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mash - programmable shell


mash [ -denx ][ -ccommand ] [ file [ arg ... ]]


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.

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.
Dump parsed commands before execution.
Fail if a top level command does.
Parse but do not execute.
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 quotation 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 executed 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 in the current directory and then in /dis. The .dis extension 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 character * 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 separated by -, standing for all characters lexically between the two. The character / must appear explicitly in a pattern. 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 prefixing /tmp.

A quoted word is a sequence of characters surrounded by single quotes ('). A single quote is escaped with a backslash.

Each of the following is a word.

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.
See the description of rules for the mash-make(1) builtin.
$".I identifier
The value is a single string containing the components of the named variable separated by spaces.
mash executes the commands and reads the standard output, splitting it into a list of words, using the whitespace characters (space, tab, newline and carriage return) as separators.
mash executes the commands and reads the standard output, splitting it into a list of words, using the whitespace characters (space, tab, newline and carriage return) as separators.

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 construction of non-linear pipelines. For example, the following runs two commands old and new and uses cmp to compare their outputs
	cmp <{old} <{new}; 
mash evaluates expr as an expression. The value is a (possibly null) list of words. Expressions are described in detail below.
The ^ operator concatenates its two operands. If either operand is a singleton, the concatenation is distributive. Otherwise the lists are concatenated pairwise.

Free Carets
In most circumstances, mash will insert the ^ operator automatically 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 immediately 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 redirected 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.

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.

Braces serve to alter the grouping of commands implied by operator priorities. The body is a sequence of commands separated by & or ;. The second form is executed with a new scope. Either form can be followed by redirections.

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 function definition.

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 variable.


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 commands 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 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 concatenation, == and != are the equality operators evaluating to true or the null list, depending on the equality 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 module defines the following commands

Print global and local variables. Global variables are displayed using a name=value format, and local variables using a name:=value format.
Concatenate arguments and use as mash input.
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 contain 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.


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 additionally 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.
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.
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 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.






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.

MASH(1 ) Rev:  Thu Feb 15 14:42:47 GMT 2007