csh.1

早期freebsd实现

.Dl % set fignore = (.o .out)
.Pp
then typing
.Pp
.Dl % vi x<escape>
.Pp
would result in the completion to
.Pp
.Dl % vi xmpl.c
.Pp
ignoring the files "xmpl.o" and "xmpl.out".
However, if the only completion possible requires not ignoring these
suffixes, then they are not ignored.  In addition,
.Ar fignore
does not affect the listing of file names by control-D.  All files
are listed regardless of their suffixes.
.Ss Substitutions
We now describe the various transformations the shell performs on the
input in the order in which they occur.
.Ss History substitutions
History substitutions place words from previous command input as portions
of new commands, making it easy to repeat commands, repeat arguments
of a previous command in the current command, or fix spelling mistakes
in the previous command with little typing and a high degree of confidence.
History substitutions begin with the character `!' and may begin
.Ar anywhere
in the input stream (with the proviso that they
.Nm "do not"
nest.)
This `!' may be preceded by a `\e' to prevent its special meaning; for
convenience, an `!' is passed unchanged when it is followed by a blank,
tab, newline, `=' or `('.
(History substitutions also occur when an input line begins with `\*(ua'.
This special abbreviation will be described later.)
Any input line that contains history substitution is echoed on the terminal
before it is executed as it could have been typed without history substitution.
.Pp
Commands input from the terminal that consist of one or more words
are saved on the history list.
The history substitutions reintroduce sequences of words from these
saved commands into the input stream.
The size of the history list is controlled by the
.Ar history
variable; the previous command is always retained,
regardless of the value of the history variable.
Commands are numbered sequentially from 1.
.Pp
For definiteness, consider the following output from the
.Ar history
command:
.Bd -literal -offset indent
\09  write michael
10  ex write.c
11  cat oldwrite.c
12  diff *write.c
.Ed
.Pp
The commands are shown with their event numbers.
It is not usually necessary to use event numbers, but the current event
number can be made part of the
.Ar prompt
by placing an `!' in the prompt string.
.Pp
With the current event 13 we can refer to previous events by event
number `!11', relatively as in `!\-2' (referring to the same event),
by a prefix of a command word
as in `!d' for event 12 or `!wri' for event 9, or by a string contained in
a word in the command as in `!?mic?' also referring to event 9.
These forms, without further change, simply reintroduce the words
of the specified events, each separated by a single blank.
As a special case, `!!' refers to the previous command; thus `!!'
alone is a
.Ar redo .
.Pp
To select words from an event we can follow the event specification by
a `:' and a designator for the desired words.
The words of an input line are numbered from 0,
the first (usually command) word being 0, the second word (first argument)
being 1, etc.
The basic word designators are:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It \&0
first (command) word
.It Ar n
.Ar n Ns 'th
argument
.It \*(ua
first argument,  i.e., `1'
.It $
last argument
.It %
word matched by (immediately preceding)
.No \&? Ns Ar s Ns \&?
search
.It Ar \&x\-y
range of words
.It Ar \&\-y
abbreviates
.Ar `\&0\-y\'
.It *
abbreviates `\*(ua\-$', or nothing if only 1 word in event
.It Ar x*
abbreviates
.Ar `x\-$\'
.It Ar x\-
like
.Ar `x*\'
but omitting word `$'
.El
.Pp
The `:' separating the event specification from the word designator
can be omitted if the argument selector begins with a `\*(ua', `$', `*'
`\-' or `%'.
After the optional word designator can be
placed a sequence of modifiers, each preceded by a `:'.
The following modifiers are defined:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It h
Remove a trailing pathname component, leaving the head.
.It r
Remove a trailing `.xxx' component, leaving the root name.
.It e
Remove all but the extension `.xxx' part.
.It s Ns Ar /l/r/
Substitute
.Ar l
for
.Ar r
.It t
Remove all leading pathname components, leaving the tail.
.It \&&
Repeat the previous substitution.
.It g
Apply the change once on each word, prefixing the above, e.g., `g&'.
.It a
Apply the change as many times as possible on a single word, prefixing
the above. It can be used together with `g' to apply a substitution 
globally.
.It p
Print the new command line but do not execute it.
.It q
Quote the substituted words, preventing further substitutions.
.It x
Like q, but break into words at blanks, tabs and newlines.
.El
.Pp
Unless preceded by a `g' the change is applied only to the first
modifiable word.  With substitutions, it is an error for no word to be
applicable.
.Pp
The left hand side of substitutions are not regular expressions in the sense
of the editors, but instead strings.
Any character may be used as the delimiter in place of `/';
a `\e' quotes the delimiter into the
.Ar l  " "
and
.Ar r  " "
strings.
The character `&' in the right hand side is replaced by the text from
the left.
A `\e' also quotes `&'.
A null
.Ar l
(`//')
uses the previous string either from an
.Ar l
or from a
contextual scan string
.Ar s
in
.No \&`!? Ns Ar s Ns \e?' .
The trailing delimiter in the substitution may be omitted if a newline
follows immediately as may the trailing `?' in a contextual scan.
.Pp
A history reference may be given without an event specification, e.g., `!$'.
Here, the reference is to the previous command unless a previous
history reference occurred on the same line in which case this form repeats
the previous reference.
Thus `!?foo?\*(ua !$' gives the first and last arguments
from the command matching `?foo?'.
.Pp
A special abbreviation of a history reference occurs when the first
non-blank character of an input line is a `\*(ua'.
This is equivalent to `!:s\*(ua' providing a convenient shorthand for substitutions
on the text of the previous line.
Thus `\*(ualb\*(ualib' fixes the spelling of
`lib'
in the previous command.
Finally, a history substitution may be surrounded with `{' and `}'
if necessary to insulate it from the characters that follow.
Thus, after `ls \-ld ~paul' we might do `!{l}a' to do `ls \-ld ~paula',
while `!la' would look for a command starting with `la'.
.Pp
.Ss Quotations with \' and \&"
The quotation of strings by `\'' and `"' can be used
to prevent all or some of the remaining substitutions.
Strings enclosed in `\'' are prevented any further interpretation.
Strings enclosed in `"' may be expanded as described below.
.Pp
In both cases the resulting text becomes (all or part of) a single word;
only in one special case (see
.Em Command Substitution
below) does a `"' quoted string yield parts of more than one word;
`\'' quoted strings never do.
.Ss Alias substitution
The shell maintains a list of aliases that can be established, displayed
and modified by the
.Ar alias
and
.Ar unalias
commands.
After a command line is scanned, it is parsed into distinct commands and
the first word of each command, left-to-right, is checked to see if it
has an alias.
If it does, then the text that is the alias for that command is reread
with the history mechanism available
as though that command were the previous input line.
The resulting words replace the
command and argument list.
If no reference is made to the history list, then the argument list is
left unchanged.
.Pp
Thus if the alias for `ls' is `ls \-l' the command `ls /usr' would map to
`ls \-l /usr', the argument list here being undisturbed.
Similarly if the alias for `lookup' was `grep !\*(ua /etc/passwd' then
`lookup bill' would map to `grep bill /etc/passwd'.
.Pp
If an alias is found, the word transformation of the input text
is performed and the aliasing process begins again on the reformed input line.
Looping is prevented if the first word of the new text is the same as the old
by flagging it to prevent further aliasing.
Other loops are detected and cause an error.
.Pp
Note that the mechanism allows aliases to introduce parser metasyntax.
Thus, we can `alias print \'pr \e!* \&| lpr\'' to make a command that
.Ar pr Ns 's
its arguments to the line printer.
.Ss Variable substitution
The shell maintains a set of variables, each of which has as value a list
of zero or more words.
Some of these variables are set by the shell or referred to by it.
For instance, the
.Ar argv
variable is an image of the shell's argument list, and words of this
variable's value are referred to in special ways.
.Pp
The values of variables may be displayed and changed by using the
.Ar set
and
.Ar unset
commands.
Of the variables referred to by the shell a number are toggles;
the shell does not care what their value is,
only whether they are set or not.
For instance, the
.Ar verbose
variable is a toggle that causes command input to be echoed.
The setting of this variable results from the
.Fl v
command line option.
.Pp
Other operations treat variables numerically.
The `@' command permits numeric calculations to be performed and the result
assigned to a variable.
Variable values are, however, always represented as (zero or more) strings.
For the purposes of numeric operations, the null string is considered to be
zero, and the second and additional words of multiword values are ignored.
.Pp
After the input line is aliased and parsed, and before each command
is executed, variable substitution
is performed keyed by `$' characters.
This expansion can be prevented by preceding the `$' with a `\e' except
within `"'s where it
.Em always
occurs, and within `\''s where it
.Em never
occurs.
Strings quoted by `\*(ga' are interpreted later (see
.Nm "Command substitution"
below) so `$' substitution does not occur there until later, if at all.
A `$' is passed unchanged if followed by a blank, tab, or end-of-line.
.Pp
Input/output redirections are recognized before variable expansion,
and are variable expanded separately.
Otherwise, the command name and entire argument list are expanded together.
It is thus possible for the first (command) word (to this point) to generate
more than one word, the first of which becomes the command name,
and the rest of which become arguments.
.Pp
Unless enclosed in `"' or given the `:q' modifier the results of variable
substitution may eventually be command and filename substituted.
Within `"', a variable whose value consists of multiple words expands to a
(portion of) a single word, with the words of the variables value
separated by blanks.
When the `:q' modifier is applied to a substitution
the variable will expand to multiple words with each word separated
by a blank and quoted to prevent later command or filename substitution.
.Pp
The following metasequences are provided for introducing variable values into
the shell input.
Except as noted, it is an error to reference a variable that is not set.
.Pp
.Bl -tag -width Ds -compact -offset indent
.It $name
.It ${name}
Are replaced by the words of the value of variable
.Ar name ,
each separated by a blank.
Braces insulate
.Ar name
from following characters that would otherwise be part of it.
Shell variables have names consisting of up to 20 letters and digits
starting with a letter.  The underscore character is considered a letter.
If
.Ar name
is not a shell variable, but is set in the environment, then
that value is returned (but
.Nm :
modifiers and the other forms
given below are not available here).
.It $name Ns Op selector
.It ${name Ns [ selector ] }
May be used to select only some of the words from the value of
.Ar name .
The selector is subjected to `$' substitution and may consist of a single
number or two numbers separated by a `\-'.
The first word of a variables value is numbered `1'.
If the first number of a range is omitted it defaults to `1'.
If the last number of a range is omitted it defaults to `$#name'.
The selector `*' selects all words.
It is not an error for a range to be empty if the second argument is omitted
or in range.
.It $#name
.It ${#name}
Gives the number of words in the variable.
This is useful for later use in a
`$argv[selector]'.
.It $0
Substitutes the name of the file from which command input is being read.
An error occurs if the name is not known.
.It $number
.It ${number}
Equivalent to
`$argv[number]'.
.It $*
Equivalent to
`$argv[*]'.
The modifiers `:e', `:h', `:t', `:r', `:q' and `:x' may be applied to
the substitutions above as may `:gh', `:gt' and `:gr'.
If braces `{' '}' appear in the command form then the modifiers
must appear within the braces.
The current implementation allows only one `:' modifier on each `$' expansion.
.El
.Pp
The following substitutions may not be modified with `:' modifiers.
.Bl -tag -width Ds -compact -offset indent
.It $?name
.It ${?name}
Substitutes the string `1' if name is set, `0' if it is not.
.It $?0
Substitutes `1' if the current input filename is known, `0' if it is not.
.It \&$\&$\&
Substitute the (decimal) process number of the (parent) shell.
.It $!
Substitute the (decimal) process number of the last background process
started by this shell.
.It $<
Substitutes a line from the standard
input, with no further interpretation.
It can be used to read from the keyboard in a shell script.
.El
.Ss Command and filename substitution
The remaining substitutions, command and filename substitution,
are applied selectively to the arguments of builtin commands.
By selectively, we mean that portions of expressions which are
not evaluated are not subjected to these expansions.
For commands that are not internal to the shell, the command
name is substituted separately from the argument list.
This occurs very late,
after input-output redirection is performed, and in a child
of the main shell.
.Ss Command substitution
Command substitution is shown by a command enclosed in `\*(ga'.
The output from such a command is normally broken into separate words
at blanks, tabs and newlines, with null words being discarded;
this text then replaces the original string.
Within `"'s, only newlines force new words; blanks and tabs are preserved.
.Pp
In any case, the single final newline does not force a new word.
Note that it is thus possible for a command substitution to yield
only part of a word, even if the command outputs a complete line.
.Ss Filename substitution
If a word contains any of the characters `*', `?', `[' or `{'
or begins with the character `~', then that word is a candidate for
filename substitution, also known as `globbing'.
This word is then regarded as a pattern, and replaced with an alphabetically
sorted list of file names that match the pattern.
In a list of words specifying filename substitution it is an error for
no pattern to match an existing file name, but it is not required
for each pattern to match.
Only the metacharacters `*', `?' and `[' imply pattern matching,
the characters `~' and `{' being more akin to abbreviations.
.Pp
In matching filenames, the character `.' at the beginning of a filename
or immediately following a `/', as well as the character `/' must
be matched explicitly.
The character `*' matches any string of characters, including the null
string.
The character `?' matches any single character.
The sequence
.Sq Op ...
matches any one of the characters enclosed.
Within
.Sq Op ... ,
a pair of characters separated by `\-' matches any character lexically between
the two (inclusive).
.Pp
The character `~' at the beginning of a filename refers to home
directories.