminal. I.e., inside shell files, the
+ .B history
+ command is effectively a null operation.
+ .sp
+ The
+ .B history
+ command will always have an exit status of 1 inside a shell file.
+ If input is coming from a terminal, then the exit status wil be 0
+ if the command succeeds, 1 otherwise.
+ .TP
\f3login\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Equivalent to
.BI "exec login" " arg\^"
***************
*** 1136,1142
.I n
is omitted, the return status is that of the last command executed.
.TP
! \f3set\fP \*(OK \f3\-\-aefhkntuvxEIJ\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK \*(CK
.RS
.TP
.B \-a
--- 1496,1502 -----
.I n
is omitted, the return status is that of the last command executed.
.TP
! \f3set\fP \*(OK \f3\-\-aefhkntuvxEHIJ\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK \*(CK
.RS
.TP
.B \-a
***************
*** 1180,1185
.IR .profile\^ s
to avoid accidental logout.
.TP
.B \-I
(BRL addition)
Prints a resource usage summary
--- 1540,1562 -----
.IR .profile\^ s
to avoid accidental logout.
.TP
+ .B \-H
+ Disable history processing. If the shell is invoked with this option,
+ it will not bother trying to restore its saved history from the
+ contents of
+ .BR \s-1$HISTFILE\s+1 .
+ While this flag is in effect, the shell will not save any commands in
+ its history buffers.
+ The sequence
+ .B %e
+ in the value of
+ .B \s-1PS1\s+1
+ will also have no effect on the generated prompt string.
+ If
+ .B set +H
+ is used to turn history processing back on, the shell will start saving
+ subsequent commands from that point on.
+ .TP
.B \-I
(BRL addition)
Prints a resource usage summary
***************
*** 1332,1337
and from
.BR \s-1$HOME\s+1/.profile ,
if such files exist.
Thereafter, commands are read as described below, which
is also the case when the shell is invoked as
.BR /bin/sh .
--- 1709,1726 -----
and from
.BR \s-1$HOME\s+1/.profile ,
if such files exist.
+ Next, whether or not the first character of argument zero was a
+ .BR \- ,
+ and no matter how the shell was invoked,
+ the shell will read commands from the file
+ .BR \s-1$HOME\s+1/.shrc ,
+ if it exists.
+ Then, if the shell is interactive, is not a forked subshell,
+ and the
+ .B \-H
+ flag is not in effect,
+ it will attempt to restore its saved history from
+ .BR \s-1$HISTFILE\s+1 .
Thereafter, commands are read as described below, which
is also the case when the shell is invoked as
.BR /bin/sh .
***************
*** 1340,1345
the
.B \-J
(job control) flag is automatically set.
The flags below are interpreted by the shell on invocation only; note
that unless the
.B \-c
--- 1729,1740 -----
the
.B \-J
(job control) flag is automatically set.
+ .ig
+ At Georgia Tech, job control is always turned on, even if the
+ .B \-J
+ flag was not given, and even if argument zero did not contain a
+ .BR j .
+ ..
The flags below are interpreted by the shell on invocation only; note
that unless the
.B \-c
***************
*** 1388,1393
If the
.B \-r
flag is present the shell is a restricted shell.
.PD
.PP
The remaining flags and arguments are described under the
--- 1783,1799 -----
If the
.B \-r
flag is present the shell is a restricted shell.
+ .TP
+ .B \-q
+ If the
+ .B \-q
+ flag is present, the shell will do a ``quick'' startup.
+ This means that the shell will
+ .I not
+ read the contents of the
+ .B \s-1$HOME\s+1/.shrc
+ file.
+ The shell will also not try to read this file if it is a restricted shell.
.PD
.PP
The remaining flags and arguments are described under the
***************
*** 1425,1430
If the process group
.I n\^
is not specified then the ``current job'' is resumed.
.PD
.PP
With job control enabled,
--- 1831,1842 -----
If the process group
.I n\^
is not specified then the ``current job'' is resumed.
+ .TP
+ .B suspend
+ Suspend the shell process itself in the background.
+ The shell will complain
+ if it is a login shell, and will not suspend itself.
+ Otherwise, it does not matter whether or not job control is enabled.
.PD
.PP
With job control enabled,
***************
*** 1441,1446
If the specified job number is one of the known jobs,
then this expression is replaced by
the corresponding process group number.
.PD
.SH EXIT STATUS
Errors detected by the shell, such as syntax errors,
--- 1853,1886 -----
If the specified job number is one of the known jobs,
then this expression is replaced by
the corresponding process group number.
+ .SS Saving and Restoring History
+ When an interactive shell starts up, if the
+ .B \-H
+ flag is not in effect, it will attempt to read the contents of
+ .B \s-1$HISTFILE\s+1
+ into its history buffers. This allows the user to recall commands
+ executed during a previous login session.
+ When the shell exits or executes an
+ .B exec
+ (again, if
+ .B \-H
+ is not in effect), it will attempt to write its current history
+ buffers into
+ .BR \s-1$HISTFILE\s+1 ,
+ for use in a future login session.
+ .PP
+ The
+ .B history
+ command allows the user to save the current history buffers into
+ a file of his or her own choosing, or to restore them from a given file.
+ If
+ .B \-H
+ has been set, the
+ .B history
+ command will give a warning that history processing is not
+ available, and will
+ .I not
+ save or restore the shell's history buffers.
.PD
.SH EXIT STATUS
Errors detected by the shell, such as syntax errors,
***************
*** 1457,1462
.br
\s-1$HOME\s+1/\f3.\fPprofile
.br
/tmp/sh\(**
.br
/dev/null
--- 1897,1904 -----
.br
\s-1$HOME\s+1/\f3.\fPprofile
.br
+ \s-1$HOME\s+1/\f3.\fPshrc
+ .br
/tmp/sh\(**
.br
/dev/null
***************
*** 1464,1469
acctcom(1),
cd(1),
echo(1),
env(1),
login(1),
newgrp(1),
--- 1906,1912 -----
acctcom(1),
cd(1),
echo(1),
+ ed(1),
env(1),
login(1),
newgrp(1),
***************
*** 1477,1482
dup(2),
exec(2),
fork(2),
pipe(2),
signal(2),
ulimit(2),
--- 1920,1927 -----
dup(2),
exec(2),
fork(2),
+ getppid(2),
+ getuid(2),
pipe(2),
signal(2),
ulimit(2),
***************
*** 1510,1512
.B login
command is replaced by
.BR newgrp .
--- 1955,2071 -----
.B login
command is replaced by
.BR newgrp .
+ .SH PYRAMID SPECIFIC
+ .PP
+ On computers manufactured by the Pyramid Corporation, which support
+ both the University of California at Berkeley 4.2BSD version of \s-1UNIX\s+1,
+ and the AT&T System V version of \s-1UNIX\s+1,
+ the shell has several additional capabilities.
+ .SS Special Commands
+ .PP
+ There are three additional commands built in to the shell. They are:
+ .RS
+ .TP
+ \fBatt\fP \*(OK command \*(CK
+ Switch the current ``universe'' to be ATT System V.
+ If a command is specified, that command will be run in the ``att''
+ universe, without affecting the shell's current universe.
+ The
+ .B \-t
+ option of
+ .B /bin/att
+ is not (yet) supported.
+ .TP
+ \fBucb\fP \*(OK command \*(CK
+ Switch the current ``universe'' to be University of California at
+ Berkeley 4.2BSD.
+ If a command is specified, that command will be run in the ``ucb''
+ universe, without affecting the shell's current universe.
+ The
+ .B \-t
+ option of
+ .B /bin/ucb
+ is not (yet) supported.
+ .TP
+ \fBuniverse\fP \*(OK \fB\-l\fP \*(CK
+ Print the current universe, either ``att'' or ``ucb''. The
+ .B \-l
+ option will print a longer, more explanative name for the current universe.
+ .RE
+ .PP
+ If the shell cannot determine the current universe when it starts up,
+ it will default to
+ .BR ucb .
+ .SS Shell Variables
+ .PP
+ There is an additional pre-defined shell parameter,
+ .BR \s-1UNIVERSE\s+1 .
+ The value of
+ .B \s-1UNIVERSE\s+1
+ .I always
+ tracks that of the current universe. Using it is equivalent to a
+ \*`universe\` command substitution,
+ except that a new process will not be created.
+ This variable cannot be set by the user (it is \fBreadonly\fP),
+ and any inherited value from the environment will be ignored.
+ .SS Special Sequences for \s-1PS1\s+1
+ .PP
+ Finally, the sequence
+ .B %u
+ in the value of
+ .B \s-1PS1\s-1
+ will cause the shell to subsitute in the name of the current universe,
+ either ``att'' or ``ucb''.
+ .SH HISTORY EXAMPLES
+ Command history provides a powerful method for easily redoing previous
+ commands, or for quicly fixing typing mistakes.
+ Here are some annotated examples. User input is in
+ .BR boldface .
+ .sp
+ .nf
+ # first, list some files
+ .RB "$ " lf
+ hello.c echo.c
+ # now, make a typing mistake
+ .RB "$ " "cat hello"
+ hello: No such file or directory
+ # fix it. The trailing ! ends the history substitution,
+ # in order to correctly concatenate it with the following .c
+ .RB "$ " "!!.c"
+ cat hello.c
+ main () { printf ("hello world\en"); }
+ # now look at echo.c instead
+ .RB "$ " "!^hello^echo"
+ cat echo.c
+ main () { printf ("echo: no arguments\en"); }
+ # do it again, just for fun
+ .RB "$ " "!"
+ cat echo.c
+ main () { printf ("echo: no arguments\en"); }
+ # now we'll rearrange some arguments
+ .RB "$ " "echo 1 2 3 4 5"
+ 1 2 3 4 5
+ # print last argument, first and second arguments, then change 4 to four
+ .RB "$ " "echo !\(ga$ !\(ga1-2 !\(ga4^4^four"
+ echo 5 1 2 four
+ 5 1 2 four
+ # do something with all the previous arguments at once
+ .RB "$ " "echo the previous arguments were !\(ga\-"
+ echo the previous arguments were 5 1 2 four
+ the previous arguments were 5 1 2 four
+ # now do some substitutions. first get something to work with.
+ .RB "$ " "echo aa bb cc"
+ aa bb cc
+ # change the first 'a' to a 'b', and change all c's to d's
+ .RB "$ " "!^a^b^^c^d^g"
+ echo ba bb dd
+ ba bb dd
+ .fi
+ .PP
+ These few brief examples should provide a general feel for the
+ history mechanism. The quickest way to learn it is to experiment
+ with it for a while, using the
+ .B echo
+ command, which can do very little damage.
+ While it looks cryptic when being typed, it is very general and
+ orthogonal, and quickly becomes natural.
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