table of contents
CSH(1) | General Commands Manual | CSH(1) |
NAME¶
csh
—
a shell (command interpreter) with C-like
syntax
SYNOPSIS¶
csh |
[-bcefimnstVvXx argument ... ] |
csh |
[-l |
DESCRIPTION¶
csh
is a command language interpreter
incorporating a history mechanism (see
History
substitutions), job control facilities (see
Jobs), interactive file name and
user name completion (see
File name
completion), and a C-like syntax. It is used both as an interactive login
shell and a shell script command processor.
Argument list processing¶
If the first argument (argument 0) to the shell is a dash (‘-’), then this is a login shell. A login shell also can be specified by invoking the shell with the-l
flag as the only
argument.
The rest of the flag arguments are interpreted as follows:
-b
- This flag forces a “break” from option processing, causing any further shell arguments to be treated as non-option arguments. The remaining arguments will not be interpreted as shell options. This may be used to pass options to a shell script without confusion or possible subterfuge. The shell will not run a set-user-ID script without this option.
-c
- Commands are read from the (single) following argument which must be present. Any remaining arguments are placed in argv.
-e
- The shell exits if any invoked command terminates abnormally or yields a non-zero exit status.
-f
- The shell will start faster, because it will neither search for nor
execute commands from the file .cshrc
in the invoker's home directory. Note: if the environment variable
HOME
is not set, fast startup is the default. -i
- The shell is interactive and prompts for its top-level input, even if it appears not to be a terminal. Shells are interactive without this option if their inputs and outputs are terminals.
-l
- The shell is a login shell (only applicable if
-l
is the only flag specified). -m
- Read .cshrc, regardless of its owner and group. This option is dangerous and should only be used by su(1).
-n
- Commands are parsed, but not executed. This aids in syntactic checking of
shell scripts. When used interactively, the shell can be terminated by
pressing control-D (end-of-file character), since
exit
will not work. -s
- Command input is taken from the standard input.
-t
- A single line of input is read and executed. A backslash
(‘
\
’) may be used to escape the newline at the end of this line and continue onto another line. -V
- Causes the verbose variable to be set even before .cshrc is executed.
-v
- Causes the verbose variable to be set, with the effect that command input is echoed after history substitution.
-X
- Causes the echo variable to be set even before .cshrc is executed.
-x
- Causes the echo variable to be set, so that commands are echoed immediately before execution.
-c
, -i
,
-s
, or
-t
options were given, the first argument
is taken as the name of a file of commands to be executed. The shell opens
this file, and saves its name for possible resubstitution by
‘$0’. Since many systems use either the standard version 6 or
version 7 shells whose shell scripts are not compatible with this shell, the
shell will execute such a “standard” shell if the first
character of a script is not a hash mark
(‘#
’); i.e., if the script does not
start with a comment. Remaining arguments initialize the variable
argv.
An instance of csh
begins by executing
commands from the file /etc/csh.cshrc and,
if this is a login shell, /etc/csh.login.
It then executes commands from .cshrc in
the home directory of the invoker, and, if this is a login shell, the file
.login in the same location. It is typical
for users on CRTs to put the command stty
crt
in their .login file, and to
also invoke tset(1) there.
In the normal case, the shell will begin reading commands from the terminal,
prompting with ‘% .’ Processing of arguments and the use
of the shell to process files containing command scripts will be described
later.
The shell repeatedly performs the following actions: a line of command input is
read and broken into “words”. This sequence of words is placed
on the command history list and parsed. Finally each command in the current
line is executed.
When a login shell terminates it executes commands from the files
.logout in the user's home directory and
/etc/csh.logout.
Lexical structure¶
The shell splits input lines into words at blanks and tabs with the following exceptions. The characters ‘&
’,
‘|
’,
‘;
’,
‘<
’,
‘>
’,
‘(
’, and
‘)
’ form separate words. If doubled in
‘&&
’,
‘||
’,
‘<<
’, or
‘>>
’, these pairs form single
words. These parser metacharacters may be made part of other words, or have
their special meaning prevented, by preceding them with a backslash
(‘\
’). A newline preceded by a
‘\
’ is equivalent to a blank.
Strings enclosed in matched pairs of quotations,
‘'
’,
‘`
’, or
‘"
’, form parts of a word;
metacharacters in these strings, including blanks and tabs, do not form
separate words. These quotations have semantics to be described later. Within
pairs of ‘'
’ or
‘"
’ characters, a newline preceded
by a ‘\
’ gives a true newline character.
When the shell's input is not a terminal, the character
‘#
’ introduces a comment that continues
to the end of the input line. This special meaning is prevented when preceded
by ‘\
’ and in quotations using
‘`
’,
‘'
’, and
‘"
’.
Commands¶
A simple command is a sequence of words, the first of which specifies the command to be executed. A simple command or a sequence of simple commands separated by ‘|
’ characters forms a
pipeline. The output of each command in a pipeline is connected to the input
of the next. Sequences of pipelines may be separated by
‘;
’, and are then executed sequentially.
A sequence of pipelines may be executed without immediately waiting for it to
terminate by following it with a
‘&
’.
Any of the above may be placed in ‘(
’
‘)
’ to form a simple command (that may
be a component of a pipeline, for example). It is also possible to separate
pipelines with ‘||
’ or
‘&&
’ showing, as in the C
language, that the second is to be executed only if the first fails or
succeeds, respectively. (See Expressions.)
Jobs¶
The shell associates a job with each pipeline. It keeps a table of current jobs, printed by thejobs
command, and assigns them small
integer numbers. When a job is started asynchronously with
‘&
’, the shell prints a line that
looks like:
[
showing that the job which was started asynchronously was job number 1 and had
one (top-level) process, whose process ID was 1234.
If you are running a job and wish to do something else you may hit
1
] 1234^Z
(control-Z), which sends a
SIGSTOP
signal to the current job. The
shell will then normally show that the job has been “Stopped”,
and print another prompt. You can then manipulate the state of this job,
putting it in the background with the
bg
command, or run some other commands and
eventually bring the job back into the foreground
with the fg
command. A
^Z
takes effect immediately and is like an
interrupt in that pending output and unread input are discarded when it is
typed. There is another special key ^Y
that
does not generate a SIGSTOP
signal until a
program attempts to read(2) it. This request can
usefully be typed ahead when you have prepared some commands for a job that
you wish to stop after it has read them.
A job being run in the background will stop if it tries to read from the
terminal. Background jobs are normally allowed to produce output, but this can
be disabled by giving the command stty
tostop
. If you set this tty option, then background jobs will stop when
they try to produce output like they do when they try to read input.
There are several ways to refer to jobs in the shell. The character
‘%
’ introduces a job name. If you wish
to refer to job number 1, you can name it as
‘%1
’. Just naming a job brings it to the
foreground; thus %1
is a synonym for
fg %1
, bringing job number 1 back into the
foreground. Similarly, saying %1 &
resumes job number 1 in the background. Jobs can also be named by prefixes of
the string typed in to start them, if these prefixes are unambiguous; thus
%ex
would normally restart a suspended
ex(1) job, if there were only one suspended job
whose name began with the string “ex”. It is also possible to
say %?string
, which specifies a job whose
text contains string, if there is only one
such job.
The shell maintains a notion of the current and previous jobs. In output about
jobs, the current job is marked with a
‘+
’ and the previous job with a
‘-
’. The abbreviation
‘%+
’ refers to the current job and
‘%-
’ refers to the previous job. For
close analogy with the syntax of the
history
mechanism (described below),
‘%%
’ is also a synonym for the current
job.
The job control mechanism requires that the stty(1)
option new
be set. It is an artifact from a
new implementation of the tty driver that allows
generation of interrupt characters from the keyboard to tell jobs to stop. See
stty(1) for details on setting options in the new
tty driver.
Status reporting¶
The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. If, however, you set the shell variable notify, the shell will notify you immediately of changes of status in background jobs. There is also a shell commandnotify
that marks a single process so that
its status changes will be immediately reported. By default
notify
marks the current process; simply
say notify
after starting a background job
to mark it.
When you try to leave the shell while jobs are stopped, you will be warned that
“You have stopped jobs”. You may use the
jobs
command to see what they are. If you
try to exit again immediately, the shell will not warn you a second time, and
the suspended jobs will be terminated.
File name completion¶
When the file name completion feature is enabled by setting the shell variable filec (seeset
),
csh
will interactively complete file names
and user names from unique prefixes when they are input from the terminal
followed by the escape character (the escape key, or control-[). For example,
if the current directory looks like
DSC.OLD bin cmd lib xmpl.c DSC.NEW chaosnet cmtest mail xmpl.o bench class dev mbox xmpl.out
% vi ch<escape>
csh
will complete the prefix
“ch” to the only matching file name “chaosnet”,
changing the input line to
% vi chaosnet
% vi D<escape>
csh
will only expand the input to
% vi DSC.
D
’.
If a partial file name is followed by the end-of-file character (usually
control-D), then, instead of completing the name,
csh
will list all file names matching the
prefix. For example, the input
% vi D<control-D>
D
’ to be
listed:
DSC.NEW DSC.OLD
~
’). For example, typing
cd ~ro<escape>
cd ~root
% set fignore = (.o
.out)
% vi x<escape>
% vi xmpl.c
Substitutions¶
We now describe the various transformations the shell performs on the input in the order in which they occur.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
anywhere in the input stream (with the proviso
that they do not nest). This
‘!
’ may be preceded by a
‘\
’ to prevent its special meaning; for
convenience, a ‘!
’ character is passed
unchanged when it is followed by a blank, tab, newline,
‘=
’ or
‘(
’. (History substitutions also occur
when an input line begins with ‘^
’. 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
would have been typed without history substitution.
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 history variable; the
previous command is always retained, regardless of the value of the history
variable. Commands are numbered sequentially from 1.
For definiteness, consider the following output from the
history
command:
09 write michael 10 ex write.c 11 cat oldwrite.c 12 diff *write.c
!
’ in the prompt string.
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
redo.
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:
- 0
- first (command) word
- n
- n'th argument
- ^
- first argument; i.e., ‘
1
’ - $
- last argument
- %
- word matched by (immediately preceding) ?s? search
- x-y
- range of words
- -y
- abbreviates ‘
0-y
’ - *
- abbreviates ‘
^-$
’, or nothing if only 1 word in event - x*
- abbreviates ‘
x-$
’ - x-
- like ‘
x*
’ but omitting word ‘$
’
:
’ separating the event specification
from the word designator can be omitted if the argument selector begins with a
‘^
’,
‘$
’,
‘*
’,
‘-
’, or
‘%
’. After the optional word designator,
a sequence of modifiers can be placed, each preceded by a
‘:
’. The following modifiers are
defined:
- h
- Remove a trailing pathname component, leaving the head.
- r
- Remove a trailing ‘
.xxx
’ component, leaving the root name. - e
- Remove all but the extension ‘
.xxx
’ part. - s/l/r/
- Substitute l for r.
- t
- Remove all leading pathname components, leaving the tail.
- &
- Repeat the previous substitution.
- g
- Apply the change once on each word, prefixing the above; e.g.,
‘
g&
’. - 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. - p
- Print the new command line but do not execute it.
- q
- Quote the substituted words, preventing further substitutions.
- x
- Like ‘
q
’, but break into words at blanks, tabs, and newlines.
g
’ the change is
applied only to the first modifiable word. With substitutions, it is an error
for no word to be applicable.
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
‘\
’ quotes the delimiter into the
l and r
strings. The character ‘&
’ in the
right-hand side is replaced by the text from the left. A
‘\
’ also quotes
‘&
’. A
NULL
l
(‘//
’) uses the previous string either
from an l or from a contextual scan string
s in
‘!?s\?
’.
The trailing delimiter in the substitution may be omitted if a newline follows
immediately as may the trailing ‘?
’ in a
contextual scan.
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?^
!$” gives the first and last arguments from the command matching
“?foo?”.
A special abbreviation of a history reference occurs when the first non-blank
character of an input line is a ‘^
’.
This is equivalent to “!:s^” providing a convenient shorthand
for substitutions on the text of the previous line. Thus
^lb^lib
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”.
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 from any further
interpretation. Strings enclosed in
‘"
’ may be expanded as described
below.
In both cases the resulting text becomes (all or part of) a single word; only in
one special case (see Command Substitution below)
does a ‘"
’ quoted string yield
parts of more than one word; ‘'
’ quoted
strings never do.
Alias substitution¶
The shell maintains a list of aliases that can be established, displayed and modified by thealias
and
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.
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 !^ /etc/passwd” then lookup
bill
would map to grep bill
/etc/passwd
.
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.
Note that the mechanism allows aliases to introduce parser metasyntax. Thus, we
can alias print 'pr \!* | lpr'
to make a
command that pr
's its arguments to the line
printer.
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 argv variable is an image of the shell's argument list, and words of this variable's value are referred to in special ways. The values of variables may be displayed and changed by using theset
and
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
verbose variable is a toggle that causes
command input to be echoed. The setting of this variable results from the
-v
command-line option.
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.
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
‘\
’ except within double quotes
(`"'), where it always occurs, and within
single quotes (`''), where it never occurs.
Strings quoted by backticks (` `) are interpreted later (see
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.
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.
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 variable's 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.
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.
- $name
- ${name}
- Are replaced by the words of the value of variable
name, each separated by a blank. Braces
insulate 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 name
is not a shell variable, but is set in the environment, then that value is
returned (but ‘
:
’ modifiers and the other forms given below are not available here). - $name[selector]
- ${name[selector]}
- May be used to select only some of the words from the value of
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 variable's 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. - $#name
- ${#name}
- Gives the number of words in the variable. This is useful for later use in a “$argv[selector]”.
- $0
- Substitutes the name of the file from which command input is being read. An error occurs if the name is not known.
- $number
- ${number}
- Equivalent to “$argv[number]”.
- $*
- Equivalent to “$argv[*]”.
: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.
The following substitutions may not be modified with
‘:
’ modifiers.
- $?name
- ${?name}
- Substitutes the string “1” if name is set, “0” if it is not.
- $?0
- Substitutes ‘
1
’ if the current input filename is known, ‘0
’ if it is not. - $$
- Substitute the (decimal) process number of the (parent) shell. Do NOT use this mechanism for generating temporary file names; see mktemp(1) instead.
- $!
- Substitute the (decimal) process number of the last background process started by this shell.
- $<
- Substitutes a line from the standard input, with no further interpretation. It can be used to read from the keyboard in a shell script.
Command and filename substitution¶
The remaining substitutions, command and filename substitution, are applied selectively to the arguments of built-in 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.Command substitution¶
Command substitution is shown by a command enclosed in ‘`
’. 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
double quotes (`"'), only newlines force new words; blanks and tabs are
preserved.
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.
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.
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 “[...
]” matches any one of the
characters enclosed. Within “[...
]”, a
pair of characters separated by ‘-
’
matches any character lexically between the two (inclusive). Within
“[...
]”, the name of a
character class enclosed in ‘[:’
and ‘:]’ stands for the list of all characters belonging to that
class. Supported character classes:
alnum |
cntrl | lower | space |
alpha |
digit | upper | |
blank |
graph | punct | xdigit |
~
’ at the beginning of a
filename refers to home directories. Standing alone, i.e.,
‘~
’, it expands to the invoker's home
directory as reflected in the value of the variable
home. When followed by a name consisting of
letters, digits, and ‘-
’ characters, the
shell searches for a user with that name and substitutes their home directory;
thus “~ken” might expand to “/usr/ken” and
“~ken/chmach” to “/usr/ken/chmach”. If the
character ‘~
’ is followed by a character
other than a letter or ‘/
’, or does not
appear at the beginning of a word, it is left undisturbed.
The metanotation “a{b,c,d}e” is a shorthand for “abe ace
ade”. Left to right order is preserved, with results of matches being
sorted separately at a low level to preserve this order. This construct may be
nested. Thus, “~source/s1/{oldls,ls}.c” expands to
“/usr/source/s1/oldls.c /usr/source/s1/ls.c” without chance of
error if the home directory for “source” is
“/usr/source”. Similarly “../{memo,*box}” might
expand to “../memo ../box ../mbox”. (Note that
“memo” was not sorted with the results of the match to
“*box”.) As a special case
‘{
’,
‘}
’, and
‘{}
’ are passed undisturbed.
Input/output¶
The standard input and the standard output of a command may be redirected with the following syntax:- < name
- Open file name (which is first variable, command, and filename expanded) as the standard input.
- << word
- Read the shell input up to a line that is identical to
word.
word is not subjected to variable,
command, or filename substitution, and each input line is compared to
word before any substitutions are done on
the input line. Unless a quoting
‘
\
’, ‘"
’, ‘'
’ or ‘`
’ appears in word, variable and command substitution is performed on the intervening lines, allowing ‘\
’ to quote ‘$
’, ‘\
’ and ‘`
’. Commands that are substituted have all blanks, tabs, and newlines preserved, except for the final newline which is dropped. The resultant text is placed in an anonymous temporary file that is given to the command as its standard input. - > name
- >! name
- >& name
- >&! name
- The file name is used as the standard
output. If the file does not exist then it is created; if the file exists,
it is truncated; its previous contents are lost.
If the variable noclobber is set, then the
file must not exist or be a character special file (e.g., a terminal or
/dev/null) or an error results. This
helps prevent accidental destruction of files. Here, the
‘
!
’ forms can be used to suppress this check. The forms involving ‘&
’ route the standard error output into the specified file as well as the standard output. name is expanded in the same way as ‘<
’ input filenames are. - >> name
- >>& name
- >>! name
- >>&! name
- Uses file name as the standard output;
like ‘
>
’ but places output at the end of the file. If the variable noclobber is set, then it is an error for the file not to exist unless one of the ‘!
’ forms is given. Otherwise similar to ‘>
’.
<<
’ mechanism should be used to
present inline data. This permits shell command scripts to function as
components of pipelines and allows the shell to block read its input. Note
that the default standard input for a command run detached is
not modified to be the empty file
/dev/null; instead the standard input
remains as the original standard input of the shell. If this is a terminal and
if the process attempts to read from the terminal, then the process will block
and the user will be notified (see
Jobs above).
The standard error output may be directed through a pipe with the standard
output. Simply use the form ‘|&
’
instead of just ‘|
’.
Expressions¶
Several of the built-in commands (to be described later) take expressions, in which the operators are similar to those of C, with the same precedence, but with the opposite grouping: right to left. These expressions appear in the@
,
exit
,
if
, and
while
commands. The following operators are
available:
|| && | ↑ & == != =~ !~ <= >=
< > << >> + - * / % ! ~ ( )
Here the precedence increases to the right,
‘==
’
‘!=
’
‘=~
’ and
‘!~
’,
‘<=
’
‘>=
’
‘<
’ and
‘>
’,
‘<<
’ and
‘>>
’,
‘+
’ and
‘-
’,
‘*
’
‘/
’ and
‘%
’ being, in groups, at the same level.
The ‘==
’
‘!=
’
‘=~
’ and
‘!~
’ operators compare their arguments
as strings; all others operate on numbers. The operators
‘=~
’ and
‘!~
’ are like
‘!=
’ and
‘==
’ except that the right hand side is
a pattern (containing, e.g., *'s, ?'s, and
instances of “[...]”) against which the left-hand operand is
matched. This reduces the need for use of the
switch statement in shell scripts when all
that is really needed is pattern matching.
Strings that begin with ‘0
’ are considered
octal numbers. Null or missing arguments are considered
‘0
’. The results of all expressions are
strings, which represent decimal numbers. It is important to note that no two
components of an expression can appear in the same word; except when adjacent
to components of expressions that are syntactically significant to the parser
(‘&
’,
‘|
’,
‘<
’,
‘>
’,
‘(
’, and
‘)
’), they should be surrounded by
spaces.
Also available in expressions as primitive operands are command executions
enclosed in ‘{
’ and
‘}
’ and file enquiries of the form
-l
name
where l
is one of:
r read access w write access x execute access e existence o ownership z zero size f plain file d directory
0
’. Command executions succeed,
returning true, i.e., ‘1
’, if the
command exits with status 0, otherwise they fail, returning false, i.e.,
‘0
’. If more detailed status information
is required then the command should be executed outside an expression and the
variable status examined.
Control flow¶
The shell contains several commands that can be used to regulate the flow of control in command files (shell scripts) and (in limited but useful ways) from terminal input. These commands all operate by forcing the shell to reread or skip in its input and, because of the implementation, restrict the placement of some of the commands. Theforeach
,
switch
, and
while
statements, as well as the
if-then-else
form of the
if
statement require that the major
keywords appear in a single simple command on an input line as shown below.
If the shell's input is not seekable, the shell buffers up input whenever a loop
is being read and performs seeks in this internal buffer to accomplish the
rereading implied by the loop. (To the extent that this allows, backward
goto's will succeed on non-seekable inputs.)
Built-in commands¶
Built-in commands are executed within the shell. If a built-in command occurs as any component of a pipeline except the last then it is executed in a sub-shell.alias
alias
namealias
name wordlist- The first form prints all aliases. The second form prints the alias for name. The final form assigns the specified wordlist as the alias of name; wordlist is command and filename substituted. name is not allowed to be “alias” or “unalias”.
alloc
- Shows the amount of dynamic memory acquired, broken down into used and free memory. With an argument shows the number of free and used blocks in each size category. The categories start at size 8 and double at each step. This command's output may vary across system types, since systems other than the VAX may use a different memory allocator.
bg
bg %
job ...- Puts the current or specified jobs into the background, continuing them if they were stopped.
break
- Causes execution to resume after the
end
of the nearest enclosingforeach
orwhile
. The remaining commands on the current line are executed. Multi-level breaks are thus possible by writing them all on one line. breaksw
- Causes a break from a
switch
, resuming after theendsw
. case
label:- A label in a
switch
statement as discussed below. cd
cd
namechdir
chdir
name- Change the shell's working directory to directory
name. If no argument is given then change
to the home directory of the user. If
name is not found as a subdirectory of
the current directory (and does not begin with
‘
/
’, ‘./
’ or ‘../
’), then each component of the variable cdpath is checked to see if it has a subdirectory name. Finally, if all else fails but name is a shell variable whose value begins with ‘/
’, then this is tried to see if it is a directory. continue
- Continue execution of the nearest enclosing
while
orforeach
. The rest of the commands on the current line are executed. default
:- Labels the default case in a
switch
statement. The default should come after allcase
labels. dirs
- Prints the directory stack; the top of the stack is at the left, the first directory in the stack being the current directory.
echo
wordlistecho
-n
wordlist- The specified words are written to the shell's standard output, separated
by spaces, and terminated with a newline unless the
-n
option is specified. else
end
endif
endsw
- See the description of the
foreach
,if
,switch
, andwhile
statements below. eval
arg ...- (As in sh(1).) The arguments are read as
input to the shell and the resulting command(s) executed in the context of
the current shell. This is usually used to execute commands generated as
the result of command or variable substitution, since parsing occurs
before these substitutions. See tset(1) for
an example of using
eval
. exec
command- The specified command is executed in place of the current shell.
exit
exit
(expr)- The shell exits either with the value of the
status
variable (first form) or with the value of the specifiedexpr
(second form). fg
fg %
job ...- Brings the current or specified jobs into the foreground, continuing them if they were stopped.
foreach
name (wordlist)- ...
end
- The variable name is successively set to
each member of wordlist and the sequence
of commands between this command and the matching
end
are executed. (Bothforeach
andend
must appear alone on separate lines.) The built-in commandcontinue
may be used to continue the loop prematurely and the built-in commandbreak
to terminate it prematurely. When this command is read from the terminal, the loop is read once prompting with ‘?
’ before any statements in the loop are executed. If you make a mistake typing in a loop at the terminal you can rub it out. glob
wordlist- Like
echo
but no ‘\
’ escapes are recognized and words are delimited by NUL characters in the output. Useful for programs that wish to use the shell to filename expand a list of words. goto
word- The specified word is filename and
command expanded to yield a string of the form
‘
label
’. The shell rewinds its input as much as possible and searches for a line of the form “label:”, possibly preceded by blanks or tabs. Execution continues after the specified line. hashstat
- Print a statistics line showing how effective the internal hash table has
been at locating commands (and avoiding
exec
´s). Anexec
is attempted for each component of the path where the hash function indicates a possible hit, and in each component that does not begin with a ‘/
’. history
history
nhistory
-h
nhistory
-r
n- Displays the history event list; if n is
given, only the n most recent events are
printed. The
-h
option causes the history list to be printed without leading numbers. This format produces files suitable for sourcing using the-h
option tosource
. The-r
option reverses the order of printout to be most recent first instead of oldest first. if
(expr) command- If the specified expression evaluates to true, then the single
command with arguments is executed.
Variable substitution on command happens
early, at the same time it does for the rest of the
if
command. command must be a simple command, not a pipeline, a command list, or a parenthesized command list. Input/output redirection occurs even if expr is false, i.e., when command is not executed (this is a bug). if
(expr)then
- ...
else if
(expr2)then
- ...
else
- ...
endif
- If the specified expr is true then the
commands up to the first
else
are executed; otherwise if expr2 is true then the commands up to the secondelse
are executed, etc. Any number ofelse-if
pairs are possible; only oneendif
is needed. Theelse
part is likewise optional. (The wordselse
andendif
must appear at the beginning of input lines; theif
must appear alone on its input line or after anelse
.) jobs
jobs
-l
- Lists the active jobs; the
-l
option lists process IDs in addition to the normal information. kill %
jobkill
- [] pid
-s
signal_name kill
-sig
pid ...kill
-l
[exit_status]- Sends either the
SIGTERM
(terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in ⟨signal.h⟩, stripped of the prefix “SIG”). The signal names are listed by “kill -l”; if an exit_status is specified, only the corresponding signal name will be written. There is no default; just saying “kill” does not send a signal to the current job. If the signal being sent isSIGTERM
(terminate) orSIGHUP
(hangup), then the job or process will be sent aSIGCONT
(continue) signal as well. limit
limit
resourcelimit
resource maximum-uselimit
-h
limit
-h
resourcelimit
-h
resource maximum-use- Limits the consumption by the current process and each process it creates
to not individually exceed maximum-use on
the specified resource. If no
maximum-use is given, then the current
limit is printed; if no resource is
given, then all limitations are given. If the
-h
flag is given, the hard limits are used instead of the current limits. The hard limits impose a ceiling on the values of the current limits. Only the superuser may raise the hard limits, but a user may lower or raise the current limits within the legal range. Resources controllable currently include:- cputime
- the maximum number of CPU-seconds to be used by each process.
- filesize
- the largest single file (in bytes) that can be created.
- datasize
- the maximum growth of the data+stack region via sbrk(2) beyond the end of the program text.
- stacksize
- the maximum size of the automatically-extended stack region.
- coredumpsize
- the size of the largest core dump (in bytes) that will be created.
- memoryuse
- the maximum size (in bytes) to which a process's resident set size (RSS) may grow.
- memorylocked
- The maximum size (in bytes) which a process may lock into memory using the mlock(2) function.
- maxproc
- The maximum number of simultaneous processes for this user ID.
- openfiles
- The maximum number of simultaneous open files for this user ID.
- vmemoryuse
- the maximum size (in bytes) to which a process's total size may grow.
k
’ or “kilobytes” (1024 bytes); a scale factor of ‘m
’ or “megabytes” may also be used. For cputime the default scale is “seconds”; a scale factor of ‘m
’ for minutes or ‘h
’ for hours, or a time of the form “mm:ss” giving minutes and seconds also may be used. For both resource names and scale factors, unambiguous prefixes of the names suffice. login
- Terminate a login shell, replacing it with an instance of /usr/bin/login. This is one way to log off, included for compatibility with sh(1).
logout
- Terminate a login shell. Especially useful if ignoreeof is set.
nice
nice
+numbernice
commandnice
+number command- The first form sets the scheduling priority for this shell to 4. The
second form sets the priority to the given
number. The final two forms run command
at priority 4 and number respectively.
The greater the number, the less CPU the process will get. The superuser
may specify negative priority by using “nice -number ...”.
command is always executed in a
sub-shell, and the restrictions placed on commands in simple
if
statements apply. nohup
nohup
command- The first form can be used in shell scripts to cause hangups to be ignored
for the remainder of the script. The second form causes the specified
command to be run with hangups ignored. All processes detached with
‘
&
’ are effectivelynohup
´ed. notify
notify %
job ...- Causes the shell to notify the user asynchronously when the status of the current or specified jobs change; normally notification is presented before a prompt. This is automatic if the shell variable notify is set.
onintr
onintr
-
onintr
label- Control the action of the shell on interrupts. The first form restores the
default action of the shell on interrupts, which is to terminate shell
scripts or to return to the terminal command input level. The second form
onintr -
causes all interrupts to be ignored. The final form causes the shell to execute agoto label
when an interrupt is received or a child process terminates because it was interrupted. In any case, if the shell is running detached and interrupts are being ignored, all forms ofonintr
have no meaning and interrupts continue to be ignored by the shell and all invoked commands. Finally,onintr
statements are ignored in the system startup files where interrupts are disabled (/etc/csh.cshrc, /etc/csh.login). popd
popd
+n- Pops the directory stack, returning to the new top directory. With an argument “+n” discards the n´th entry in the stack. The members of the directory stack are numbered from the top starting at 0.
pushd
pushd
namepushd
+n- With no arguments,
pushd
exchanges the top two elements of the directory stack. Given a name argument,pushd
changes to the new directory (alacd
) and pushes the old current working directory (as incwd
) onto the directory stack. With a numeric argument,pushd
rotates the n´th argument of the directory stack around to be the top element and changes to it. The members of the directory stack are numbered from the top starting at 0. rehash
- Causes the internal hash table of the contents of the directories in the
path variable to be recomputed. This is
needed if new commands are added to directories in the
path
while you are logged in. This should only be necessary if you add commands to one of your own directories, or if a systems programmer changes the contents of a system directory. repeat
count command- The specified command, which is subject
to the same restrictions as the command
in the one line
if
statement above, is executed count times. I/O redirections occur exactly once, even if count is 0. set
set
nameset
name=wordset
name[index]=wordset
name=(wordlist)- The first form of the command shows the value of all shell variables. Variables that have other than a single word as their value print as a parenthesized word list. The second form sets name to the null string. The third form sets name to the single word. The fourth form sets the index'th component of name to word; this component must already exist. The final form sets name to the list of words in wordlist. The value is always command and filename expanded. These arguments may be repeated to set multiple values in a single set command. Note however, that variable expansion happens for all arguments before any setting occurs.
setenv
setenv
namesetenv
name value- The first form lists all current environment variables. It is equivalent
to printenv(1). The last form sets the value
of environment variable name to be
value, a single string. The second form
sets name to an empty string. The most
commonly used environment variables
USER
,TERM
, andPATH
are automatically imported to and exported from thecsh
variables user, term, and path; there is no need to usesetenv
for these. shift
shift
variable- The members of
argv
are shifted to the left, discardingargv
[1]. It is an error forargv
not to be set or to have less than one word as value. The second form performs the same function on the specified variable. source
namesource
-h
name- The shell reads commands from name.
source
commands may be nested; if they are nested too deeply the shell may run out of file descriptors. An error in asource
at any level terminates all nestedsource
commands. Normally input duringsource
commands is not placed on the history list; the-h
option causes the commands to be placed on the history list without being executed. stop
stop %
job ...- Stops the current or specified jobs that are executing in the background.
suspend
- Causes the shell to stop in its tracks, much as if it had been sent a stop
signal with
^Z
. This is most often used to stop shells started by su(1). switch
(string)case
str1:- ...
breaksw
- ...
default
:- ...
breaksw
endsw
- Each case label is successively matched against the specified
string, which is first command and
filename expanded. The file metacharacters
‘
*
’, ‘?
’ and “[...]” may be used in the case labels, which are variable expanded. If none of the labels match before the “default” label is found, then the execution begins after the default label. Each case label and the default label must appear at the beginning of a line. The commandbreaksw
causes execution to continue after theendsw
. Otherwise control may fall through case labels and the default label as in C. If no label matches and there is no default, execution continues after theendsw
. time
time
command- With no argument, a summary of time used by this shell and its children is
printed. If arguments are given the specified simple command is timed and
a time summary as described under the
time
variable is printed. If necessary, an extra shell is created to print the time statistic when the command completes. umask
umask
value- The file creation mask is displayed (first form) or set to the specified value (second form). The mask is given in octal. Common values for the mask are 002 giving all access to the group and read and execute access to others or 022 giving all access except write access for users in the group or others.
unalias
pattern- All aliases whose names match the specified pattern are discarded. Thus
all aliases are removed by
unalias *
. It is not an error for nothing to beunalias
ed. unhash
- Use of the internal hash table to speed location of executed programs is disabled.
unlimit
unlimit
resourceunlimit
-h
unlimit
-h
resource- Removes the limitation on resource. If no
resource is specified, then all
resource limitations are removed. If
-h
is given, the corresponding hard limits are removed. Only the superuser may do this. unset
pattern- All variables whose names match the specified pattern are removed. Thus
all variables are removed by
unset *
; this has noticeably distasteful side-effects. It is not an error for nothing to beunset
. unsetenv
pattern- Removes all variables whose names match the specified pattern from the
environment. See also the
setenv
command above and printenv(1). wait
- Wait for all background jobs. If the shell is interactive, then an interrupt can disrupt the wait. After the interrupt, the shell prints names and job numbers of all jobs known to be outstanding.
which
command- Displays the resolved command that will be executed by the shell.
while
(expr)- ...
end
- While the specified expression evaluates to non-zero, the commands between
the
while
and the matchingend
are evaluated.break
andcontinue
may be used to terminate or continue the loop prematurely. (Thewhile
andend
must appear alone on their input lines.) Prompting occurs here the first time through the loop as for theforeach
statement if the input is a terminal. %
job- Brings the specified job into the foreground.
%
job&
- Continues the specified job in the background.
@
@
name= expr@
name[index]= expr- The first form prints the values of all the shell variables. The second
form sets the specified name to the value
of expr. If the expression contains
‘
<
’, ‘>
’, ‘&
’ or ‘|
’ then at least this part of the expression must be placed within ‘(
’ ‘)
’. The third form assigns the value of expr to the index'th argument of name. Both name and its index'th component must already exist. The operators ‘*=
’, ‘+=
’, etc. are available as in C. The space separating the name from the assignment operator is optional. Spaces are, however, mandatory in separating components of expr, which would otherwise be single words. Special postfix ‘++
’ and ‘--
’ operators increment and decrement name respectively; i.e., “@ i++”.
Pre-defined and environment variables¶
The following variables have special meaning to the shell. Of these, argv, cwd, home, path, prompt, shell and status are always set by the shell. Except for cwd and status, this setting occurs only at initialization; these variables will not then be modified unless done explicitly by the user. The shell copies the environment variableUSER
into the variable
user, TERM
into term, and
HOME
into
home, and copies these back into the
environment whenever the normal shell variables are reset. The environment
variable PATH
is likewise handled; it is
not necessary to worry about its setting other than in the file
.cshrc as inferior
csh
processes will import the definition of
path from the environment, and re-export it
if you then change it.
argv
- Set to the arguments to the shell, it is from this variable that positional parameters are substituted; i.e., “$1” is replaced by “$argv[1]”, etc.
cdpath
- Gives a list of alternate directories searched to find subdirectories in
chdir
commands. cwd
- The full pathname of the current directory.
echo
- Set when the
-x
command-line option is given. Causes each command and its arguments to be echoed just before it is executed. For non-built-in commands all expansions occur before echoing. Built-in commands are echoed before command and filename substitution, since these substitutions are then done selectively. filec
- Enable file name completion.
histchars
- Can be given a string value to change the characters used in history
substitution. The first character of its value is used as the history
substitution character, replacing the default character
‘
!
’. The second character of its value replaces the character ‘^
’ in quick substitutions. histfile
- Can be set to the pathname where history is going to be saved/restored.
history
- Can be given a numeric value to control the size of the history list. Any command that has been referenced in this many events will not be discarded. Too large values of history may run the shell out of memory. The last executed command is always saved on the history list.
home
- The home directory of the invoker, initialized from the environment. The filename expansion of “~” refers to this variable.
ignoreeof
- If set the shell ignores end-of-file from input devices which are terminals. This prevents shells from accidentally being killed by control-Ds.
mail
- The files where the shell checks for mail. This checking is done after each command completion that will result in a prompt, if a specified interval has elapsed. The shell says “You have new mail.” if the file exists with an access time not greater than its modify time. If the first word of the value of mail is numeric it specifies a different mail checking interval, in seconds, than the default, which is 10 minutes. If multiple mail files are specified, then the shell says “New mail in name” when there is mail in the file name.
noclobber
- As described in the section on
Input/output,
restrictions are placed on output redirection to ensure that files are not
accidentally destroyed, and that
‘
>>
’ redirections refer to existing files. noglob
- If set, filename expansion is inhibited. This inhibition is most useful in shell scripts that are not dealing with filenames, or after a list of filenames has been obtained and further expansions are not desirable.
nonomatch
- If set, it is not an error for a filename expansion to not match any existing files; instead the primitive pattern is returned. It is still an error for the primitive pattern to be malformed; i.e., “echo [” still gives an error.
notify
- If set, the shell notifies asynchronously of job completions; the default is to present job completions just before printing a prompt.
path
- Each word of the path variable specifies
a directory in which commands are to be sought for execution. A null word
specifies the current directory. If there is no
path variable then only full path names
will execute. The usual search path is “.”,
“/bin”, “/usr/bin”, “/sbin” and
“/usr/sbin”, but this may vary from system to system. For
the superuser the default search path is “/bin”,
“/usr/bin”, “/sbin”, and
“/usr/sbin”. A shell that is given neither the
-c
nor the-t
option will normally hash the contents of the directories in the path variable after reading .cshrc, and each time the path variable is reset. If new commands are added to these directories while the shell is active, it may be necessary to do arehash
or the commands may not be found. prompt
- The string that is printed before each command is read from an interactive
terminal input. If a ‘
!
’ appears in the string it will be replaced by the current event number unless a preceding ‘\
’ is given. Default is “%”, or “#” for the superuser. savehist
- Is given a numeric value to control the number of entries of the history list that are saved in ~/.history when the user logs out. Any command that has been referenced in this many events will be saved. During start up the shell sources ~/.history into the history list enabling history to be saved across logins. Too large values of savehist will slow down the shell during start up. If savehist is just set, the shell will use the value of history.
shell
- The file in which the shell resides. This variable is used in forking shells to interpret files that have execute bits set, but which are not executable by the system. (See the description of Non-built-in command execution below.) Initialized to the (system-dependent) home of the shell.
status
- The status returned by the last command. If it terminated abnormally, then 0200 is added to the status. Built-in commands that fail return exit status 1, all other built-in commands set status to 0.
time
- Controls automatic timing of commands. If set, then any command that takes more than this many CPU seconds will cause a line giving user, system, and real times, and a utilization percentage which is the ratio of user plus system times to real time to be printed when it terminates.
verbose
- Set by the
-v
command-line option, causes the words of each command to be printed after history substitution.
Non-built-in command execution¶
When a command to be executed is found to not be a built-in command the shell attempts to execute the command via execve(2). Each word in the variable path names a directory from which the shell will attempt to execute the command. If it is given neither a-c
nor a
-t
option, the shell will hash the names in
these directories into an internal table so that it will only try an
exec
in a directory if there is a
possibility that the command resides there. This shortcut greatly speeds
command location when many directories are present in the search path. If this
mechanism has been turned off (via unhash
),
or if the shell was given a -c
or
-t
argument, and in any case for each
directory component of path that does not
begin with a ‘/
’, the shell concatenates
with the given command name to form a path name of a file which it then
attempts to execute.
Parenthesized commands are always executed in a sub-shell. Thus
(cd; pwd); pwd
cd; pwd
chdir
from affecting the current shell.
If the file has execute permissions but is not an executable binary to the
system, then it is assumed to be a file containing shell commands and a new
shell is spawned to read it.
If there is an alias for shell
then the words
of the alias will be prepended to the argument list to form the shell command.
The first word of the alias should be the full path name of the shell (e.g.,
“$shell”). Note that this is a special, late occurring, case of
alias
substitution, and only allows words
to be prepended to the argument list without change.
Signal handling¶
The shell normally ignoresSIGQUIT
signals.
Jobs running detached (either by &
or
the bg
or %...
&
commands) are immune to signals generated from the keyboard,
including hangups. Other signals have the values which the shell inherited
from its parent. The shell's handling of interrupts and terminate signals in
shell scripts can be controlled by onintr
.
Login shells catch the SIGTERM
(terminate)
signal; otherwise this signal is passed on to children from the state in the
shell's parent. Interrupts are not allowed when a login shell is reading the
file .logout.
LIMITATIONS¶
Word lengths - Words can be no longer than 1024 characters. The number of arguments to a command that involves filename expansion is limited to 1/6th the number of characters allowed in an argument list. Command substitutions may substitute no more characters than are allowed in an argument list. To detect looping, the shell restricts the number ofalias
substitutions on a single line to 20.
FILES¶
- ~/.cshrc
- read at beginning of execution by each shell
- ~/.login
- read by login shell, after .cshrc at login
- ~/.logout
- read by login shell, at logout
- /bin/sh
- standard shell, for shell scripts not starting with a
‘
#
’ - /tmp/sh.*
- temporary file for ‘
<<
’ - /etc/passwd
- source of home directories for “~name”
SEE ALSO¶
sh(1), access(2), execve(2), fork(2), pipe(2), setrlimit(2), umask(2), wait(2), killpg(3), sigvec(3), tty(4), a.out(5), environ(7), script(7)HISTORY¶
csh
appeared in 3BSD.
It was a first implementation of a command language interpreter incorporating
a history mechanism (see
History
substitutions), job control facilities (see
Jobs), interactive file name and
user name completion (see
File name
completion), and a C-like syntax. There are now many shells that also have
these mechanisms, plus a few more (and maybe some bugs too), which are
available through the usenet.
AUTHORS¶
William Joy. Job control and directory stack features first implemented by J.E. Kulp of IIASA, Laxenburg, Austria, with different syntax than that used now. File name completion code written by Ken Greer, HP Labs. Eight-bit implementation Christos S. Zoulas, Cornell University.BUGS¶
When a command is restarted from a stop, the shell prints the directory it started in if this is different from the current directory; this can be misleading (i.e., wrong) as the job may have changed directories internally. Shell built-in functions are not stoppable/restartable. Command sequences of the form “a ; b ; c” are also not handled gracefully when stopping is attempted. If you suspend ‘b
’, the
shell will immediately execute ‘c
’. This
is especially noticeable if this expansion results from an alias. It suffices
to place the sequence of commands in ()'s to force it to a sub-shell; i.e.,
“(a ; b ; c)”.
Control over tty output after processes are started is primitive; perhaps this
will inspire someone to work on a good virtual terminal interface. In a
virtual terminal interface much more interesting things could be done with
output control.
Alias substitution is most often used to clumsily simulate shell procedures;
shell procedures should be provided instead of aliases.
Commands within loops, prompted for by
‘?
’, are not placed on the
history
list. Control structure should be
parsed instead of being recognized as built-in commands. This would allow
control commands to be placed anywhere, to be combined with
‘|
’, and to be used with
‘&
’ and
‘;
’ metasyntax.
It should be possible to use the ‘:
’
modifiers on the output of command substitutions.
The way the filec facility is implemented is
ugly and expensive.May 2, 2011 | Debian |