sh.html

unix 下的C开发手册,还用详细的例程。

Tilde Expansion
</a></xref>.

<dt><i>IFS</i><dd><i>Input field separators :</i>
a string treated as a list of characters
that is used for field splitting and to
split lines into words with the
<i><a href="read.html">read</a></i>
command.
See
<xref href=fldspl><a href="chap2.html#tag_001_006_005">
Field Splitting
</a></xref>.
If
<i>IFS</i>
is not set, the shell behaves as if the value of
<i>IFS</i>
were the
space,
tab
and
newline
characters.
Implementations may ignore the value of
<i>IFS</i>
in the environment at the time
<i>sh</i>
is invoked, treating
<i>IFS</i>
as if it were not set.

<dt><i>LANG</i><dd>Provide a default value for the internationalisation variables
that are unset or null.
If
<i>LANG</i>
is unset or null, the corresponding value from the
implementation-dependent default locale will be used.
If any of the internationalisation variables contains an invalid setting, the
utility will behave as if none of the variables had been defined.

<dt><i>LC_ALL</i><dd>
If set to a non-empty string value,
override the values of all the other internationalisation variables.

<dt><i>LC_COLLATE</i><dd>
Determine the behaviour of range
expressions, equivalence classes and multi-character collating elements
within pattern matching.

<dt><i>LC_CTYPE</i><dd>
Determine the
locale for the interpretation of sequences of bytes of text data
as characters (for example, single-
versus multi-byte characters in arguments and input files),
which characters are defined as
letters (character class
<b>alpha</b>),
and the behaviour of character classes within pattern matching.

<dt><i>LC_MESSAGES</i><dd>
Determine the locale that should be used to affect
the format and contents of diagnostic
messages written to standard error.

<dt><i>MAIL</i><dd>Determine a pathname of the user's mailbox file
for purposes of incoming mail notification.
If this variable is set,
the shell will inform the user if the file named
by the variable is created or if its modification time has changed.
Informing the user is accomplished by writing a string
of unspecified format
to standard error prior to the writing of
the next primary prompt string
after the completion of an interval defined by the
<i>MAILCHECK</i>
variable.
The user will be informed only if
<i>MAIL</i>
is set and
<i>MAILPATH</i>
is not set.

<dt><i>MAILCHECK</i><dd>
Establish a decimal integer
value that specifies how often (in seconds) the shell
will check for the arrival of mail in the files specified by the
<i>MAILPATH</i>
or
<i>MAIL</i>
variables.
The default value is 600 seconds.
If set to zero, the shell will check before issuing each primary prompt.

<dt><i>MAILPATH</i><dd>
Provide a list of pathnames
and optional messages separated by colons.
If this variable is set, the shell will inform
the user if any of the files named by the variable are created or
if any of their modification times change.
(See the preceding entry for
<i>MAIL</i>
for descriptions of mail arrival and user informing.)
Each pathname can be followed by
"%"
and a string that will be
subjected to parameter expansion and
written to standard error when the
modification time changes.
If a
"%"
character in the pathname is preceded by a backslash,
it will be treated as a literal
"%"
in the pathname.
The default message is unspecified.

The
<i>MAILPATH</i>
environment variable takes precedence over the
<i>MAIL</i>
variable.

<dt><i>NLSPATH</i><dd>
Determine the location of message catalogues
for the processing of
<i>LC_MESSAGES .
</i>
<dt><i>PATH</i><dd>Establish a string formatted as described in
the <b>XBD</b> specification, <a href="../xbd/envvar.html"><b>Environment Variables</b>&nbsp;</a> ,
used to effect command interpretation.
See
<xref href=cmdsea><a href="chap2.html#tag_001_009_001_001">
Command Search and Execution
</a></xref>.

</dl>
</blockquote><h4><a name = "tag_001_014_2000">&nbsp;</a>ASYNCHRONOUS EVENTS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_2001">&nbsp;</a>STDOUT</h4><blockquote>
See the STDERR section.
<br>
</blockquote><h4><a name = "tag_001_014_2002">&nbsp;</a>STDERR</h4><blockquote>
Except as otherwise stated (by the descriptions of any
invoked utilities or in interactive mode),
standard error is
used only for diagnostic messages.
</blockquote><h4><a name = "tag_001_014_2003">&nbsp;</a>OUTPUT FILES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_2004">&nbsp;</a>EXTENDED DESCRIPTION</h4><blockquote>
See
<xref href=shell><a href="chap2.html#tag_001">
Shell Command Language
</a></xref>.
The following additional capabilities are supported.
<h5><a name = "tag_001_014_2004_001">&nbsp;</a>Command History List</h5>
<xref type="5" name="shcmdhist"></xref>
When the
<i>sh</i>
utility is being used interactively,
it maintains a list of commands previously entered
from the terminal
in the file named by the
<i>HISTFILE</i>
environment variable.
The type, size and internal format of this file are unspecified.
Multiple
<i>sh</i>
processes can share access to the file for a user,
if file access permissions allow this;
see the description of the
<i>HISTFILE</i>
environment variable.
<h5><a name = "tag_001_014_2004_002">&nbsp;</a>Command Line Editing</h5>
When
<i>sh</i>
is being used interactively from a terminal, the current
command and the command history (see
<i><a href="fc.html">fc</a></i>)
can be edited using
<i>vi-mode</i>
command line editing.
This mode uses commands, described below,
similar to a subset of those described in the
<i><a href="vi.html">vi</a></i>
utility.
Implementations may offer other command line editing modes
corresponding to other editing utilities.
<p>
The command
<i>set</i>
<b>-o</b>
<b>v</b>
enables vi-mode editing and places
<i>sh</i>
into
<i><a href="vi.html">vi</a></i>
insert mode (see
<xref href=shvicle><a href="#tag_001_014_2004_003">
Command Line Editing (vi-mode)
</a></xref>).
This command also disables any other
editing mode that the implementation may provide.
The command
<i>set</i>
<b>+o</b>
<b>v</b>
disables vi-mode editing.
<p>
Certain block-mode terminals may be unable to support shell command
line editing.
If a terminal is unable to provide either edit mode,
it need not be possible to
<i>set</i>
<b>-o</b>
<b>v</b>
when using the shell on this terminal.
<p>
In the following sections, the characters
erase,
interrupt,
kill
and
end-of-file
are those set by the
<i><a href="stty.html">stty</a></i>
utility.
<h5><a name = "tag_001_014_2004_003">&nbsp;</a>Command Line Editing (vi-mode)</h5>
<xref type="5" name="shvicle"></xref>
With vi-mode enabled,
<i>sh</i>
can be switched between insert mode and command mode.
<p>
When in insert mode, an entered character
will be inserted into the command line,
except as noted in
<xref href=shvieim><a href="#tag_001_014_2004_004">
vi Line Editing Insert Mode
</a></xref>.
Upon entering
<i>sh</i>
and after termination of the previous command,
<i>sh</i>
will be in insert mode.
<p>
Typing an escape character wll switch
<i>sh</i>
into command mode (see
<xref href=shviecm><a href="#tag_001_014_2004_005">
vi Line Editing Command Mode
</a></xref>).
In command mode, an entered character will either invoke a defined
operation, be used as part of a multi-character operation
or be treated as an error.
A character that is not recognised as part of an editing
command will terminate any specific editing command and
will alert the terminal.
Typing the
<i>interrupt</i>
character in command mode will cause
<i>sh</i>
to terminate command line editing on the
current command line, reissue the
prompt on the next line of the terminal
and reset the command history (see
<i><a href="fc.html">fc</a></i>)
so that the most recently executed command
is the previous command (that is, the
command that was being edited when it was
interrupted is not reentered into the history).
<p>
In the following sections, the phrase &quot;move the cursor to the
beginning of the word&quot; means &quot;move the cursor to the first
character of the current word&quot; and the phrase &quot;move the cursor to the
end of the word&quot; means &quot;move the cursor to the last
character of the current word&quot;.
The phrase &quot;beginning of the command line&quot; indicates
the point between the end of the prompt string issued by the shell
(or the beginning of the terminal line, if there is no prompt string)
and the first character of the command text.
<h5><a name = "tag_001_014_2004_004">&nbsp;</a>vi Line Editing Insert Mode</h5>
<xref type="5" name="shvieim"></xref>
While in insert mode, any character typed will be inserted in the
current command line, unless it is from the following set.
<dl compact>

<dt>newline<dd>
Execute the current command line being edited.

<dt><i>erase</i><dd>Delete the character previous to the current cursor position
and move the current cursor position back one character.
In insert mode, characters will be erased from both the screen and
the buffer when backspacing.

<dt><i>interrupt</i><dd>
Terminate command line editing with the same effects
as described for interrupting command mode; see
<xref href=shvicle><a href="#tag_001_014_2004_003">
Command Line Editing (vi-mode)
</a></xref>.

<dt><i>kill</i><dd>Clear all the characters from the input line.

<dt>&lt;control&gt;-V<dd>
Insert the next character input, even if the character
is otherwise a special insert mode character.

<dt>&lt;control&gt;-W<dd>
Delete the characters from the one preceding the cursor to
the preceding word boundary.
The word boundary in this case
is the closer to the cursor of
either the beginning of the line or a character that is
in neither the
<b>blank</b>
nor
<b>punct</b>
character classification of the current locale.

<dt><b>\</b><dd>On some systems, when a backslash is followed by an
<i>erase</i>
or
<i>kill</i>
character, that character will be inserted into the input line.
This is not actually a feature of
<i>sh</i>
command line editing insert mode, but one of
terminal line drivers when the
<i><a href="stty.html">stty</a></i>
<b>iexten</b>
flag is set.
Otherwise, the backslash itself will be inserted into the input line.

<dt><i>end-of-file</i><dd>

Interpreted as the end of input in
<i>sh</i>.
This interpretation will occur only at the beginning of an input line.
If end-of-file is entered other than at the beginning of the line,
the results are unspecified.

<dt>&lt;ESC&gt;<dd>Place
<i>sh</i>
into command mode.

</dl>
<h5><a name = "tag_001_014_2004_005">&nbsp;</a>vi Line Editing Command Mode</h5>
<xref type="5" name="shviecm"></xref>
In command mode for the command line editing feature, decimal
digits not beginning with 0 that precede a command letter will be remembered.
Some commands use these decimal digits as a count number
that affects the operation.
<p>
The term
<i>motion command</i>
represents one of the commands:
<pre>
<code>
&lt;space&gt;  0  b  F  l  W  ^  $  ;  E  f  T  w  |  ,  B  e  h  t
</code>
</pre>
<p>
Any command that modifies the current line will cause a copy of the
current line to be made at the end of the
command history, the current
line will become that copy,
and the edit will be performed on that copy.
<p>
Any command that is preceded by
<i>count</i>
will take a count (the numeric
value of any preceding decimal digits).
Unless otherwise noted, this
count will cause the specified operation to repeat by the number of
times specified by the count.
Also unless otherwise noted, a
<i>count</i>
that is out of range is considered an error condition and
will alert the terminal,
but neither the cursor position,
nor the command line, will change.
<p>
The terms
<i>word</i>
and
<i>bigword</i>
are used as defined in the
<i><a href="vi.html">vi</a></i>
description.
The term
<i>save buffer</i>
corresponds to the term
<i>unnamed buffer</i>
in
<i><a href="vi.html">vi</a></i>.