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OLDCSH(1) UNIX Programmer's Manual OLDCSH(1)

NAME
oldcsh - a shell (command interpreter) with C-like syntax

SYNOPSIS
oldcsh [ -cefinstvVxX ] [ arg ... ]

DESCRIPTION
_O_l_d_c_s_h is a command language interpreter similar to _c_s_h(1)
but without its process control facilities. It begins by
executing commands from the file `.cshrc' in the _h_o_m_e direc-
tory of the invoker. If this is a login shell then it also
executes commands from the file `.login' there. In the nor-
mal case, the shell will then 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 then repeatedly performs the following actions: a
line of command input is read and broken into _w_o_r_d_s. This
sequence of words is placed on the command history list and
then parsed. Finally each command in the current line is
executed.

When a login shell terminates it executes commands from the
file `.logout' in the users home directory.

Lexical structure

The shell splits input lines into words at blanks and tabs
with the following exceptions. The characters `&' `|' `;'
`<' `>' `(' `)' form separate words. If doubled in `&&',
`||', `<<' or `>>' these pairs form single words. These
parser metacharacters may be made part of other words, or
prevented their special meaning, by preceding them with `\'.
A newline preceded by a `\' is equivalent to a blank.

In addition 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 subsequently. Within pairs of `' or `"' charac-
ters a newline preceded by a `\' gives a true newline char-
acter.

When the shell's input is not a terminal, the character `#'
introduces a comment which continues to the end of the input
line. It is prevented this special meaning when preceded by
`\' and in quotations using ``', `'', and `"'.

Commands

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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 pipe-
lines may be separated by `;', and are then executed sequen-
tially. A sequence of pipelines may be executed without
waiting for it to terminate by following it with an `&'.
Such a sequence is automatically prevented from being ter-
minated by a hangup signal; the _n_o_h_u_p command need not be
used.

Any of the above may be placed in `(' `)' to form a simple
command (which may be a component of a pipeline, etc.) It is
also possible to separate pipelines with `||' or `&&' indi-
cating, as in the C language, that the second is to be exe-
cuted only if the first fails or succeeds respectively. (See
_E_x_p_r_e_s_s_i_o_n_s.)

Substitutions

We now describe the various transformations the shell per-
forms on the input in the order in which they occur.

History substitutions

History substitutions can be used to reintroduce sequences
of words from previous commands, possibly performing modifi-
cations on these words. Thus history substitutions provide
a generalization of a _r_e_d_o function.

History substitutions begin with the character `!' and may
begin anywhere in the input stream if a history substitution
is not already in progress. This `!' may be preceded by an
`\' to prevent its special meaning; a `!' 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 which contains history substitution is echoed
on the terminal before it is executed as it could have been
typed without history substitution.

Commands input from the terminal which consist of one or
more words are saved on the history list, the size of which
is controlled by the _h_i_s_t_o_r_y variable. The previous command
is always retained. Commands are numbered sequentially from
1.

For definiteness, consider the following output from the
history command:

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9 write michael
10 ex write.c
11 cat oldwrite.c
12 diff *write.c

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 _p_r_o_m_p_t by placing an
`!' 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 `!w' 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 modification, simply rein-
troduce the words of the specified events, each separated by
a single blank. As a special case `!!' refers to the previ-
ous command; thus `!!' alone is essentially a _r_e_d_o. The form
`!#' references the current command (the one being typed
in). It allows a word to be selected from further left in
the line, to avoid retyping a long name, as in `!#:1'.

To select words from an event we can follow the event
specification by a `:' and a designator for the desired
words. The words of a 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 `$'

The `:' separating the event specification from the word
designator can be omitted if the argument selector begins
with a `^|', `$', `*' `-' or `%'. After the optional word
designator can be placed a sequence of modifiers, each pre-
ceded 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.
s/_l/_r/ Substitute _l for _r
t Remove all leading pathname components, leaving the tail.
& Repeat the previous substitution.
g Apply the change globally, prefixing the above, e.g. `g&'.

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p Print the new command 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.

Unless preceded by a `g' the modification is applied only to
the first modifiable word. In any case it is an error for
no word to be applicable.

The left hand side of substitutions are not regular expres-
sions in the sense of the editors, but rather 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 `\' quotes `&' also. A null _l uses the
previous string either from a _l or from a contextual scan
string _s in `!?_s?'. The trailing delimiter in the substitu-
tion 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 specifica-
tion, e.g. `!$'. In this case the reference is to the pre-
vious command unless a previous history reference occurred
on the same line in which case this form repeats the previ-
ous reference. Thus `!?foo?^| !$' 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 short-
hand 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 char-
acters which follow. Thus, after `ls -ld ~paul' we might do
`!{l}a' to do `ls -ld ~paula', while `!la' would look for a
command starting `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 any further interpretation.
Strings enclosed in `"' are yet variable and command
expanded as described below.

In both cases the resulting text becomes (all or part of) a
single word; only in one special case (see _C_o_m_m_a_n_d _S_u_b_s_t_i_t_u_-
_t_i_o_n below) does a `"' quoted string yield parts of more
than one word; `' quoted strings never do.

Alias substitution

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The shell maintains a list of aliases which can be esta-
blished, displayed and modified by the _a_l_i_a_s and _u_n_a_l_i_a_s
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 which 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 which _p_r'_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 _a_r_g_v variable is an image of the shell's argument list,
and words of this variable's value are referred to in spe-
cial ways.

The values of variables may be displayed and changed by
using the _s_e_t and _u_n_s_e_t 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 _v_e_r_b_o_s_e variable is a toggle which causes
command input to be echoed. The setting of this variable
results from the -v command line option.

Other operations treat variables numerically. The `@' com-
mand permits numeric calculations to be performed and the
result assigned to a variable. Variable values are, how-
ever, always represented as (zero or more) strings. For the
purposes of numeric operations, the null string is con-
sidered to be zero, and the second and subsequent words of

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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 `"'s where it
always occurs, and within `'s where it never occurs.
Strings quoted by ``' are interpreted later (see _C_o_m_m_a_n_d
_s_u_b_s_t_i_t_u_t_i_o_n below) so `$' substitution does not occur there
until later, if at all. A `$' is passed unchanged if fol-
lowed 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 sin-
gle 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.

The following metasequences are provided for introducing
variable values into the shell input. Except as noted, it
is an error to reference a variable which is not set.

$name
${name}
Are replaced by the words of the value of variable
_n_a_m_e, each separated by a blank. Braces insulate _n_a_m_e
from following characters which would otherwise be part
of it. Shell variables have names consisting of up to
20 letters, digits, and underscores.

If _n_a_m_e is not a shell variable, but is set in the environ-
ment, then that value is returned (but : modifiers and the
other forms given below are not available in this case).

$name[selector]
${name[selector]}
May be used to select only some of the words from the
value of _n_a_m_e. The selector is subjected to `$' substi-
tution and may consist of a single number or two
numbers separated by a `-'. The first word of a

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variables value is numbered `1'. If the first number
of a range is omitted it defaults to `1'. If the last
member 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 omit-
ted or in range.

$#name
${#name}
Gives the number of words in the variable. This is
useful for later use in a `[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[*]'.

The modifiers `: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 modif-
iers must appear within the braces. The current implementa-
tion 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 know,
`0' if it is not.

$$
Substitute the (decimal) process number of the (parent)
shell.

Command and filename substitution

The remaining substitutions, command and filename substitu-
tion, are applied selectively to the arguments of builtin
commands. This means that portions of expressions which are
not evaluated are not subjected to these expansions. For

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commands which 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 per-
formed, and in a child of the main shell.

Command substitution

Command substitution is indicated 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 replacing the original
string. Within `"'s, 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 substitu-
tion to yield only part of a word, even if the command out-
puts 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 `glob-
bing'. This word is then regarded as a pattern, and
replaced with an alphabetically sorted list of file names
which 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 pat-
tern 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.

The character `~' at the beginning of a filename is used to
refer to home directories. Standing alone, i.e. `~' it
expands to the invokers home directory as reflected in the
value of the variable _h_o_m_e. When followed by a name consist-
ing of letters, digits and `-' characters the shell searches
for a user with that name and substitutes their home direc-
tory; 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
appears not at the beginning of a word, it is left

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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' whether or not these files exist
without any 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 matching `*box'.) As a spe-
cial case `{', `}' and `{}' are passed undisturbed.

Input/output

The standard input and standard output of a command may be
redirected with the following syntax:

< name
Open file _n_a_m_e (which is first variable, command and
filename expanded) as the standard input.

<< word
Read the shell input up to a line which is identical to
_w_o_r_d. _W_o_r_d is not subjected to variable, filename or
command substitution, and each input line is compared
to _w_o_r_d before any substitutions are done on this input
line. Unless a quoting `\', `"', `'' or ``' appears in
_w_o_r_d variable and command substitution is performed on
the intervening lines, allowing `\' to quote `$', `\'
and ``'. Commands which 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 which is given to
the command as standard input.

> name
>! name
>& name
>&! name
The file _n_a_m_e is used as standard output. If the file
does not exist then it is created; if the file exists,
its is truncated, its previous contents being lost.

If the variable _n_o_c_l_o_b_b_e_r is set, then the file must
not exist or be a character special file (e.g. a termi-
nal or `/dev/null') or an error results. This helps
prevent accidental destruction of files. In this case
the `!' forms can be used and suppress this check.

The forms involving `&' route the diagnostic output

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into the specified file as well as the standard output.
_N_a_m_e is expanded in the same way as `<' input filenames
are.

>> name
>>& name
>>! name
>>&! name
Uses file _n_a_m_e as standard output like `>' but places
output at the end of the file. If the variable
_n_o_c_l_o_b_b_e_r is set, then it is an error for the file not
to exist unless one of the `!' forms is given. Other-
wise similar to `>'.

If a command is run detached (followed by `&') then the
default standard input for the command is the empty file
`/dev/null'. Otherwise the command receives the environment
in which the shell was invoked as modified by the input-
output parameters and the presence of the command in a pipe-
line. Thus, unlike some previous shells, commands run from
a file of shell commands have no access to the text of the
commands by default; rather they receive the original stan-
dard input of the shell. The `<<' 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.

Diagnostic output may be directed through a pipe with the
standard output. Simply use the form `|&' rather than just
`|'.

Expressions

A number of the builtin commands (to be described subse-
quently) take expressions, in which the operators are simi-
lar to those of C, with the same precedence. These expres-
sions appear in the @, _e_x_i_t, _i_f, and _w_h_i_l_e 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 oth-
ers operate on numbers. Strings which begin with `0' are
considered octal numbers. Null or missing arguments are
considered `0'. The result 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

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which are syntactically significant to the parser (`&' `|'
`<' `>' `(' `)') they should be surrounded by spaces.

Also available in expressions as primitive operands are com-
mand 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

The specified name is command and filename expanded and then
tested to see if it has the specified relationship to the
real user. If the file does not exist or is inaccessible
then all enquiries return false, i.e. `0'. Command execu-
tions 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 of an expression
and the variable _s_t_a_t_u_s examined.

Control flow

The shell contains a number of commands which 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, due to the implementation,
restrict the placement of some of the commands.

The _f_o_r_e_a_c_h, _s_w_i_t_c_h, and _w_h_i_l_e statements, as well as the
_i_f-_t_h_e_n-_e_l_s_e form of the _i_f 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.)

Builtin commands

Builtin commands are executed within the shell. If a buil-
tin command occurs as any component of a pipeline except the
last then it is executed in a subshell.

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alias
alias name
alias name wordlist
The first form prints all aliases. The second form
prints the alias for name. The final form assigns the
specified _w_o_r_d_l_i_s_t as the alias of _n_a_m_e; _w_o_r_d_l_i_s_t is
command and filename substituted. _N_a_m_e is not allowed
to be _a_l_i_a_s or _u_n_a_l_i_a_s

alloc
Shows the amount of dynamic core in use, broken down
into used and free core, and address of the last loca-
tion in the heap. With an argument shows each used and
free block on the internal dynamic memory chain indi-
cating its address, size, and whether it is used or
free. This is a debugging command and may not work in
production versions of the shell; it requires a modi-
fied version of the system memory allocator.

break
Causes execution to resume after the _e_n_d of the nearest
enclosing _f_o_r_e_a_c_h or _w_h_i_l_e. 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 _s_w_i_t_c_h, resuming after the _e_n_d_s_w.

case label:
A label in a _s_w_i_t_c_h statement as discussed below.

cd
cd name
chdir
chdir name
Change the shells working directory to directory _n_a_m_e.
If no argument is given then change to the home direc-
tory of the user.

If _n_a_m_e is not found as a subdirectory of the current direc-
tory (and does not begin with `/', `./', or `../'), then
each component of the variable _c_d_p_a_t_h is checked to see if
it has a subdirectory _n_a_m_e. Finally, if all else fails but
_n_a_m_e 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 _w_h_i_l_e or
_f_o_r_e_a_c_h. The rest of the commands on the current line
are executed.

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default:
Labels the default case in a _s_w_i_t_c_h statement. The
default should come after all _c_a_s_e labels.

echo wordlist
The specified words are written to the shells standard
output. A `\c' causes the echo to complete without
printing a newline, akin to the `\c' in _n_r_o_f_f(1). A
`\n' in wordlist causes a newline to be printed. Oth-
erwise the words are echoed, separated by spaces.

else
end
endif
endsw
See the description of the _f_o_r_e_a_c_h, _i_f, _s_w_i_t_c_h, and
_w_h_i_l_e statements below.

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 _s_t_a_t_u_s
variable (first form) or with the value of the speci-
fied _e_x_p_r (second form).

foreach name (wordlist)
...
end
The variable _n_a_m_e is successively set to each member of
_w_o_r_d_l_i_s_t and the sequence of commands between this com-
mand and the matching _e_n_d are executed. (Both _f_o_r_e_a_c_h
and _e_n_d must appear alone on separate lines.)

The builtin command _c_o_n_t_i_n_u_e may be used to continue
the loop prematurely and the builtin command _b_r_e_a_k to
terminate it prematurely. When this command is read
from the terminal, the loop is read up once prompting
with `?' before any statements in the loop are exe-
cuted. If you make a mistake typing in a loop at the
terminal you can rub it out.

glob wordlist
Like _e_c_h_o but no `\' escapes are recognized and words
are delimited by null characters in the output. Useful
for programs which wish to use the shell to filename
expand a list of words.

goto word
The specified _w_o_r_d is filename and command expanded to

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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 indicating how effective the
internal hash table has been at locating commands (and
avoiding _e_x_e_c's). An _e_x_e_c is attempted for each com-
ponent of the _p_a_t_h where the hash function indicates a
possible hit, and in each component which does not
begin with a ``/''.

history
Displays the history event list.

if (expr) command
If the specified expression evaluates true, then the
single _c_o_m_m_a_n_d with arguments is executed. Variable
substitution on _c_o_m_m_a_n_d happens early, at the same time
it does for the rest of the _i_f command. _C_o_m_m_a_n_d must
be a simple command, not a pipeline, a command list, or
a parenthesized command list. Input/output redirection
occurs even if _e_x_p_r is false, when command is not exe-
cuted (this is a bug).

if (expr) then
...
else if (expr2) then
...
else
...
endif
If the specified _e_x_p_r is true then the commands to the
first _e_l_s_e are executed; else if _e_x_p_r_2 is true then the
commands to the second else are executed, etc. Any
number of _e_l_s_e-_i_f pairs are possible; only one _e_n_d_i_f is
needed. The _e_l_s_e part is likewise optional. (The
words _e_l_s_e and _e_n_d_i_f must appear at the beginning of
input lines; the _i_f must appear alone on its input line
or after an _e_l_s_e.)

login
Terminate a login shell, replacing it with an instance
of /bin/login. This is one way to log off, included for
compatibility with /bin/sh.

logout
Terminate a login shell. Especially useful if
_i_g_n_o_r_e_e_o_f is set.

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nice
nice +number
nice command
nice +number command
The first form sets the _n_i_c_e for this shell to 4. The
second form sets the _n_i_c_e to the given number. The
final two forms run command at priority 4 and _n_u_m_b_e_r
respectively. The super-user may specify negative
niceness by using `nice -number ...'. Command is
always executed in a sub-shell, and the restrictions
place on commands in simple _i_f 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. On the Computer Center systems
at UC Berkeley, this also _s_u_b_m_i_t_s the process. Unless
the shell is running detached, _n_o_h_u_p has no effect.
All processes detached with ``&'' are automatically
_n_o_h_u_p'_e_d. (Thus, _n_o_h_u_p is not really needed.)

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 a `goto
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 of _o_n_i_n_t_r have
no meaning and interrupts continue to be ignored by the
shell and all invoked commands.

rehash
Causes the internal hash table of the contents of the
directories in the _p_a_t_h variable to be recomputed.
This is needed if new commands are added to directories
in the _p_a_t_h 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 one of the system directories.

repeat count command
The specified _c_o_m_m_a_n_d which is subject to the same res-
trictions as the _c_o_m_m_a_n_d in the one line _i_f statement

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above, is executed _c_o_u_n_t times. I/O redirections
occurs exactly once, even if _c_o_u_n_t is 0.

set
set name
set name=word
set name[index]=word
set name=(wordlist)
The first form of the command shows the value of all
shell variables. Variables which have other than a
single word as value print as a parenthesized word
list. The second form sets _n_a_m_e to the null string.
The third form sets _n_a_m_e to the single _w_o_r_d. The fourth
form sets the _i_n_d_e_x'_t_h component of name to word; this
component must already exist. The final form sets _n_a_m_e
to the list of words in _w_o_r_d_l_i_s_t. In all cases the
value is 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 name value
(Version 7 systems only.) Sets the value of environment
variable _n_a_m_e to be _v_a_l_u_e, a single string. Useful
environment variables are `TERM' the type of your ter-
minal and `SHELL' the shell you are using.

shift
shift variable
The members of _a_r_g_v are shifted to the left, discarding
_a_r_g_v[_1]. It is an error for _a_r_g_v not to be set or to
have less than one word as value. The second form per-
forms the same function on the specified variable.

source name
The shell reads commands from _n_a_m_e. _S_o_u_r_c_e commands may
be nested; if they are nested too deeply the shell may
run out of file descriptors. An error in a _s_o_u_r_c_e at
any level terminates all nested _s_o_u_r_c_e commands. Input
during _s_o_u_r_c_e commands is never placed on the history
list.

switch (string)
case str1:
...
breaksw
...
default:
...

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breaksw
endsw
Each case label is successively matched, against the
specified _s_t_r_i_n_g 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 a
`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 command _b_r_e_a_k_s_w causes execution to continue after
the _e_n_d_s_w. Otherwise control may fall through case
labels and default labels as in C. If no label matches
and there is no default, execution continues after the
_e_n_d_s_w.

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 sum-
mary as described under the _t_i_m_e 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 no
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 be _u_n_a_l_i_a_s_e_d.

unhash
Use of the internal hash table to speed location of
executed programs is disabled.

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 be _u_n_s_e_t.

wait
All child processes are waited for. It the shell is
interactive, then an interrupt can disrupt the wait, at

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which time the shell prints names and process numbers
of all children known to be outstanding.

while (expr)
...
end
While the specified expression evaluates non-zero, the
commands between the _w_h_i_l_e and the matching end are
evaluated. _B_r_e_a_k and _c_o_n_t_i_n_u_e may be used to terminate
or continue the loop prematurely. (The _w_h_i_l_e and _e_n_d
must appear alone on their input lines.) Prompting
occurs here the first time through the loop as for the
_f_o_r_e_a_c_h statement if the input is a terminal.

@
@ name = expr
@ name[index] = expr
The first form prints the values of all the shell vari-
ables. The second form sets the specified _n_a_m_e to the
value of _e_x_p_r. If the expression contains `<', `>', `&'
or `|' then at least this part of the expression must
be placed within `(' `)'. The third form assigns the
value of _e_x_p_r to the _i_n_d_e_x'_t_h argument of _n_a_m_e. Both
_n_a_m_e and its _i_n_d_e_x'_t_h 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 _e_x_p_r which would otherwise
be single words.

Special postfix `++' and `--' operators increment and
decrement _n_a_m_e respectively, i.e. `@ i++'.

Pre-defined variables

The following variables have special meaning to the shell.
Of these, _a_r_g_v, _c_h_i_l_d, _h_o_m_e, _p_a_t_h, _p_r_o_m_p_t, _s_h_e_l_l and _s_t_a_t_u_s
are always set by the shell. Except for _c_h_i_l_d and _s_t_a_t_u_s
this setting occurs only at initialization; these variables
will not then be modified unless this is done explicitly by
the user.

The shell copies the environment variable PATH into the
variable _p_a_t_h, and copies the value back into the environ-
ment whenever _p_a_t_h is set. Thus is is not necessary to
worry about its setting other than in the file ._c_s_h_r_c as
inferior _o_l_d_c_s_h processes will import the definition of _p_a_t_h
from the environment. (It could be set once in the ._l_o_g_i_n
except that commands through _n_e_t(1) would not see the defin-
ition.)

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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 _c_h_d_i_r com-
mands.

child The process number printed when the last com-
mand was forked with `&'. This variable is
_u_n_s_e_t when this process terminates.

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-
builtin commands all expansions occur before
echoing. Builtin commands are echoed before
command and filename substitution, since
these substitutions are then done selec-
tively.

histchars Can be assigned a two character string. The
first character is used as a history charac-
ter in place of ``!'', the second character
is used in place of the ``^'' substitution
mechanism. For example, ``set
histchars=",;"'' will cause the history char-
acters to be comma and semicolon.

history Can be given a numeric value to control the
size of the history list. Any command which
has been referenced in this many events will
not be discarded. Too large values of _h_i_s_-
_t_o_r_y 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, initial-
ized 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-D's.

mail The files where the shell checks for mail.
This is done after each command completion
which will result in a prompt, if a specified
interval has elapsed. The shell says `You
have new mail.' if the file exists with an

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access time not greater than its modify time.

If the first word of the value of _m_a_i_l is
numeric it specifies a different mail check-
ing interval, in seconds, than the default,
which is 10 minutes.

If multiple mail files are specified, then
the shell says `New mail in _n_a_m_e' when there
is mail in the file _n_a_m_e.

noclobber As described in the section on _I_n_p_u_t/_o_u_t_p_u_t,
restrictions are placed on output redirection
to insure that files are not accidentally
destroyed, and that `>>' redirections refer
to existing files.

noglob If set, filename expansion is inhibited.
This is most useful in shell scripts which
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;
rather the primitive pattern is returned. It
is still an error for the primitive pattern
to be malformed, i.e. `echo [' still gives
an error.

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 _p_a_t_h vari-
able then only full path names will execute.
The usual search path is `.', `/bin' and
`/usr/bin', but this may vary from system to
system. For the super-user the default
search path is `/etc', `/bin' and `/usr/bin'.
A shell which is given neither the -c nor the
-t option will normally hash the contents of
the directories in the _p_a_t_h variable after
reading ._c_s_h_r_c, and each time the _p_a_t_h vari-
able is reset. If new commands are added to
these directories while the shell is active,
it may be necessary to give the _r_e_h_a_s_h or the
commands may not be found.

prompt The string which is printed before each com-
mand is read from an interactive terminal
input. If a `!' appears in the string it
will be replaced by the current event number

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unless a preceding `\' is given. Default is
`% ', or `# ' for the super-user.

shell The file in which the shell resides. This is
used in forking shells to interpret files
which have execute bits set, but which are
not executable by the system. (See the
description of _N_o_n-_b_u_i_l_t_i_n _C_o_m_m_a_n_d _E_x_e_c_u_t_i_o_n
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. Builtin commands which fail
return exit status `1', all other builtin
commands set status `0'.

time Controls automatic timing of commands. If
set, then any command which takes more than
this many cpu seconds will cause a line giv-
ing user, system, and real times and a utili-
zation 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-builtin command execution

When a command to be executed is found to not be a builtin
command the shell attempts to execute the command via
_e_x_e_c_v_e(2). Each word in the variable _p_a_t_h 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 _e_x_e_c in a directory if there is
a possibility that the command resides there. This greatly
speeds command location when a large number of directories
are present in the search path. If this mechanism has been
turned off (via _u_n_h_a_s_h), or if the shell was given a -c or
-t argument, and in any case for each directory component of
_p_a_t_h which does not begin with a ``/'', the shell concaten-
ates 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 subshell.
Thus `(cd ; pwd) ; pwd' prints the _h_o_m_e directory; leaving
you where you were (printing this after the home directory),
while `cd ; pwd' leaves you in the _h_o_m_e directory.
Parenthesized commands are most often used to prevent _c_h_d_i_r

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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 con-
taining shell commands an a new shell is spawned to read it.

If there is an _a_l_i_a_s for _s_h_e_l_l then the words of the alias
will be prepended to the argument list to form the shell
command. The first word of the _a_l_i_a_s should be the full
path name of the shell (e.g. `$shell'). Note that this is a
special, late occurring, case of _a_l_i_a_s substitution, and
only allows words to be prepended to the argument list
without modification.

Argument list processing

If argument 0 to the shell is `-' then this is a login
shell. The flag arguments are interpreted as follows:

-c Commands are read from the (single) following argument
which must be present. Any remaining arguments are
placed in _a_r_g_v.

-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 invokers home directory.

-i The shell is interactive and prompts for its top-level
input, even if it appears to not be a terminal. Shells
are interactive without this option if their inputs and
outputs are terminals.

-n Commands are parsed, but not executed. This may aid in
syntactic checking of shell scripts.

-s Command input is taken from the standard input.

-t A single line of input is read and executed. A `\' may
be used to escape the newline at the end of this line
and continue onto another line.

-v Causes the _v_e_r_b_o_s_e variable to be set, with the effect
that command input is echoed after history substitu-
tion.

-x Causes the _e_c_h_o variable to be set, so that commands
are echoed immediately before execution.

-V Causes the _v_e_r_b_o_s_e variable to be set even before

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`.cshrc' is executed.

-X Is to -x as -V is to -v.

After processing of flag arguments if arguments remain but
none of the -c, -i, -s, or -t options was 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 `#', i.e. if the script does not start
with a comment. Remaining arguments initialize the variable
_a_r_g_v.

Signal handling

The shell normally ignores _q_u_i_t signals. The _i_n_t_e_r_r_u_p_t and
_q_u_i_t signals are ignored for an invoked command if the com-
mand is followed by `&'; otherwise the signals have the
values which the shell inherited from its parent. The
shells handling of interrupts can be controlled by _o_n_i_n_t_r.
Login shells catch the _t_e_r_m_i_n_a_t_e signal; otherwise this sig-
nal is passed on to children from the state in the shell's
parent. In no case are interrupts allowed when a login
shell is reading the file `.logout'.

AUTHOR
William Joy

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 `<<'.
/dev/null Source of empty file.
/etc/passwd Source of home directories for `~name'.

LIMITATIONS
Words can be no longer than 1024 characters. The number of
characters in an argument varies from system to system.
Early version 6 systems typically have 512 character limits
while later version 6 and version 7 systems have 5120 char-
acter limits. The number of arguments to a command which
involves filename expansion is limited to 1/8'th the number
of characters allowed in an argument list. Also command
substitutions may substitute no more characters than are
allowed in an argument list.

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To detect looping, the shell restricts the number of _a_l_i_a_s
substitutions on a single line to 20.

SEE ALSO
access(2), execve(2), fork(2), pipe(2), signal(2), umask(2),
wait(2), exec(3), a.out(5), environ(5), `An introduction to
the C shell'

BUGS
Control structure should be parsed rather than being recog-
nized as built-in commands. This would allow control com-
mands to be placed anywhere, to be combined with `|', and to
be used with `&' and `;' metasyntax.

Commands within loops, prompted for by `?', are not placed
in the _h_i_s_t_o_r_y list.

It should be possible to use the `:' modifiers on the output
of command substitutions. All and more than one `:' modif-
ier should be allowed on `$' substitutions.

Some commands should not touch _s_t_a_t_u_s or it may be so tran-
sient as to be almost useless. Oring in 0200 to _s_t_a_t_u_s on
abnormal termination is a kludge.

In order to be able to recover from failing _e_x_e_c commands on
version 6 systems, the new command inherits several open
files other than the normal standard input and output and
diagnostic output. If the input and output are redirected
and the new command does not close these files, some files
may be held open unnecessarily.

There are a number of bugs associated with the
importing/exporting of the PATH. For example, directories
in the path using the ~ syntax are not expanded in the PATH.
Unusual paths, such as (), can cause oldcsh to core dump.

This version of _o_l_d_c_s_h does not support or use the process
control features of the 4th Berkeley Distribution. It con-
tains a number of known bugs which have been fixed in the
process control version.

Printed 7/25/83 24