DASH(1) BSD General Commands Manual DASH(1)
NAME
 dash -- command interpreter (shell)
SYNOPSIS
 dash [-aCefnuvxIimqVEbp] [+aCefnuvxIimqVEbp] [-o option_name]
 [+o option_name] [command_file [argument ...]]
 dash -c [-aCefnuvxIimqVEbp] [+aCefnuvxIimqVEbp] [-o option_name]
 [+o option_name] command_string [command_name [argument ...]]
 dash -s [-aCefnuvxIimqVEbp] [+aCefnuvxIimqVEbp] [-o option_name]
 [+o option_name] [argument ...]
DESCRIPTION
 dash is the standard command interpreter for the system. The current
 version of dash is in the process of being changed to conform with the
 POSIX 1003.2 and 1003.2a specifications for the shell. This version has
 many features which make it appear similar in some respects to the Korn
 shell, but it is not a Korn shell clone (see ksh(1)). Only features des-
 ignated by POSIX, plus a few Berkeley extensions, are being incorporated
 into this shell. This man page is not intended to be a tutorial or a
 complete specification of the shell.
 Overview
 The shell is a command that reads lines from either a file or the termi-
 nal, interprets them, and generally executes other commands. It is the
 program that is running when a user logs into the system (although a user
 can select a different shell with the chsh(1) command). The shell imple-
 ments a language that has flow control constructs, a macro facility that
 provides a variety of features in addition to data storage, along with
 built in history and line editing capabilities. It incorporates many
 features to aid interactive use and has the advantage that the interpre-
 tative language is common to both interactive and non-interactive use
 (shell scripts). That is, commands can be typed directly to the running
 shell or can be put into a file and the file can be executed directly by
 the shell.
 Invocation
 If no args are present and if the standard input of the shell is con-
 nected to a terminal (or if the -i flag is set), and the -c option is not
 present, the shell is considered an interactive shell. An interactive
 shell generally prompts before each command and handles programming and
 command errors differently (as described below). When first starting,
 the shell inspects argument 0, and if it begins with a dash '-', the
 shell is also considered a login shell. This is normally done automati-
 cally by the system when the user first logs in. A login shell first
 reads commands from the files /etc/profile and .profile if they exist.
 If the environment variable ENV is set on entry to an interactive shell,
 or is set in the .profile of a login shell, the shell next reads commands
 from the file named in ENV. Therefore, a user should place commands that
 are to be executed only at login time in the .profile file, and commands
 that are executed for every interactive shell inside the ENV file. To
 set the ENV variable to some file, place the following line in your
 .profile of your home directory
 ENV=$HOME/.shinit; export ENV
 substituting for ".shinit" any filename you wish.
 If command line arguments besides the options have been specified, then
 the shell treats the first argument as the name of a file from which to
 read commands (a shell script), and the remaining arguments are set as
 the positional parameters of the shell (1,ドル 2,ドル etc). Otherwise, the
 shell reads commands from its standard input.
 Argument List Processing
 All of the single letter options that have a corresponding name can be
 used as an argument to the -o option. The set -o name is provided next
 to the single letter option in the description below. Specifying a dash
 "-" turns the option on, while using a plus "+" disables the option. The
 following options can be set from the command line or with the set
 builtin (described later).
 -a allexport Export all variables assigned to.
 -c Read commands from the command_string operand in-
 stead of from the standard input. Special parame-
 ter 0 will be set from the command_name operand
 and the positional parameters (1,ドル 2,ドル etc.) set
 from the remaining argument operands.
 -C noclobber Don't overwrite existing files with ">".
 -e errexit If not interactive, exit immediately if any
 untested command fails. The exit status of a com-
 mand is considered to be explicitly tested if the
 command is used to control an if, elif, while, or
 until; or if the command is the left hand operand
 of an "&&" or "||" operator.
 -f noglob Disable pathname expansion.
 -n noexec If not interactive, read commands but do not exe-
 cute them. This is useful for checking the syntax
 of shell scripts.
 -u nounset Write a message to standard error when attempting
 to expand a variable that is not set, and if the
 shell is not interactive, exit immediately.
 -v verbose The shell writes its input to standard error as it
 is read. Useful for debugging.
 -x xtrace Write each command to standard error (preceded by
 a '+ ') before it is executed. Useful for debug-
 ging.
 -I ignoreeof Ignore EOF's from input when interactive.
 -i interactive Force the shell to behave interactively.
 -l Make dash act as if it had been invoked as a login
 shell.
 -m monitor Turn on job control (set automatically when inter-
 active).
 -s stdin Read commands from standard input (set automati-
 cally if no file arguments are present). This op-
 tion has no effect when set after the shell has
 already started running (i.e. with set).
 -V vi Enable the built-in vi(1) command line editor
 (disables -E if it has been set).
 -E emacs Enable the built-in emacs(1) command line editor
 (disables -V if it has been set).
 -b notify Enable asynchronous notification of background job
 completion. (UNIMPLEMENTED for 4.4alpha)
 -p priviliged Do not attempt to reset effective uid if it does
 not match uid. This is not set by default to help
 avoid incorrect usage by setuid root programs via
 system(3) or popen(3).
 Lexical Structure
 The shell reads input in terms of lines from a file and breaks it up into
 words at whitespace (blanks and tabs), and at certain sequences of char-
 acters that are special to the shell called "operators". There are two
 types of operators: control operators and redirection operators (their
 meaning is discussed later). Following is a list of operators:
 Control operators:
 & && ( ) ; ;; | || <newline>
 Redirection operators:
 < >>| << >> <& >& <<- <>
 Quoting
 Quoting is used to remove the special meaning of certain characters or
 words to the shell, such as operators, whitespace, or keywords. There
 are three types of quoting: matched single quotes, matched double quotes,
 and backslash.
 Backslash
 A backslash preserves the literal meaning of the following character,
 with the exception of <newline>. A backslash preceding a <newline> is
 treated as a line continuation.
 Single Quotes
 Enclosing characters in single quotes preserves the literal meaning of
 all the characters (except single quotes, making it impossible to put
 single-quotes in a single-quoted string).
 Double Quotes
 Enclosing characters within double quotes preserves the literal meaning
 of all characters except dollarsign ($), backquote (`), and backslash
 (\). The backslash inside double quotes is historically weird, and
 serves to quote only the following characters:
 $ ` " \ <newline>.
 Otherwise it remains literal.
 Reserved Words
 Reserved words are words that have special meaning to the shell and are
 recognized at the beginning of a line and after a control operator. The
 following are reserved words:
 ! elif fi while case
 else for then { }
 do done until if esac
 Their meaning is discussed later.
 Aliases
 An alias is a name and corresponding value set using the alias(1) builtin
 command. Whenever a reserved word may occur (see above), and after
 checking for reserved words, the shell checks the word to see if it
 matches an alias. If it does, it replaces it in the input stream with
 its value. For example, if there is an alias called "lf" with the value
 "ls -F", then the input:
 lf foobar <return>
 would become
 ls -F foobar <return>
 Aliases provide a convenient way for naive users to create shorthands for
 commands without having to learn how to create functions with arguments.
 They can also be used to create lexically obscure code. This use is dis-
 couraged.
 Commands
 The shell interprets the words it reads according to a language, the
 specification of which is outside the scope of this man page (refer to
 the BNF in the POSIX 1003.2 document). Essentially though, a line is
 read and if the first word of the line (or after a control operator) is
 not a reserved word, then the shell has recognized a simple command.
 Otherwise, a complex command or some other special construct may have
 been recognized.
 Simple Commands
 If a simple command has been recognized, the shell performs the following
 actions:
 1. Leading words of the form "name=value" are stripped off and
 assigned to the environment of the simple command. Redirect-
 ion operators and their arguments (as described below) are
 stripped off and saved for processing.
 2. The remaining words are expanded as described in the section
 called "Expansions", and the first remaining word is consid-
 ered the command name and the command is located. The remain-
 ing words are considered the arguments of the command. If no
 command name resulted, then the "name=value" variable assign-
 ments recognized in item 1 affect the current shell.
 3. Redirections are performed as described in the next section.
 Redirections
 Redirections are used to change where a command reads its input or sends
 its output. In general, redirections open, close, or duplicate an exist-
 ing reference to a file. The overall format used for redirection is:
 [n] redir-op file
 where redir-op is one of the redirection operators mentioned previously.
 Following is a list of the possible redirections. The [n] is an optional
 number between 0 and 9, as in '3' (not '[3]'), that refers to a file de-
 scriptor.
 [n]> file Redirect standard output (or n) to file.
 [n]>| file Same, but override the -C option.
 [n]>> file Append standard output (or n) to file.
 [n]< file Redirect standard input (or n) from file.
 [n1]<&n2 Copy file descriptor n2 as stdout (or fd n1). fd n2.
 [n]<&- Close standard input (or n).
 [n1]>&n2 Copy file descriptor n2 as stdin (or fd n1). fd n2.
 [n]>&- Close standard output (or n).
 [n]<> file Open file for reading and writing on standard input (or
 n).
 The following redirection is often called a "here-document".
 [n]<< delimiter
 here-doc-text ...
 delimiter
 All the text on successive lines up to the delimiter is saved away and
 made available to the command on standard input, or file descriptor n if
 it is specified. If the delimiter as specified on the initial line is
 quoted, then the here-doc-text is treated literally, otherwise the text
 is subjected to parameter expansion, command substitution, and arithmetic
 expansion (as described in the section on "Expansions"). If the operator
 is "<<-" instead of "<<", then leading tabs in the here-doc-text are
 stripped.
 Search and Execution
 There are three types of commands: shell functions, builtin commands, and
 normal programs - and the command is searched for (by name) in that or-
 der. They each are executed in a different way.
 When a shell function is executed, all of the shell positional parameters
 (except 0,ドル which remains unchanged) are set to the arguments of the
 shell function. The variables which are explicitly placed in the envi-
 ronment of the command (by placing assignments to them before the func-
 tion name) are made local to the function and are set to the values
 given. Then the command given in the function definition is executed.
 The positional parameters are restored to their original values when the
 command completes. This all occurs within the current shell.
 Shell builtins are executed internally to the shell, without spawning a
 new process.
 Otherwise, if the command name doesn't match a function or builtin, the
 command is searched for as a normal program in the file system (as de-
 scribed in the next section). When a normal program is executed, the
 shell runs the program, passing the arguments and the environment to the
 program. If the program is not a normal executable file (i.e., if it
 does not begin with the "magic number" whose ASCII representation is
 "#!", so execve(2) returns ENOEXEC then) the shell will interpret the
 program in a subshell. The child shell will reinitialize itself in this
 case, so that the effect will be as if a new shell had been invoked to
 handle the ad-hoc shell script, except that the location of hashed com-
 mands located in the parent shell will be remembered by the child.
 Note that previous versions of this document and the source code itself
 misleadingly and sporadically refer to a shell script without a magic
 number as a "shell procedure".
 Path Search
 When locating a command, the shell first looks to see if it has a shell
 function by that name. Then it looks for a builtin command by that name.
 If a builtin command is not found, one of two things happen:
 1. Command names containing a slash are simply executed without per-
 forming any searches.
 2. The shell searches each entry in PATH in turn for the command. The
 value of the PATH variable should be a series of entries separated
 by colons. Each entry consists of a directory name. The current
 directory may be indicated implicitly by an empty directory name, or
 explicitly by a single period.
 Command Exit Status
 Each command has an exit status that can influence the behaviour of other
 shell commands. The paradigm is that a command exits with zero for nor-
 mal or success, and non-zero for failure, error, or a false indication.
 The man page for each command should indicate the various exit codes and
 what they mean. Additionally, the builtin commands return exit codes, as
 does an executed shell function.
 If a command consists entirely of variable assignments then the exit sta-
 tus of the command is that of the last command substitution if any, oth-
 erwise 0.
 Complex Commands
 Complex commands are combinations of simple commands with control opera-
 tors or reserved words, together creating a larger complex command. More
 generally, a command is one of the following:
 o simple command
 o pipeline
 o list or compound-list
 o compound command
 o function definition
 Unless otherwise stated, the exit status of a command is that of the last
 simple command executed by the command.
 Pipelines
 A pipeline is a sequence of one or more commands separated by the control
 operator |. The standard output of all but the last command is connected
 to the standard input of the next command. The standard output of the
 last command is inherited from the shell, as usual.
 The format for a pipeline is:
 [!] command1 [| command2 ...]
 The standard output of command1 is connected to the standard input of
 command2. The standard input, standard output, or both of a command is
 considered to be assigned by the pipeline before any redirection speci-
 fied by redirection operators that are part of the command.
 If the pipeline is not in the background (discussed later), the shell
 waits for all commands to complete.
 If the reserved word ! does not precede the pipeline, the exit status is
 the exit status of the last command specified in the pipeline. Other-
 wise, the exit status is the logical NOT of the exit status of the last
 command. That is, if the last command returns zero, the exit status is
 1; if the last command returns greater than zero, the exit status is
 zero.
 Because pipeline assignment of standard input or standard output or both
 takes place before redirection, it can be modified by redirection. For
 example:
 $ command1 2>&1 | command2
 sends both the standard output and standard error of command1 to the
 standard input of command2.
 A ; or <newline> terminator causes the preceding AND-OR-list (described
 next) to be executed sequentially; a & causes asynchronous execution of
 the preceding AND-OR-list.
 Note that unlike some other shells, each process in the pipeline is a
 child of the invoking shell (unless it is a shell builtin, in which case
 it executes in the current shell - but any effect it has on the environ-
 ment is wiped).
 Background Commands - &
 If a command is terminated by the control operator ampersand (&), the
 shell executes the command asynchronously - that is, the shell does not
 wait for the command to finish before executing the next command.
 The format for running a command in background is:
 command1 & [command2 & ...]
 If the shell is not interactive, the standard input of an asynchronous
 command is set to /dev/null.
 Lists - Generally Speaking
 A list is a sequence of zero or more commands separated by newlines,
 semicolons, or ampersands, and optionally terminated by one of these
 three characters. The commands in a list are executed in the order they
 are written. If command is followed by an ampersand, the shell starts
 the command and immediately proceeds onto the next command; otherwise it
 waits for the command to terminate before proceeding to the next one.
 Short-Circuit List Operators
 "&&" and "||" are AND-OR list operators. "&&" executes the first com-
 mand, and then executes the second command if and only if the exit status
 of the first command is zero. "||" is similar, but executes the second
 command if and only if the exit status of the first command is nonzero.
 "&&" and "||" both have the same priority.
 Flow-Control Constructs - if, while, for, case
 The syntax of the if command is
 if list
 then list
 [ elif list
 then list ] ...
 [ else list ]
 fi
 The syntax of the while command is
 while list
 do list
 done
 The two lists are executed repeatedly while the exit status of the first
 list is zero. The until command is similar, but has the word until in
 place of while, which causes it to repeat until the exit status of the
 first list is zero.
 The syntax of the for command is
 for variable [ in [ word ... ] ]
 do list
 done
 The words following in are expanded, and then the list is executed re-
 peatedly with the variable set to each word in turn. Omitting in word
 ... is equivalent to in "$@".
 The syntax of the break and continue command is
 break [ num ]
 continue [ num ]
 Break terminates the num innermost for or while loops. Continue contin-
 ues with the next iteration of the innermost loop. These are implemented
 as builtin commands.
 The syntax of the case command is
 case word in
 [(]pattern) list ;;
 ...
 esac
 The pattern can actually be one or more patterns (see Shell Patterns de-
 scribed later), separated by "|" characters. The "(" character before
 the pattern is optional.
 Grouping Commands Together
 Commands may be grouped by writing either
 (list)
 or
 { list; }
 The first of these executes the commands in a subshell. Builtin commands
 grouped into a (list) will not affect the current shell. The second form
 does not fork another shell so is slightly more efficient. Grouping com-
 mands together this way allows you to redirect their output as though
 they were one program:
 { printf " hello " ; printf " world\n" ; } > greeting
 Note that "}" must follow a control operator (here, ";") so that it is
 recognized as a reserved word and not as another command argument.
 Functions
 The syntax of a function definition is
 name () command
 A function definition is an executable statement; when executed it in-
 stalls a function named name and returns an exit status of zero. The
 command is normally a list enclosed between "{" and "}".
 Variables may be declared to be local to a function by using a local com-
 mand. This should appear as the first statement of a function, and the
 syntax is
 local [variable | -] ...
 Local is implemented as a builtin command.
 When a variable is made local, it inherits the initial value and exported
 and readonly flags from the variable with the same name in the surround-
 ing scope, if there is one. Otherwise, the variable is initially unset.
 The shell uses dynamic scoping, so that if you make the variable x local
 to function f, which then calls function g, references to the variable x
 made inside g will refer to the variable x declared inside f, not to the
 global variable named x.
 The only special parameter that can be made local is "-". Making "-" lo-
 cal any shell options that are changed via the set command inside the
 function to be restored to their original values when the function re-
 turns.
 The syntax of the return command is
 return [exitstatus]
 It terminates the currently executing function. Return is implemented as
 a builtin command.
 Variables and Parameters
 The shell maintains a set of parameters. A parameter denoted by a name
 is called a variable. When starting up, the shell turns all the environ-
 ment variables into shell variables. New variables can be set using the
 form
 name=value
 Variables set by the user must have a name consisting solely of alphabet-
 ics, numerics, and underscores - the first of which must not be numeric.
 A parameter can also be denoted by a number or a special character as ex-
 plained below.
 Positional Parameters
 A positional parameter is a parameter denoted by a number (n > 0). The
 shell sets these initially to the values of its command line arguments
 that follow the name of the shell script. The set builtin can also be
 used to set or reset them.
 Special Parameters
 A special parameter is a parameter denoted by one of the following spe-
 cial characters. The value of the parameter is listed next to its char-
 acter.
 * Expands to the positional parameters, starting from one.
 When the expansion occurs within a double-quoted string it
 expands to a single field with the value of each parameter
 separated by the first character of the IFS variable, or by
 a <space> if IFS is unset.
 @ Expands to the positional parameters, starting from one.
 When the expansion occurs within double-quotes, each posi-
 tional parameter expands as a separate argument. If there
 are no positional parameters, the expansion of @ generates
 zero arguments, even when @ is double-quoted. What this ba-
 sically means, for example, is if 1ドル is "abc" and 2ドル is "def
 ghi", then "$@" expands to the two arguments:
 "abc" "def ghi"
 # Expands to the number of positional parameters.
 ? Expands to the exit status of the most recent pipeline.
 - (Hyphen.) Expands to the current option flags (the single-letter op-
 tion names concatenated into a string) as specified on invo-
 cation, by the set builtin command, or implicitly by the
 shell.
 $ Expands to the process ID of the invoked shell. A subshell
 retains the same value of $ as its parent.
 ! Expands to the process ID of the most recent background com-
 mand executed from the current shell. For a pipeline, the
 process ID is that of the last command in the pipeline.
 0 (Zero.) Expands to the name of the shell or shell script.
 Word Expansions
 This clause describes the various expansions that are performed on words.
 Not all expansions are performed on every word, as explained later.
 Tilde expansions, parameter expansions, command substitutions, arithmetic
 expansions, and quote removals that occur within a single word expand to
 a single field. It is only field splitting or pathname expansion that
 can create multiple fields from a single word. The single exception to
 this rule is the expansion of the special parameter @ within double-
 quotes, as was described above.
 The order of word expansion is:
 1. Tilde Expansion, Parameter Expansion, Command Substitution, Arith-
 metic Expansion (these all occur at the same time).
 2. Field Splitting is performed on fields generated by step (1) unless
 the IFS variable is null.
 3. Pathname Expansion (unless set -f is in effect).
 4. Quote Removal.
 The $ character is used to introduce parameter expansion, command substi-
 tution, or arithmetic evaluation.
 Tilde Expansion (substituting a user's home directory)
 A word beginning with an unquoted tilde character (~) is subjected to
 tilde expansion. All the characters up to a slash (/) or the end of the
 word are treated as a username and are replaced with the user's home di-
 rectory. If the username is missing (as in ~/foobar), the tilde is re-
 placed with the value of the HOME variable (the current user's home di-
 rectory).
 Parameter Expansion
 The format for parameter expansion is as follows:
 ${expression}
 where expression consists of all characters until the matching "}". Any
 "}" escaped by a backslash or within a quoted string, and characters in
 embedded arithmetic expansions, command substitutions, and variable ex-
 pansions, are not examined in determining the matching "}".
 The simplest form for parameter expansion is:
 ${parameter}
 The value, if any, of parameter is substituted.
 The parameter name or symbol can be enclosed in braces, which are op-
 tional except for positional parameters with more than one digit or when
 parameter is followed by a character that could be interpreted as part of
 the name. If a parameter expansion occurs inside double-quotes:
 1. Pathname expansion is not performed on the results of the expansion.
 2. Field splitting is not performed on the results of the expansion,
 with the exception of @.
 In addition, a parameter expansion can be modified by using one of the
 following formats.
 ${parameter:-word} Use Default Values. If parameter is unset or null,
 the expansion of word is substituted; otherwise,
 the value of parameter is substituted.
 ${parameter:=word} Assign Default Values. If parameter is unset or
 null, the expansion of word is assigned to parame-
 ter. In all cases, the final value of parameter is
 substituted. Only variables, not positional param-
 eters or special parameters, can be assigned in
 this way.
 ${parameter:?[word]} Indicate Error if Null or Unset. If parameter is
 unset or null, the expansion of word (or a message
 indicating it is unset if word is omitted) is writ-
 ten to standard error and the shell exits with a
 nonzero exit status. Otherwise, the value of pa-
 rameter is substituted. An interactive shell need
 not exit.
 ${parameter:+word} Use Alternative Value. If parameter is unset or
 null, null is substituted; otherwise, the expansion
 of word is substituted.
 In the parameter expansions shown previously, use of the colon in the
 format results in a test for a parameter that is unset or null; omission
 of the colon results in a test for a parameter that is only unset.
 ${#parameter} String Length. The length in characters of the
 value of parameter.
 The following four varieties of parameter expansion provide for substring
 processing. In each case, pattern matching notation (see Shell
 Patterns), rather than regular expression notation, is used to evaluate
 the patterns. If parameter is * or @, the result of the expansion is un-
 specified. Enclosing the full parameter expansion string in double-
 quotes does not cause the following four varieties of pattern characters
 to be quoted, whereas quoting characters within the braces has this ef-
 fect.
 ${parameter%word} Remove Smallest Suffix Pattern. The word is ex-
 panded to produce a pattern. The parameter expan-
 sion then results in parameter, with the smallest
 portion of the suffix matched by the pattern
 deleted.
 ${parameter%%word} Remove Largest Suffix Pattern. The word is ex-
 panded to produce a pattern. The parameter expan-
 sion then results in parameter, with the largest
 portion of the suffix matched by the pattern
 deleted.
 ${parameter#word} Remove Smallest Prefix Pattern. The word is ex-
 panded to produce a pattern. The parameter expan-
 sion then results in parameter, with the smallest
 portion of the prefix matched by the pattern
 deleted.
 ${parameter##word} Remove Largest Prefix Pattern. The word is ex-
 panded to produce a pattern. The parameter expan-
 sion then results in parameter, with the largest
 portion of the prefix matched by the pattern
 deleted.
 Command Substitution
 Command substitution allows the output of a command to be substituted in
 place of the command name itself. Command substitution occurs when the
 command is enclosed as follows:
 $(command)
 or ("backquoted" version):
 `command`
 The shell expands the command substitution by executing command in a sub-
 shell environment and replacing the command substitution with the stan-
 dard output of the command, removing sequences of one or more <newline>s
 at the end of the substitution. (Embedded <newline>s before the end of
 the output are not removed; however, during field splitting, they may be
 translated into <space>s, depending on the value of IFS and quoting that
 is in effect.)
 Arithmetic Expansion
 Arithmetic expansion provides a mechanism for evaluating an arithmetic
 expression and substituting its value. The format for arithmetic expan-
 sion is as follows:
 $((expression))
 The expression is treated as if it were in double-quotes, except that a
 double-quote inside the expression is not treated specially. The shell
 expands all tokens in the expression for parameter expansion, command
 substitution, and quote removal.
 Next, the shell treats this as an arithmetic expression and substitutes
 the value of the expression.
 White Space Splitting (Field Splitting)
 After parameter expansion, command substitution, and arithmetic expansion
 the shell scans the results of expansions and substitutions that did not
 occur in double-quotes for field splitting and multiple fields can re-
 sult.
 The shell treats each character of the IFS as a delimiter and uses the
 delimiters to split the results of parameter expansion and command sub-
 stitution into fields.
 Pathname Expansion (File Name Generation)
 Unless the -f flag is set, file name generation is performed after word
 splitting is complete. Each word is viewed as a series of patterns, sep-
 arated by slashes. The process of expansion replaces the word with the
 names of all existing files whose names can be formed by replacing each
 pattern with a string that matches the specified pattern. There are two
 restrictions on this: first, a pattern cannot match a string containing a
 slash, and second, a pattern cannot match a string starting with a period
 unless the first character of the pattern is a period. The next section
 describes the patterns used for both Pathname Expansion and the case com-
 mand.
 Shell Patterns
 A pattern consists of normal characters, which match themselves, and
 meta-characters. The meta-characters are "!", "*", "?", and "[". These
 characters lose their special meanings if they are quoted. When command
 or variable substitution is performed and the dollar sign or back quotes
 are not double quoted, the value of the variable or the output of the
 command is scanned for these characters and they are turned into meta-
 characters.
 An asterisk ("*") matches any string of characters. A question mark
 matches any single character. A left bracket ("[") introduces a charac-
 ter class. The end of the character class is indicated by a ("]"); if
 the "]" is missing then the "[" matches a "[" rather than introducing a
 character class. A character class matches any of the characters between
 the square brackets. A range of characters may be specified using a mi-
 nus sign. The character class may be complemented by making an exclama-
 tion point the first character of the character class.
 To include a "]" in a character class, make it the first character listed
 (after the "!", if any). To include a minus sign, make it the first or
 last character listed.
 Builtins
 This section lists the builtin commands which are builtin because they
 need to perform some operation that can't be performed by a separate
 process. In addition to these, there are several other commands that may
 be builtin for efficiency (e.g. printf(1), echo(1), test(1), etc).
 :
 true A null command that returns a 0 (true) exit value.
 . file
 The commands in the specified file are read and executed by the
 shell.
 alias [name[=string ...]]
 If name=string is specified, the shell defines the alias name with
 value string. If just name is specified, the value of the alias
 name is printed. With no arguments, the alias builtin prints the
 names and values of all defined aliases (see unalias).
 bg [job] ...
 Continue the specified jobs (or the current job if no jobs are
 given) in the background.
 command [-p] [-v] [-V] command [arg ...]
 Execute the specified command but ignore shell functions when
 searching for it. (This is useful when you have a shell function
 with the same name as a builtin command.)
 -p search for command using a PATH that guarantees to find all
 the standard utilities.
 -V Do not execute the command but search for the command and
 print the resolution of the command search. This is the
 same as the type builtin.
 -v Do not execute the command but search for the command and
 print the absolute pathname of utilities, the name for
 builtins or the expansion of aliases.
 cd -
 cd [-LP] [directory]
 Switch to the specified directory (default HOME). If an entry for
 CDPATH appears in the environment of the cd command or the shell
 variable CDPATH is set and the directory name does not begin with
 a slash, then the directories listed in CDPATH will be searched
 for the specified directory. The format of CDPATH is the same as
 that of PATH. If a single dash is specified as the argument, it
 will be replaced by the value of OLDPWD. The cd command will
 print out the name of the directory that it actually switched to
 if this is different from the name that the user gave. These may
 be different either because the CDPATH mechanism was used or be-
 cause the argument is a single dash. The -P option causes the
 physical directory structure to be used, that is, all symbolic
 links are resolved to their respective values. The -L option
 turns off the effect of any preceding -P options.
 echo [-n] args...
 Print the arguments on the standard output, separated by spaces.
 Unless the -n option is present, a newline is output following the
 arguments.
 If any of the following sequences of characters is encountered
 during output, the sequence is not output. Instead, the specified
 action is performed:
 \b A backspace character is output.
 \c Subsequent output is suppressed. This is normally used at
 the end of the last argument to suppress the trailing new-
 line that echo would otherwise output.
 \e Outputs an escape character (ESC).
 \f Output a form feed.
 \n Output a newline character.
 \r Output a carriage return.
 \t Output a (horizontal) tab character.
 \v Output a vertical tab.
 0円digits
 Output the character whose value is given by zero to three
 octal digits. If there are zero digits, a nul character
 is output.
 \\ Output a backslash.
 All other backslash sequences elicit undefined behaviour.
 eval string ...
 Concatenate all the arguments with spaces. Then re-parse and exe-
 cute the command.
 exec [command arg ...]
 Unless command is omitted, the shell process is replaced with the
 specified program (which must be a real program, not a shell
 builtin or function). Any redirections on the exec command are
 marked as permanent, so that they are not undone when the exec
 command finishes.
 exit [exitstatus]
 Terminate the shell process. If exitstatus is given it is used as
 the exit status of the shell; otherwise the exit status of the
 preceding command is used.
 export name ...
 export -p
 The specified names are exported so that they will appear in the
 environment of subsequent commands. The only way to un-export a
 variable is to unset it. The shell allows the value of a variable
 to be set at the same time it is exported by writing
 export name=value
 With no arguments the export command lists the names of all ex-
 ported variables. With the -p option specified the output will be
 formatted suitably for non-interactive use.
 fc [-e editor] [first [last]]
 fc -l [-nr] [first [last]]
 fc -s [old=new] [first]
 The fc builtin lists, or edits and re-executes, commands previ-
 ously entered to an interactive shell.
 -e editor
 Use the editor named by editor to edit the commands. The
 editor string is a command name, subject to search via the
 PATH variable. The value in the FCEDIT variable is used as
 a default when -e is not specified. If FCEDIT is null or
 unset, the value of the EDITOR variable is used. If EDITOR
 is null or unset, ed(1) is used as the editor.
 -l (ell)
 List the commands rather than invoking an editor on them.
 The commands are written in the sequence indicated by the
 first and last operands, as affected by -r, with each com-
 mand preceded by the command number.
 -n Suppress command numbers when listing with -l.
 -r Reverse the order of the commands listed (with -l) or
 edited (with neither -l nor -s).
 -s Re-execute the command without invoking an editor.
 first
 last Select the commands to list or edit. The number of previ-
 ous commands that can be accessed are determined by the
 value of the HISTSIZE variable. The value of first or last
 or both are one of the following:
 [+]number
 A positive number representing a command number;
 command numbers can be displayed with the -l option.
 -number
 A negative decimal number representing the command
 that was executed number of commands previously.
 For example, -1 is the immediately previous command.
 string
 A string indicating the most recently entered command that
 begins with that string. If the old=new operand is not
 also specified with -s, the string form of the first oper-
 and cannot contain an embedded equal sign.
 The following environment variables affect the execution of fc:
 FCEDIT Name of the editor to use.
 HISTSIZE The number of previous commands that are accessible.
 fg [job]
 Move the specified job or the current job to the foreground.
 getopts optstring var
 The POSIX getopts command, not to be confused with the Bell Labs
 -derived getopt(1).
 The first argument should be a series of letters, each of which
 may be optionally followed by a colon to indicate that the option
 requires an argument. The variable specified is set to the parsed
 option.
 The getopts command deprecates the older getopt(1) utility due to
 its handling of arguments containing whitespace.
 The getopts builtin may be used to obtain options and their argu-
 ments from a list of parameters. When invoked, getopts places the
 value of the next option from the option string in the list in the
 shell variable specified by var and its index in the shell vari-
 able OPTIND. When the shell is invoked, OPTIND is initialized to
 1. For each option that requires an argument, the getopts builtin
 will place it in the shell variable OPTARG. If an option is not
 allowed for in the optstring, then OPTARG will be unset.
 optstring is a string of recognized option letters (see
 getopt(3)). If a letter is followed by a colon, the option is ex-
 pected to have an argument which may or may not be separated from
 it by white space. If an option character is not found where ex-
 pected, getopts will set the variable var to a "?"; getopts will
 then unset OPTARG and write output to standard error. By specify-
 ing a colon as the first character of optstring all errors will be
 ignored.
 After the last option getopts will return a non-zero value and set
 var to "?".
 The following code fragment shows how one might process the argu-
 ments for a command that can take the options [a] and [b], and the
 option [c], which requires an argument.
 while getopts abc: f
 do
 case $f in
 a | b) flag=$f;;
 c) carg=$OPTARG;;
 \?) echo $USAGE; exit 1;;
 esac
 done
 shift `expr $OPTIND - 1`
 This code will accept any of the following as equivalent:
 cmd -acarg file file
 cmd -a -c arg file file
 cmd -carg -a file file
 cmd -a -carg -- file file
 hash -rv command ...
 The shell maintains a hash table which remembers the locations of
 commands. With no arguments whatsoever, the hash command prints
 out the contents of this table. Entries which have not been
 looked at since the last cd command are marked with an asterisk;
 it is possible for these entries to be invalid.
 With arguments, the hash command removes the specified commands
 from the hash table (unless they are functions) and then locates
 them. With the -v option, hash prints the locations of the com-
 mands as it finds them. The -r option causes the hash command to
 delete all the entries in the hash table except for functions.
 pwd [-LP]
 builtin command remembers what the current directory is rather
 than recomputing it each time. This makes it faster. However, if
 the current directory is renamed, the builtin version of pwd will
 continue to print the old name for the directory. The -P option
 causes the physical value of the current working directory to be
 shown, that is, all symbolic links are resolved to their respec-
 tive values. The -L option turns off the effect of any preceding
 -P options.
 read [-p prompt] [-r] variable [...]
 The prompt is printed if the -p option is specified and the stan-
 dard input is a terminal. Then a line is read from the standard
 input. The trailing newline is deleted from the line and the line
 is split as described in the section on word splitting above, and
 the pieces are assigned to the variables in order. At least one
 variable must be specified. If there are more pieces than vari-
 ables, the remaining pieces (along with the characters in IFS that
 separated them) are assigned to the last variable. If there are
 more variables than pieces, the remaining variables are assigned
 the null string. The read builtin will indicate success unless
 EOF is encountered on input, in which case failure is returned.
 By default, unless the -r option is specified, the backslash "\"
 acts as an escape character, causing the following character to be
 treated literally. If a backslash is followed by a newline, the
 backslash and the newline will be deleted.
 readonly name ...
 readonly -p
 The specified names are marked as read only, so that they cannot
 be subsequently modified or unset. The shell allows the value of
 a variable to be set at the same time it is marked read only by
 writing
 readonly name=value
 With no arguments the readonly command lists the names of all read
 only variables. With the -p option specified the output will be
 formatted suitably for non-interactive use.
 printf format [arguments ...]
 printf formats and prints its arguments, after the first, under
 control of the format. The format is a character string which
 contains three types of objects: plain characters, which are sim-
 ply copied to standard output, character escape sequences which
 are converted and copied to the standard output, and format speci-
 fications, each of which causes printing of the next successive
 argument.
 The arguments after the first are treated as strings if the corre-
 sponding format is either b, c or s; otherwise it is evaluated as
 a C constant, with the following extensions:
 o A leading plus or minus sign is allowed.
 o If the leading character is a single or double quote,
 the value is the ASCII code of the next character.
 The format string is reused as often as necessary to satisfy the
 arguments. Any extra format specifications are evaluated with
 zero or the null string.
 Character escape sequences are in backslash notation as defined in
 ANSI X3.159-1989 ("ANSI C89"). The characters and their meanings
 are as follows:
 \a Write a <bell> character.
 \b Write a <backspace> character.
 \e Write an <escape> (ESC) character.
 \f Write a <form-feed> character.
 \n Write a <new-line> character.
 \r Write a <carriage return> character.
 \t Write a <tab> character.
 \v Write a <vertical tab> character.
 \\ Write a backslash character.
 \num Write an 8-bit character whose ASCII value is the
 1-, 2-, or 3-digit octal number num.
 Each format specification is introduced by the percent character
 (``%''). The remainder of the format specification includes, in
 the following order:
 Zero or more of the following flags:
 # A `#' character specifying that the value should
 be printed in an ``alternative form''. For b, c,
 d, and s formats, this option has no effect. For
 the o format the precision of the number is in-
 creased to force the first character of the output
 string to a zero. For the x (X) format, a non-
 zero result has the string 0x (0X) prepended to
 it. For e, E, f, g, and G formats, the result
 will always contain a decimal point, even if no
 digits follow the point (normally, a decimal point
 only appears in the results of those formats if a
 digit follows the decimal point). For g and G
 formats, trailing zeros are not removed from the
 result as they would otherwise be.
 - A minus sign `-' which specifies left adjustment
 of the output in the indicated field;
 + A `+' character specifying that there should al-
 ways be a sign placed before the number when using
 signed formats.
 ' ' A space specifying that a blank should be left be-
 fore a positive number for a signed format. A `+'
 overrides a space if both are used;
 0 A zero `0' character indicating that zero-padding
 should be used rather than blank-padding. A `-'
 overrides a `0' if both are used;
 Field Width:
 An optional digit string specifying a field width; if the
 output string has fewer characters than the field width it
 will be blank-padded on the left (or right, if the left-
 adjustment indicator has been given) to make up the field
 width (note that a leading zero is a flag, but an embedded
 zero is part of a field width);
 Precision:
 An optional period, '.', followed by an optional digit
 string giving a precision which specifies the number of
 digits to appear after the decimal point, for e and f for-
 mats, or the maximum number of bytes to be printed from a
 string (b and s formats); if the digit string is missing,
 the precision is treated as zero;
 Format:
 A character which indicates the type of format to use (one
 of diouxXfwEgGbcs).
 A field width or precision may be '*' instead of a digit string.
 In this case an argument supplies the field width or precision.
 The format characters and their meanings are:
 diouXx The argument is printed as a signed decimal (d or i),
 unsigned octal, unsigned decimal, or unsigned hexadec-
 imal (X or x), respectively.
 f The argument is printed in the style [-]ddd.ddd where
 the number of d's after the decimal point is equal to
 the precision specification for the argument. If the
 precision is missing, 6 digits are given; if the pre-
 cision is explicitly 0, no digits and no decimal point
 are printed.
 eE The argument is printed in the style [-]d.ddde+-dd
 where there is one digit before the decimal point and
 the number after is equal to the precision specifica-
 tion for the argument; when the precision is missing,
 6 digits are produced. An upper-case E is used for an
 `E' format.
 gG The argument is printed in style f or in style e (E)
 whichever gives full precision in minimum space.
 b Characters from the string argument are printed with
 backslash-escape sequences expanded.
 The following additional backslash-escape sequences
 are supported:
 \c Causes dash to ignore any remaining characters
 in the string operand containing it, any re-
 maining string operands, and any additional
 characters in the format operand.
 0円num Write an 8-bit character whose ASCII value is
 the 1-, 2-, or 3-digit octal number num.
 c The first character of argument is printed.
 s Characters from the string argument are printed until
 the end is reached or until the number of bytes indi-
 cated by the precision specification is reached; if
 the precision is omitted, all characters in the string
 are printed.
 % Print a `%'; no argument is used.
 In no case does a non-existent or small field width cause trunca-
 tion of a field; padding takes place only if the specified field
 width exceeds the actual width.
 set [{ -options | +options | -- }] arg ...
 The set command performs three different functions.
 With no arguments, it lists the values of all shell variables.
 If options are given, it sets the specified option flags, or
 clears them as described in the section called Argument List
 Processing. As a special case, if the option is -o or +o and no
 argument is supplied, the shell prints the settings of all its op-
 tions. If the option is -o, the settings are printed in a human-
 readable format; if the option is +o, the settings are printed in
 a format suitable for reinput to the shell to affect the same op-
 tion settings.
 The third use of the set command is to set the values of the
 shell's positional parameters to the specified args. To change
 the positional parameters without changing any options, use "--"
 as the first argument to set. If no args are present, the set
 command will clear all the positional parameters (equivalent to
 executing "shift $#".)
 shift [n]
 Shift the positional parameters n times. A shift sets the value
 of 1ドル to the value of 2,ドル the value of 2ドル to the value of 3,ドル and
 so on, decreasing the value of $# by one. If n is greater than
 the number of positional parameters, shift will issue an error
 message, and exit with return status 2.
 test expression
 [ expression ]
 The test utility evaluates the expression and, if it evaluates to
 true, returns a zero (true) exit status; otherwise it returns 1
 (false). If there is no expression, test also returns 1 (false).
 All operators and flags are separate arguments to the test util-
 ity.
 The following primaries are used to construct expression:
 -b file True if file exists and is a block special file.
 -c file True if file exists and is a character special file.
 -d file True if file exists and is a directory.
 -e file True if file exists (regardless of type).
 -f file True if file exists and is a regular file.
 -g file True if file exists and its set group ID flag is
 set.
 -h file True if file exists and is a symbolic link.
 -k file True if file exists and its sticky bit is set.
 -n string True if the length of string is nonzero.
 -p file True if file is a named pipe (FIFO).
 -r file True if file exists and is readable.
 -s file True if file exists and has a size greater than
 zero.
 -t file_descriptor
 True if the file whose file descriptor number is
 file_descriptor is open and is associated with a
 terminal.
 -u file True if file exists and its set user ID flag is set.
 -w file True if file exists and is writable. True indicates
 only that the write flag is on. The file is not
 writable on a read-only file system even if this
 test indicates true.
 -x file True if file exists and is executable. True indi-
 cates only that the execute flag is on. If file is
 a directory, true indicates that file can be
 searched.
 -z string True if the length of string is zero.
 -L file True if file exists and is a symbolic link. This
 operator is retained for compatibility with previous
 versions of this program. Do not rely on its exis-
 tence; use -h instead.
 -O file True if file exists and its owner matches the effec-
 tive user id of this process.
 -G file True if file exists and its group matches the effec-
 tive group id of this process.
 -S file True if file exists and is a socket.
 file1 -nt file2
 True if file1 and file2 exist and file1 is newer
 than file2.
 file1 -ot file2
 True if file1 and file2 exist and file1 is older
 than file2.
 file1 -ef file2
 True if file1 and file2 exist and refer to the same
 file.
 string True if string is not the null string.
 s1 = s2 True if the strings s1 and s2 are identical.
 s1 != s2 True if the strings s1 and s2 are not identical.
 s1 < s2 True if string s1 comes before s2 based on the ASCII
 value of their characters.
 s1 > s2 True if string s1 comes after s2 based on the ASCII
 value of their characters.
 n1 -eq n2 True if the integers n1 and n2 are algebraically
 equal.
 n1 -ne n2 True if the integers n1 and n2 are not algebraically
 equal.
 n1 -gt n2 True if the integer n1 is algebraically greater than
 the integer n2.
 n1 -ge n2 True if the integer n1 is algebraically greater than
 or equal to the integer n2.
 n1 -lt n2 True if the integer n1 is algebraically less than
 the integer n2.
 n1 -le n2 True if the integer n1 is algebraically less than or
 equal to the integer n2.
 These primaries can be combined with the following operators:
 ! expression True if expression is false.
 expression1 -a expression2
 True if both expression1 and expression2 are true.
 expression1 -o expression2
 True if either expression1 or expression2 are true.
 (expression) True if expression is true.
 The -a operator has higher precedence than the -o operator.
 times Print the accumulated user and system times for the shell and for
 processes run from the shell. The return status is 0.
 trap [action signal ...]
 Cause the shell to parse and execute action when any of the speci-
 fied signals are received. The signals are specified by signal
 number or as the name of the signal. If signal is 0 or EXIT, the
 action is executed when the shell exits. action may be empty
 (''), which causes the specified signals to be ignored. With
 action omitted or set to `-' the specified signals are set to
 their default action. When the shell forks off a subshell, it re-
 sets trapped (but not ignored) signals to the default action. The
 trap command has no effect on signals that were ignored on entry
 to the shell. trap without any arguments cause it to write a list
 of signals and their associated action to the standard output in a
 format that is suitable as an input to the shell that achieves the
 same trapping results.
 Examples:
 trap
 List trapped signals and their corresponding action
 trap '' INT QUIT tstp 30
 Ignore signals INT QUIT TSTP USR1
 trap date INT
 Print date upon receiving signal INT
 type [name ...]
 Interpret each name as a command and print the resolution of the
 command search. Possible resolutions are: shell keyword, alias,
 shell builtin, command, tracked alias and not found. For aliases
 the alias expansion is printed; for commands and tracked aliases
 the complete pathname of the command is printed.
 ulimit [-H | -S] [-a | -tfdscmlpnv [value]]
 Inquire about or set the hard or soft limits on processes or set
 new limits. The choice between hard limit (which no process is
 allowed to violate, and which may not be raised once it has been
 lowered) and soft limit (which causes processes to be signaled but
 not necessarily killed, and which may be raised) is made with
 these flags:
 -H set or inquire about hard limits
 -S set or inquire about soft limits. If neither -H nor
 -S is specified, the soft limit is displayed or both
 limits are set. If both are specified, the last one
 wins.
 The limit to be interrogated or set, then, is chosen by specifying
 any one of these flags:
 -a show all the current limits
 -t show or set the limit on CPU time (in seconds)
 -f show or set the limit on the largest file that can be
 created (in 512-byte blocks)
 -d show or set the limit on the data segment size of a
 process (in kilobytes)
 -s show or set the limit on the stack size of a process
 (in kilobytes)
 -c show or set the limit on the largest core dump size
 that can be produced (in 512-byte blocks)
 -m show or set the limit on the total physical memory
 that can be in use by a process (in kilobytes)
 -l show or set the limit on how much memory a process can
 lock with mlock(2) (in kilobytes)
 -p show or set the limit on the number of processes this
 user can have at one time
 -n show or set the limit on the number files a process
 can have open at once
 -v show or set the limit on the total virtual memory that
 can be in use by a process (in kilobytes)
 -r show or set the limit on the real-time scheduling pri-
 ority of a process
 If none of these is specified, it is the limit on file size that
 is shown or set. If value is specified, the limit is set to that
 number; otherwise the current limit is displayed.
 Limits of an arbitrary process can be displayed or set using the
 sysctl(8) utility.
 umask [mask]
 Set the value of umask (see umask(2)) to the specified octal
 value. If the argument is omitted, the umask value is printed.
 unalias [-a] [name]
 If name is specified, the shell removes that alias. If -a is
 specified, all aliases are removed.
 unset [-fv] name ...
 The specified variables and functions are unset and unexported.
 If -f or -v is specified, the corresponding function or variable
 is unset, respectively. If a given name corresponds to both a
 variable and a function, and no options are given, only the vari-
 able is unset.
 wait [job]
 Wait for the specified job to complete and return the exit status
 of the last process in the job. If the argument is omitted, wait
 for all jobs to complete and return an exit status of zero.
 Command Line Editing
 When dash is being used interactively from a terminal, the current com-
 mand and the command history (see fc in Builtins) can be edited using vi-
 mode command-line editing. This mode uses commands, described below,
 similar to a subset of those described in the vi man page. The command
 'set -o vi' enables vi-mode editing and places sh into vi insert mode.
 With vi-mode enabled, sh can be switched between insert mode and command
 mode. It is similar to vi: typing <ESC> enters vi command mode. Hitting
 <return> while in command mode will pass the line to the shell.
EXIT STATUS
 Errors that are detected by the shell, such as a syntax error, will cause
 the shell to exit with a non-zero exit status. If the shell is not an
 interactive shell, the execution of the shell file will be aborted. Oth-
 erwise the shell will return the exit status of the last command exe-
 cuted, or if the exit builtin is used with a numeric argument, it will
 return the argument.
ENVIRONMENT
 HOME Set automatically by login(1) from the user's login directory
 in the password file (passwd(4)). This environment variable
 also functions as the default argument for the cd builtin.
 PATH The default search path for executables. See the above sec-
 tion Path Search.
 CDPATH The search path used with the cd builtin.
 MAIL The name of a mail file, that will be checked for the arrival
 of new mail. Overridden by MAILPATH.
 MAILCHECK The frequency in seconds that the shell checks for the arrival
 of mail in the files specified by the MAILPATH or the MAIL
 file. If set to 0, the check will occur at each prompt.
 MAILPATH A colon ":" separated list of file names, for the shell to
 check for incoming mail. This environment setting overrides
 the MAIL setting. There is a maximum of 10 mailboxes that can
 be monitored at once.
 PS1 The primary prompt string, which defaults to "$ ", unless you
 are the superuser, in which case it defaults to "# ".
 PS2 The secondary prompt string, which defaults to "> ".
 PS4 Output before each line when execution trace (set -x) is en-
 abled, defaults to "+ ".
 IFS Input Field Separators. This is normally set to <space>,
 <tab>, and <newline>. See the White Space Splitting section
 for more details.
 TERM The default terminal setting for the shell. This is inherited
 by children of the shell, and is used in the history editing
 modes.
 HISTSIZE The number of lines in the history buffer for the shell.
 PWD The logical value of the current working directory. This is
 set by the cd command.
 OLDPWD The previous logical value of the current working directory.
 This is set by the cd command.
 PPID The process ID of the parent process of the shell.
FILES
 $HOME/.profile
 /etc/profile
SEE ALSO
 csh(1), echo(1), getopt(1), ksh(1), login(1), printf(1), test(1),
 getopt(3), passwd(5), environ(7), sysctl(8)
HISTORY
 dash is a POSIX-compliant implementation of /bin/sh that aims to be as
 small as possible. dash is a direct descendant of the NetBSD version of
 ash (the Almquist SHell), ported to Linux in early 1997. It was renamed
 to dash in 2002.
BUGS
 Setuid shell scripts should be avoided at all costs, as they are a sig-
 nificant security risk.
 PS1, PS2, and PS4 should be subject to parameter expansion before being
 displayed.
BSD January 19, 2003 BSD