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mycroft
parent
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# @(#)Makefile 8.1 (Berkeley) 8/14/93
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DIR= usd/04.csh
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SRCS= tabs csh.1 csh.2 csh.3 csh.4 csh.a csh.g
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MACROS= -ms
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.include <bsd.doc.mk>
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File diff suppressed because it is too large
Load Diff
File diff suppressed because it is too large
Load Diff
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@ -0,0 +1,650 @@
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.\" Copyright (c) 1980, 1993
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.\" The Regents of the University of California. All rights reserved.
|
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.\"
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.\" 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. All advertising materials mentioning features or use of this software
|
||||
.\" must display the following acknowledgement:
|
||||
.\" This product includes software developed by the University of
|
||||
.\" California, Berkeley and its contributors.
|
||||
.\" 4. Neither the name of the University nor the names of its contributors
|
||||
.\" 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.
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.\"
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.\" @(#)csh.3 8.1 (Berkeley) 6/8/93
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.\"
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.nr H1 2
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.NH
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Shell control structures and command scripts
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.NH 2
|
||||
Introduction
|
||||
.PP
|
||||
It is possible to place commands in files and to cause shells to be
|
||||
invoked to read and execute commands from these files,
|
||||
which are called
|
||||
.I "shell scripts."
|
||||
We here detail those features of the shell useful to the writers of such
|
||||
scripts.
|
||||
.NH 2
|
||||
Make
|
||||
.PP
|
||||
It is important to first note what shell scripts are
|
||||
.I not
|
||||
useful for.
|
||||
There is a program called
|
||||
.I make
|
||||
which is very useful for maintaining a group of related files
|
||||
or performing sets of operations on related files.
|
||||
For instance a large program consisting of one or more files
|
||||
can have its dependencies described in a
|
||||
.I makefile
|
||||
which contains definitions of the commands used to create these
|
||||
different files when changes occur.
|
||||
Definitions of the means for printing listings, cleaning up the directory
|
||||
in which the files reside, and installing the resultant programs
|
||||
are easily, and most appropriately placed in this
|
||||
.I makefile.
|
||||
This format is superior and preferable to maintaining a group of shell
|
||||
procedures to maintain these files.
|
||||
.PP
|
||||
Similarly when working on a document a
|
||||
.I makefile
|
||||
may be created which defines how different versions of the document
|
||||
are to be created and which options of
|
||||
.I nroff
|
||||
or
|
||||
.I troff
|
||||
are appropriate.
|
||||
.NH 2
|
||||
Invocation and the argv variable
|
||||
.PP
|
||||
A
|
||||
.I csh
|
||||
command script may be interpreted by saying
|
||||
.DS
|
||||
% csh script ...
|
||||
.DE
|
||||
where
|
||||
.I script
|
||||
is the name of the file containing a group of
|
||||
.I csh
|
||||
commands and
|
||||
`\&...' is replaced by a sequence of arguments.
|
||||
The shell places these arguments in the variable
|
||||
.I argv
|
||||
and then begins to read commands from the script.
|
||||
These parameters are then available through the same mechanisms
|
||||
which are used to reference any other shell variables.
|
||||
.PP
|
||||
If you make the file
|
||||
`script'
|
||||
executable by doing
|
||||
.DS
|
||||
chmod 755 script
|
||||
.DE
|
||||
and place a shell comment at the beginning of the shell script
|
||||
(i.e. begin the file with a `#' character)
|
||||
then a `/bin/csh' will automatically be invoked to execute `script' when
|
||||
you type
|
||||
.DS
|
||||
script
|
||||
.DE
|
||||
If the file does not begin with a `#' then the standard shell
|
||||
`/bin/sh' will be used to execute it.
|
||||
This allows you to convert your older shell scripts to use
|
||||
.I csh
|
||||
at your convenience.
|
||||
.NH 2
|
||||
Variable substitution
|
||||
.PP
|
||||
After each input line is broken into words and history substitutions
|
||||
are done on it, the input line is parsed into distinct commands.
|
||||
Before each command is executed a mechanism know as
|
||||
.I "variable substitution"
|
||||
is done on these words.
|
||||
Keyed by the character `$' this substitution replaces the names
|
||||
of variables by their values.
|
||||
Thus
|
||||
.DS
|
||||
echo $argv
|
||||
.DE
|
||||
when placed in a command script would cause the current value of the
|
||||
variable
|
||||
.I argv
|
||||
to be echoed to the output of the shell script.
|
||||
It is an error for
|
||||
.I argv
|
||||
to be unset at this point.
|
||||
.PP
|
||||
A number of notations are provided for accessing components and attributes
|
||||
of variables.
|
||||
The notation
|
||||
.DS
|
||||
$?name
|
||||
.DE
|
||||
expands to `1' if name is
|
||||
.I set
|
||||
or to `0'
|
||||
if name is not
|
||||
.I set.
|
||||
It is the fundamental mechanism used for checking whether particular
|
||||
variables have been assigned values.
|
||||
All other forms of reference to undefined variables cause errors.
|
||||
.PP
|
||||
The notation
|
||||
.DS
|
||||
$#name
|
||||
.DE
|
||||
expands to the number of elements in the variable
|
||||
.I name.
|
||||
Thus
|
||||
.DS
|
||||
% set argv=(a b c)
|
||||
% echo $?argv
|
||||
1
|
||||
% echo $#argv
|
||||
3
|
||||
% unset argv
|
||||
% echo $?argv
|
||||
0
|
||||
% echo $argv
|
||||
Undefined variable: argv.
|
||||
%
|
||||
.DE
|
||||
.PP
|
||||
It is also possible to access the components of a variable
|
||||
which has several values.
|
||||
Thus
|
||||
.DS
|
||||
$argv[1]
|
||||
.DE
|
||||
gives the first component of
|
||||
.I argv
|
||||
or in the example above `a'.
|
||||
Similarly
|
||||
.DS
|
||||
$argv[$#argv]
|
||||
.DE
|
||||
would give `c',
|
||||
and
|
||||
.DS
|
||||
$argv[1\-2]
|
||||
.DE
|
||||
would give `a b'. Other notations useful in shell scripts are
|
||||
.DS
|
||||
$\fIn\fR
|
||||
.DE
|
||||
where
|
||||
.I n
|
||||
is an integer as a shorthand for
|
||||
.DS
|
||||
$argv[\fIn\fR\|]
|
||||
.DE
|
||||
the
|
||||
.I n\|th
|
||||
parameter and
|
||||
.DS
|
||||
$*
|
||||
.DE
|
||||
which is a shorthand for
|
||||
.DS
|
||||
$argv
|
||||
.DE
|
||||
The form
|
||||
.DS
|
||||
$$
|
||||
.DE
|
||||
expands to the process number of the current shell.
|
||||
Since this process number is unique in the system it can
|
||||
be used in generation of unique temporary file names.
|
||||
The form
|
||||
.DS
|
||||
$<
|
||||
.DE
|
||||
is quite special and is replaced by the next line of input read from
|
||||
the shell's standard input (not the script it is reading). This is
|
||||
useful for writing shell scripts that are interactive, reading
|
||||
commands from the terminal, or even writing a shell script that
|
||||
acts as a filter, reading lines from its input file. Thus the sequence
|
||||
.DS
|
||||
echo 'yes or no?\ec'
|
||||
set a=($<)
|
||||
.DE
|
||||
would write out the prompt `yes or no?' without a newline and then
|
||||
read the answer into the variable `a'. In this case `$#a' would be
|
||||
`0' if either a blank line or end-of-file (^D) was typed.
|
||||
.PP
|
||||
One minor difference between `$\fIn\fR\|' and `$argv[\fIn\fR\|]'
|
||||
should be noted here.
|
||||
The form
|
||||
`$argv[\fIn\fR\|]'
|
||||
will yield an error if
|
||||
.I n
|
||||
is not in the range
|
||||
`1\-$#argv'
|
||||
while `$n'
|
||||
will never yield an out of range subscript error.
|
||||
This is for compatibility with the way older shells handled parameters.
|
||||
.PP
|
||||
Another important point is that it is never an error to give a subrange
|
||||
of the form `n\-'; if there are less than
|
||||
.I n
|
||||
components of the given variable then no words are substituted.
|
||||
A range of the form `m\-n' likewise returns an empty vector without giving
|
||||
an error when \fIm\fR exceeds the number of elements of the given variable,
|
||||
provided the subscript \fIn\fR is in range.
|
||||
.NH 2
|
||||
Expressions
|
||||
.PP
|
||||
In order for interesting shell scripts to be constructed it
|
||||
must be possible to evaluate expressions in the shell based on the
|
||||
values of variables.
|
||||
In fact, all the arithmetic operations of the language C are available
|
||||
in the shell
|
||||
with the same precedence that they have in C.
|
||||
In particular, the operations `==' and `!=' compare strings
|
||||
and the operators `&&' and `|\|\||' implement the boolean and/or operations.
|
||||
The special operators `=~' and `!~' are similar to `==' and `!=' except
|
||||
that the string on the right side can have pattern matching characters
|
||||
(like *, ? or []) and the test is whether the string on the left matches
|
||||
the pattern on the right.
|
||||
.PP
|
||||
The shell also allows file enquiries of the form
|
||||
.DS
|
||||
\-? filename
|
||||
.DE
|
||||
where `?' is replace by a number of single characters.
|
||||
For instance the expression primitive
|
||||
.DS
|
||||
\-e filename
|
||||
.DE
|
||||
tell whether the file
|
||||
`filename'
|
||||
exists.
|
||||
Other primitives test for read, write and execute access to the file,
|
||||
whether it is a directory, or has non-zero length.
|
||||
.PP
|
||||
It is possible to test whether a command terminates normally,
|
||||
by a primitive of the
|
||||
form `{ command }' which returns true, i.e. `1' if the command
|
||||
succeeds exiting normally with exit status 0, or `0' if the command
|
||||
terminates abnormally or with exit status non-zero.
|
||||
If more detailed information about the execution status of a command
|
||||
is required, it can be executed and the variable `$status' examined
|
||||
in the next command.
|
||||
Since `$status' is set by every command, it is very transient.
|
||||
It can be saved if it is inconvenient to use it only in the single
|
||||
immediately following command.
|
||||
.PP
|
||||
For a full list of expression components available see the manual
|
||||
section for the shell.
|
||||
.NH 2
|
||||
Sample shell script
|
||||
.PP
|
||||
A sample shell script which makes use of the expression mechanism
|
||||
of the shell and some of its control structure follows:
|
||||
.DS
|
||||
% cat copyc
|
||||
#
|
||||
# Copyc copies those C programs in the specified list
|
||||
# to the directory ~/backup if they differ from the files
|
||||
# already in ~/backup
|
||||
#
|
||||
set noglob
|
||||
foreach i ($argv)
|
||||
|
||||
if ($i !~ *.c) continue # not a .c file so do nothing
|
||||
|
||||
if (! \-r ~/backup/$i:t) then
|
||||
echo $i:t not in backup... not cp\e\'ed
|
||||
continue
|
||||
endif
|
||||
|
||||
cmp \-s $i ~/backup/$i:t # to set $status
|
||||
|
||||
if ($status != 0) then
|
||||
echo new backup of $i
|
||||
cp $i ~/backup/$i:t
|
||||
endif
|
||||
end
|
||||
.DE
|
||||
.PP
|
||||
This script makes use of the
|
||||
.I foreach
|
||||
command, which causes the shell to execute the commands between the
|
||||
.I foreach
|
||||
and the matching
|
||||
.I end
|
||||
for each of the values given between `(' and `)' with the named
|
||||
variable, in this case `i' set to successive values in the list.
|
||||
Within this loop we may use the command
|
||||
.I break
|
||||
to stop executing the loop
|
||||
and
|
||||
.I continue
|
||||
to prematurely terminate one iteration
|
||||
and begin the next.
|
||||
After the
|
||||
.I foreach
|
||||
loop the iteration variable
|
||||
(\fIi\fR in this case)
|
||||
has the value at the last iteration.
|
||||
.PP
|
||||
We set the variable
|
||||
.I noglob
|
||||
here to prevent filename expansion of the members of
|
||||
.I argv.
|
||||
This is a good idea, in general, if the arguments to a shell script
|
||||
are filenames which have already been expanded or if the arguments
|
||||
may contain filename expansion metacharacters.
|
||||
It is also possible to quote each use of a `$' variable expansion,
|
||||
but this is harder and less reliable.
|
||||
.PP
|
||||
The other control construct used here is a statement of the form
|
||||
.DS
|
||||
\fBif\fR ( expression ) \fBthen\fR
|
||||
command
|
||||
...
|
||||
\fBendif\fR
|
||||
.DE
|
||||
The placement of the keywords here is
|
||||
.B not
|
||||
flexible due to the current implementation of the shell.\(dg
|
||||
.FS
|
||||
\(dgThe following two formats are not currently acceptable to the shell:
|
||||
.sp
|
||||
.in +5
|
||||
.nf
|
||||
\fBif\fR ( expression ) # \fBWon't work!\fR
|
||||
\fBthen\fR
|
||||
command
|
||||
...
|
||||
\fBendif\fR
|
||||
.fi
|
||||
.in -5
|
||||
.sp
|
||||
and
|
||||
.sp
|
||||
.in +5
|
||||
.nf
|
||||
\fBif\fR ( expression ) \fBthen\fR command \fBendif\fR # \fBWon't work\fR
|
||||
.in -5
|
||||
.fi
|
||||
.FE
|
||||
.PP
|
||||
The shell does have another form of the if statement of the form
|
||||
.DS
|
||||
\fBif\fR ( expression ) \fBcommand\fR
|
||||
.DE
|
||||
which can be written
|
||||
.DS
|
||||
\fBif\fR ( expression ) \e
|
||||
command
|
||||
.DE
|
||||
Here we have escaped the newline for the sake of appearance.
|
||||
The command must not involve `\||\|', `&' or `;'
|
||||
and must not be another control command.
|
||||
The second form requires the final `\e' to
|
||||
.B immediately
|
||||
precede the end-of-line.
|
||||
.PP
|
||||
The more general
|
||||
.I if
|
||||
statements above also admit a sequence of
|
||||
.I else\-if
|
||||
pairs followed by a single
|
||||
.I else
|
||||
and an
|
||||
.I endif,
|
||||
e.g.:
|
||||
.DS
|
||||
\fBif\fR ( expression ) \fBthen\fR
|
||||
commands
|
||||
\fBelse\fR \fBif\fR (expression ) \fBthen\fR
|
||||
commands
|
||||
\&...
|
||||
|
||||
\fBelse\fR
|
||||
commands
|
||||
\fBendif\fR
|
||||
.DE
|
||||
.PP
|
||||
Another important mechanism used in shell scripts is the `:' modifier.
|
||||
We can use the modifier `:r' here to extract a root of a filename or
|
||||
`:e' to extract the
|
||||
.I extension.
|
||||
Thus if the variable
|
||||
.I i
|
||||
has the value
|
||||
`/mnt/foo.bar'
|
||||
then
|
||||
.sp
|
||||
.in +5
|
||||
.nf
|
||||
% echo $i $i:r $i:e
|
||||
/mnt/foo.bar /mnt/foo bar
|
||||
%
|
||||
.sp
|
||||
.in -5
|
||||
.fi
|
||||
shows how the `:r' modifier strips off the trailing `.bar' and the
|
||||
the `:e' modifier leaves only the `bar'.
|
||||
Other modifiers will take off the last component of a pathname leaving
|
||||
the head `:h' or all but the last component of a pathname leaving the
|
||||
tail `:t'.
|
||||
These modifiers are fully described in the
|
||||
.I csh
|
||||
manual pages in the User's Reference Manual.
|
||||
It is also possible to use the
|
||||
.I "command substitution"
|
||||
mechanism described in the next major section to perform modifications
|
||||
on strings to then reenter the shell's environment.
|
||||
Since each usage of this mechanism involves the creation of a new process,
|
||||
it is much more expensive to use than the `:' modification mechanism.\(dd
|
||||
.FS
|
||||
\(dd It is also important to note that
|
||||
the current implementation of the shell limits the number of `:' modifiers
|
||||
on a `$' substitution to 1.
|
||||
Thus
|
||||
.sp
|
||||
.nf
|
||||
.in +5
|
||||
% echo $i $i:h:t
|
||||
/a/b/c /a/b:t
|
||||
%
|
||||
.in -5
|
||||
.fi
|
||||
.sp
|
||||
does not do what one would expect.
|
||||
.FE
|
||||
Finally, we note that the character `#' lexically introduces a shell
|
||||
comment in shell scripts (but not from the terminal).
|
||||
All subsequent characters on the input line after a `#' are discarded
|
||||
by the shell.
|
||||
This character can be quoted using `\'' or `\e' to place it in
|
||||
an argument word.
|
||||
.NH 2
|
||||
Other control structures
|
||||
.PP
|
||||
The shell also has control structures
|
||||
.I while
|
||||
and
|
||||
.I switch
|
||||
similar to those of C.
|
||||
These take the forms
|
||||
.DS
|
||||
\fBwhile\fR ( expression )
|
||||
commands
|
||||
\fBend\fR
|
||||
.DE
|
||||
and
|
||||
.DS
|
||||
\fBswitch\fR ( word )
|
||||
|
||||
\fBcase\fR str1:
|
||||
commands
|
||||
\fBbreaksw\fR
|
||||
|
||||
\& ...
|
||||
|
||||
\fBcase\fR strn:
|
||||
commands
|
||||
\fBbreaksw\fR
|
||||
|
||||
\fBdefault:\fR
|
||||
commands
|
||||
\fBbreaksw\fR
|
||||
|
||||
\fBendsw\fR
|
||||
.DE
|
||||
For details see the manual section for
|
||||
.I csh.
|
||||
C programmers should note that we use
|
||||
.I breaksw
|
||||
to exit from a
|
||||
.I switch
|
||||
while
|
||||
.I break
|
||||
exits a
|
||||
.I while
|
||||
or
|
||||
.I foreach
|
||||
loop.
|
||||
A common mistake to make in
|
||||
.I csh
|
||||
scripts is to use
|
||||
.I break
|
||||
rather than
|
||||
.I breaksw
|
||||
in switches.
|
||||
.PP
|
||||
Finally,
|
||||
.I csh
|
||||
allows a
|
||||
.I goto
|
||||
statement, with labels looking like they do in C, i.e.:
|
||||
.DS
|
||||
loop:
|
||||
commands
|
||||
\fBgoto\fR loop
|
||||
.DE
|
||||
.NH 2
|
||||
Supplying input to commands
|
||||
.PP
|
||||
Commands run from shell scripts receive by default the standard
|
||||
input of the shell which is running the script.
|
||||
This is different from previous shells running
|
||||
under \s-2UNIX\s0. It allows shell scripts to fully participate
|
||||
in pipelines, but mandates extra notation for commands which are to take
|
||||
inline data.
|
||||
.PP
|
||||
Thus we need a metanotation for supplying inline data to commands in
|
||||
shell scripts.
|
||||
As an example, consider this script which runs the editor to
|
||||
delete leading blanks from the lines in each argument file:
|
||||
.DS
|
||||
% cat deblank
|
||||
# deblank \-\- remove leading blanks
|
||||
foreach i ($argv)
|
||||
ed \- $i << \'EOF\'
|
||||
1,$s/^[ ]*//
|
||||
w
|
||||
q
|
||||
\&\'EOF\'
|
||||
end
|
||||
%
|
||||
.DE
|
||||
The notation `<< \'EOF\''
|
||||
means that the standard input for the
|
||||
.I ed
|
||||
command is to come from the text in the shell script file
|
||||
up to the next line consisting of exactly `\'EOF\''.
|
||||
The fact that the `EOF' is enclosed in `\'' characters, i.e. quoted,
|
||||
causes the shell to not perform variable substitution on the
|
||||
intervening lines.
|
||||
In general, if any part of the word following the `<<' which the
|
||||
shell uses to terminate the text to be given to the command is quoted
|
||||
then these substitutions will not be performed.
|
||||
In this case since we used the form `1,$' in our editor script
|
||||
we needed to insure that this `$' was not variable substituted.
|
||||
We could also have insured this by preceding the `$' here with a `\e',
|
||||
i.e.:
|
||||
.DS
|
||||
1,\e$s/^[ ]*//
|
||||
.DE
|
||||
but quoting the `EOF' terminator is a more reliable way of achieving the
|
||||
same thing.
|
||||
.NH 2
|
||||
Catching interrupts
|
||||
.PP
|
||||
If our shell script creates temporary files, we may wish to catch
|
||||
interruptions of the shell script so that we can clean up
|
||||
these files.
|
||||
We can then do
|
||||
.DS
|
||||
onintr label
|
||||
.DE
|
||||
where
|
||||
.I label
|
||||
is a label in our program.
|
||||
If an interrupt is received the shell will do a
|
||||
`goto label'
|
||||
and we can remove the temporary files and then do an
|
||||
.I exit
|
||||
command (which is built in to the shell)
|
||||
to exit from the shell script.
|
||||
If we wish to exit with a non-zero status we can do
|
||||
.DS
|
||||
exit(1)
|
||||
.DE
|
||||
e.g. to exit with status `1'.
|
||||
.NH 2
|
||||
What else?
|
||||
.PP
|
||||
There are other features of the shell useful to writers of shell
|
||||
procedures.
|
||||
The
|
||||
.I verbose
|
||||
and
|
||||
.I echo
|
||||
options and the related
|
||||
.I \-v
|
||||
and
|
||||
.I \-x
|
||||
command line options can be used to help trace the actions of the shell.
|
||||
The
|
||||
.I \-n
|
||||
option causes the shell only to read commands and not to execute
|
||||
them and may sometimes be of use.
|
||||
.PP
|
||||
One other thing to note is that
|
||||
.I csh
|
||||
will not execute shell scripts which do not begin with the
|
||||
character `#', that is shell scripts that do not begin with a comment.
|
||||
Similarly, the `/bin/sh' on your system may well defer to `csh'
|
||||
to interpret shell scripts which begin with `#'.
|
||||
This allows shell scripts for both shells to live in harmony.
|
||||
.PP
|
||||
There is also another quotation mechanism using `"' which allows
|
||||
only some of the expansion mechanisms we have so far discussed to occur
|
||||
on the quoted string and serves to make this string into a single word
|
||||
as `\'' does.
|
||||
.bp
|
||||
|
|
@ -0,0 +1,178 @@
|
|||
.\" Copyright (c) 1980, 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. All advertising materials mentioning features or use of this software
|
||||
.\" must display the following acknowledgement:
|
||||
.\" This product includes software developed by the University of
|
||||
.\" California, Berkeley and its contributors.
|
||||
.\" 4. Neither the name of the University nor the names of its contributors
|
||||
.\" 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.
|
||||
.\"
|
||||
.\" @(#)csh.4 8.1 (Berkeley) 6/8/93
|
||||
.\"
|
||||
.nr H1 3
|
||||
.NH
|
||||
Other, less commonly used, shell features
|
||||
.NH 2
|
||||
Loops at the terminal; variables as vectors
|
||||
.PP
|
||||
It is occasionally useful to use the
|
||||
.I foreach
|
||||
control structure at the terminal to aid in performing a number
|
||||
of similar commands.
|
||||
For instance, there were at one point three shells in use on the Cory \s-2UNIX\s0
|
||||
system at Cory Hall,
|
||||
`/bin/sh',
|
||||
`/bin/nsh',
|
||||
and
|
||||
`/bin/csh'.
|
||||
To count the number of persons using each shell one could have issued
|
||||
the commands
|
||||
.DS
|
||||
% grep \-c csh$ /etc/passwd
|
||||
27
|
||||
% grep \-c nsh$ /etc/passwd
|
||||
128
|
||||
% grep \-c \-v sh$ /etc/passwd
|
||||
430
|
||||
%
|
||||
.DE
|
||||
Since these commands are very similar we can use
|
||||
.I foreach
|
||||
to do this more easily.
|
||||
.DS
|
||||
% foreach i (\'sh$\' \'csh$\' \'\-v sh$\')
|
||||
? grep \-c $i /etc/passwd
|
||||
? end
|
||||
27
|
||||
128
|
||||
430
|
||||
%
|
||||
.DE
|
||||
Note here that the shell prompts for
|
||||
input with `? ' when reading the body of the loop.
|
||||
.PP
|
||||
Very useful with loops are variables which contain lists of filenames
|
||||
or other words.
|
||||
You can, for example, do
|
||||
.DS
|
||||
% set a=(\`ls\`)
|
||||
% echo $a
|
||||
csh.n csh.rm
|
||||
% ls
|
||||
csh.n
|
||||
csh.rm
|
||||
% echo $#a
|
||||
2
|
||||
%
|
||||
.DE
|
||||
The
|
||||
.I set
|
||||
command here gave the variable
|
||||
.I a
|
||||
a list of all the filenames in the current directory as value.
|
||||
We can then iterate over these names to perform any chosen function.
|
||||
.PP
|
||||
The output of a command within `\`' characters is converted by
|
||||
the shell to a list of words.
|
||||
You can also place the `\`' quoted string within `"' characters
|
||||
to take each (non-empty) line as a component of the variable;
|
||||
preventing the lines from being split into words at blanks and tabs.
|
||||
A modifier `:x' exists which can be used later to expand each component
|
||||
of the variable into another variable splitting it into separate words
|
||||
at embedded blanks and tabs.
|
||||
.NH 2
|
||||
Braces { ... } in argument expansion
|
||||
.PP
|
||||
Another form of filename expansion, alluded
|
||||
to before involves the characters `{' and `}'.
|
||||
These characters specify that the contained strings, separated by `,'
|
||||
are to be consecutively substituted into the containing characters
|
||||
and the results expanded left to right.
|
||||
Thus
|
||||
.DS
|
||||
A{str1,str2,...strn}B
|
||||
.DE
|
||||
expands to
|
||||
.DS
|
||||
Astr1B Astr2B ... AstrnB
|
||||
.DE
|
||||
This expansion occurs before the other filename expansions, and may
|
||||
be applied recursively (i.e. nested).
|
||||
The results of each expanded string are sorted separately, left
|
||||
to right order being preserved.
|
||||
The resulting filenames are not required to exist if no other expansion
|
||||
mechanisms are used.
|
||||
This means that this mechanism can be used to generate arguments which are
|
||||
not filenames, but which have common parts.
|
||||
.PP
|
||||
A typical use of this would be
|
||||
.DS
|
||||
mkdir ~/{hdrs,retrofit,csh}
|
||||
.DE
|
||||
to make subdirectories `hdrs', `retrofit' and `csh'
|
||||
in your home directory.
|
||||
This mechanism is most useful when the common prefix is longer
|
||||
than in this example, i.e.
|
||||
.DS
|
||||
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
|
||||
.DE
|
||||
.NH 2
|
||||
Command substitution
|
||||
.PP
|
||||
A command enclosed in `\`' characters is replaced, just before
|
||||
filenames are expanded, by the output from that command.
|
||||
Thus it is possible to do
|
||||
.DS
|
||||
set pwd=\`pwd\`
|
||||
.DE
|
||||
to save the current directory in the variable
|
||||
.I pwd
|
||||
or to do
|
||||
.DS
|
||||
ex \`grep \-l TRACE *.c\`
|
||||
.DE
|
||||
to run the editor
|
||||
.I ex
|
||||
supplying as arguments those files whose names end in `.c'
|
||||
which have the string `TRACE' in them.*
|
||||
.FS
|
||||
*Command expansion also occurs in input redirected with `<<'
|
||||
and within `"' quotations.
|
||||
Refer to the shell manual section for full details.
|
||||
.FE
|
||||
.NH 2
|
||||
Other details not covered here
|
||||
.PP
|
||||
In particular circumstances it may be necessary to know the exact
|
||||
nature and order of different substitutions performed by the shell.
|
||||
The exact meaning of certain combinations of quotations is also
|
||||
occasionally important.
|
||||
These are detailed fully in its manual section.
|
||||
.PP
|
||||
The shell has a number of command line option flags mostly of use
|
||||
in writing \s-2UNIX\s0 programs,
|
||||
and debugging shell scripts.
|
||||
See the csh(1) manual section for a list of these options.
|
||||
.bp
|
||||
File diff suppressed because it is too large
Load Diff
|
|
@ -0,0 +1,34 @@
|
|||
.\" Copyright (c) 1980, 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. All advertising materials mentioning features or use of this software
|
||||
.\" must display the following acknowledgement:
|
||||
.\" This product includes software developed by the University of
|
||||
.\" California, Berkeley and its contributors.
|
||||
.\" 4. Neither the name of the University nor the names of its contributors
|
||||
.\" 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.
|
||||
.\"
|
||||
.\" @(#)tabs 8.1 (Berkeley) 6/8/93
|
||||
.\"
|
||||
.ta 5n 10n 15n 20n 25n 30n 35n 40n 45n 50n 55n 60n 65n 70n 75n 80n
|
||||
Loading…
Reference in New Issue