MASH(1) MASH(1)
NAME
mash - programmable shell
SYNOPSIS
mash [ -denx ][ -ccommand ] [ file [ arg ... ]]
DESCRIPTION
Mash is an older alternative to the original Inferno shell
(now tiny(1)). Mash is a programmable shell that also allows
the definition of simple dependency rules, resembling those
of Unix make. It executes commands read from standard input
or a file or, with the -c flag, from mash's argument list.
Its syntax and semantics are similar to that of Plan 9's rc.
Invocation
If mash is started with no arguments it reads commands from
standard input. Otherwise its first non-flag argument is the
name of a file from which to read commands (but see -c
below). Subsequent arguments become the initial value of
$args. Mash accepts the following command-line flags.
-c string Commands are read from string.
-d Dump parsed commands before execution.
-e Fail if a top level command does.
-n Parse but do not execute.
-x Print each simple command before executing it.
If invoked without arguments mash first runs the commands
found in /lib/mashinit.
Command Lines
Each command is terminated with an ampersand or a semicolon
(& or ;). When reading from /dev/cons a newline not escaped
with a backslash (\) is treated as a semicolon. Mash does
not wait for a command followed by & to finish executing
before starting the following command.
A number-sign (#) and any following characters up to (but
not including) the next newline are ignored, except in quo-
tation marks.
Simple Commands
A simple command is a sequence of words interspersed with
I/O redirections. If the first word is the name of a mash
function or of one of mash's built-in commands, it is exe-
cuted by mash. Otherwise, if the name starts with a slash
(/), it must be the path name of a Dis file to be loaded and
executed. Names containing no initial slash are searched for
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MASH(1) MASH(1)
in the current directory and then in /dis. The .dis exten-
sion need not be supplied.
The keywords are
case else fn for hd if in len rescue tl while
Words and Variables
A number of constructions may be used where mash's syntax
requires a word to appear. In many cases a construction's
value will be a list of strings rather than a single string.
The simplest kind of word is the unquoted word: a sequence
of one or more characters none of which is a blank, tab,
newline, or any of the following:
# : ; ! ~ @ & | ^ $ = " ` ' { } ( ) < >
An unquoted word that contains any of the characters *, ?
or [ is a pattern for matching against file names. The char-
acter * matches any sequence of characters, ? matches any
single character, and [ class ] matches any character in the
class. The class may also contain pairs of characters sepa-
rated by -, standing for all characters lexically between
the two. The character / must appear explicitly in a pat-
tern. A pattern is replaced by a list of words, one for each
path name matched, except that a pattern matching no names
is not replaced by the empty list, but rather stands for
itself. Pattern matching is done after all other operations.
Thus,
x=/tmp; echo $x^/*.c;
matches /tmp/*.c, rather than matching /*.c and then prefix-
ing /tmp.
A quoted word is a sequence of characters surrounded by sin-
gle quotes ('). A single quote is escaped with a backslash.
Each of the following is a word.
$identifier
The identifier after the $ is the name of a variable
whose value is substituted. Variable values are lists
of strings. It is an error if the named variable has
never been assigned a value.
$number
See the description of rules for the mash-make(1) buil-
tin.
$"identifier
The value is a single string containing the components
of the named variable separated by spaces.
`{commands}
mash executes the commands and reads the standard out-
put, splitting it into a list of words, using the
whitespace characters (space, tab, newline and carriage
return) as separators.
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MASH(1) MASH(1)
"{commands}
mash executes the commands and reads the standard out-
put, splitting it into a list of words, using the
whitespace characters (space, tab, newline and carriage
return) as separators.
<{commands}
>{commands}
The commands are executed asynchronously with their
standard output or standard input connected to a pipe.
The value of the word is the name of a file referring
to the other end of the pipe. This allows the construc-
tion of non-linear pipelines. For example, the follow-
ing runs two commands old and new and uses cmp to com-
pare their outputs
cmp <{old} <{new};
(expr)
mash evaluates expr as an expression. The value is a
(possibly null) list of words. Expressions are
described in detail below.
word^word
The ^ operator concatenates its two operands. If either
operand is a singleton, the concatenation is distribu-
tive. Otherwise the lists are concatenated pairwise.
Free Carets
In most circumstances, mash will insert the ^ operator auto-
matically between words that are not separated by white
space. Whenever one of $ 'or ` (dollar, single quote or back
quote) follows a quoted or unquoted word or an unquoted word
follows a quoted word with no intervening blanks or tabs, a
^ is inserted between the two. If an unquoted word immedi-
ately follows a $ and contains a character other than an
alphanumeric, or underscore, a ^ is inserted before the
first such character. Thus
limbo -$flags $stem.b
is equivalent to
limbo -^$flags $stem^.b
I/O Redirections
The sequence >file redirects the standard output file (file
descriptor 1, normally /dev/cons) to the named file; >>file
appends standard output to the file. The standard input file
(file descriptor 0, also normally /dev/cons) may be redi-
rected from a file by the sequence <file. The sequence
<>file opens the file for read/write and associates both
file descriptor 0 and 1 with it.
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MASH(1) MASH(1)
Compound Commands
A pair of commands separated by a pipe operator (|) is a
command. The standard output of the left command is sent
through a pipe to the standard input of the right command.
Each of the following is a command.
if ( expr ) command1
if ( expr ) command1 else command2
The expr
is evaluated and if the result is not null, then
command1 is executed. In the second form command2 is
executed if the result is null.
for ( name in list )command
The command is executed once for each word in list with
that word assigned to name.
while ( expr ) command
The expr is evaluated repeatedly until its value is
null. Each time it evaluates to non-null, the command
is executed.
case expr { pattern-list => command ... }
case expr-list { pattern => command ... }
In the first form of the command the expr is matched
against a series of lists of regular expressions (See
regex(2)). The command associated with the matching
expression is executed. In the second form the command
associated with the first pattern to match one of the
words in expr-list is executed. An expr-list will never
match a pattern-list.
{commands}
@{commands}
Braces serve to alter the grouping of commands implied
by operator priorities. The body is a sequence of com-
mands separated by & or ;. The second form is executed
with a new scope. Either form can be followed by redi-
rections.
fnname{list}
fnname
The first form defines a function with the given name.
Subsequently, whenever a command whose first word is
name is encountered, the current value of the remainder
of the command's word list will be assigned to the
local variable args, in a new scope, and mash will
execute the list. The second form removes name's func-
tion definition.
name=list
name:=list
The first form is an assignment to a variable. If the
name is currently defined as a local variable its value
will be updated. Otherwise a global variable with the
given name will be defined or updated. The second form
is an explicit definition or update of a local vari-
able.
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MASH(1) MASH(1)
list:list
list:list{commands}
word:~word{commands}
These forms define dependencies and rules for the make
loadable builtin. The first form defines a simple
dependency, the second a dependency with an explicit
rule. The third form defines an implicit rule where the
left-hand word is a file pattern, the right-hand word
is the prerequisite. The right-hand word and the com-
mands can contain references to the characters matched
by the * meta-character in the pattern ($1 evaluates to
the characters matched by the first *, $2 the second
and so on; $0 is the entire match).
Expressions
Expressions evaluate to possibly null lists of strings. A
word is an expression. An expression may take one of the
following forms
( expr )
Parentheses are used for grouping.
hd expr
tl expr
len expr
! expr
hd is the first element of a list, tl the remainder.
len is the length of a list. Both evaluate to the null
list if their operand is a null list. ! is the not
operator and evaluates to true for a null list or to a
null list otherwise.
expr ^ expr
expr :: expr
expr == expr
expr != expr
expr ~ expr
^ is concatenation (as defined above), :: is list con-
catenation, == and != are the equality operators evalu-
ating to true or the null list, depending on the equal-
ity or inequality of the two operands. ~ is the match
operator, true if a singleton string matches one of a
list of regular expressions, or one of a list of
strings matches a regular expression. (If neither
operand is a singleton it evaluates to the null list.)
^ has the highest precedence, followed by :: followed
by the other three. All associate to the left except
::.
Built-in Commands
Mash supports loadable modules of builtins. The Mashbuiltin
module definition and description is in mash.m. One such
module, builtins, is loaded before mash begins parsing. This
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MASH(1) MASH(1)
module defines the following commands
env
Print global and local variables. Global variables are
displayed using a name=value format, and local vari-
ables using a name:=value format.
eval
Concatenate arguments and use as mash input.
exit
Cause mash to raise an exit exception.
load file
Load a builtin module. The file must be a module with
type Mashbuiltin. The argument file is assumed to con-
tain a path to the loadable module. If no such module
is found then the string /dis/lib/mash/ is prepended to
file and the load is retried.
prompt
prompttext
prompttext contin
When called with no arguments causes the current value
of the mash prompt to be printed to standard output.
The default value is mash%. The second form sets a new
prompt. The final form sets a new prompt and addition-
ally a continuation string. Initially the continuation
string is set to a single tab character. Mash uses the
continuation string in place of the prompt string to
indicate that the preceding line has been continued by
escaping with a final backslash (\) character.
quoteargs...
Print arguments quoted as input for mash.
run -[denx] file [arg...]
Interpret a file as input to mash.
timecmd [arg...]
Time the execution of a command. The total execution
time is reported in seconds and on standard error when
the command completes.
whatisname
Print variable, function or builtin. The object given
by name is described on standard output in a format
that reflects its type.
The make loadable builtin provides `make` functionality.
The tk loadable builtin provides control over some of the
visual elements of a mash window.
Adding Builtins
New builtins can be added to mash by creating a Dis module
that can be loaded with a Mashbuiltin module interface
(defined in mash.m). The new module is loaded with the
builtin load command which calls its mashinit function to
initialise it with an argument containing the load command
line. The function should use this call to register the set
of builtins that the module will provide using the
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Env.defbuiltin function. Thereafter, each time one of the
registered builtins is invoked the module's mashcmd function
is called passing as an argument a list containing the
invoked builtin name and its arguments. See the examples in
mash/builtins.b, mash/make.b, and mash/tk.b.
FILES
/lib/mashinit
/dis/lib/mash
SOURCE
/appl/cmd/mash
SEE ALSO
mash-tk(1), mash-make(1), regex(2)
Tom Duff, ``Rc - The Plan 9 Shell'', in the Plan 9
Programmer's Manual , Second Edition, Volume 2.
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