SH

NAME

SYNOPSIS

DESCRIPTION

Definitions

Commands

A pipeline is a sequence of one or more commands separated by | (or, for historical compatibility, by ^). The standard output of each command but the last is connected by a pipe(2) to the standard input of the next command. Each command is run as a separate process; the shell waits for the last command to terminate. The exit status of a pipeline is the exit status of the last command.

A list is a sequence of one or more pipelines separated by ;, & (OS/2 only), &&, or ||, and optionally terminated by ; or & (OS/2 only). Of these four symbols, ; and & have equal precedence, which is lower precedence than that of && and ||. The symbols && and || also have equal precedence. A semicolon (;) causes sequential execution of the preceding pipeline; an ampersand (&) causes asynchronous execution of the preceding pipeline (i.e., the shell does not wait for that command to finish. This option is only available under OS/2 and is restricted to single commands and not pipelines because of the differences in the UNIX and OS/2 process models). The symbol && (||) causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) exit status. An arbitrary number of new-lines may appear in a list, instead of semicolons, to delimit commands.

A command is either a simple-command or one of the following. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command.

for name [ in word ... ] do list done

Each time a for command is executed, name is set to the next word taken from the in word list. If in word ... is omitted, then the for command executes the do list once for each positional parameter that is set (see Parameter Substitution below). Execution ends when there are no more words in the list.

select name [ in word ... ] do list done

A select command prints on standard error (file descriptor 2), the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters are used instead (see Parameter Substitution below). The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed words, then the value of the parameter name is set to the word corresponding to this number. If this line is empty the selection list is printed again. Otherwise the value of the parameter name is set to null. The contents of the line read from standard input is saved in the parameter REPLY. The list is executed for each selection until a break or end-of-file is encountered.

case word in [ pattern [ |

pattern ] ... ) list ;; ] ... esac A case command executes the list associated with the first pattern that matches word. The form of the patterns is the same as that used for file-name generation (see File Name Generation) except that a slash, a leading dot, or a dot immediately following a slash need not be matched explicitly, and the match is case sensitive.

if list then list [ elif list then list ] ... [ else list ] fi

The list following if is executed and, if it returns a zero exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is zero, the list following the next then is executed. Failing that, the else list is executed. If no else list or then list is executed, then the if command returns a zero exit status.

while list do list done

A while command repeatedly executes the while list and, if the exit status of the last command in the list is zero, executes the do list; otherwise the loop terminates. If no commands in the do list are executed, then the while command returns a zero exit status; until may be used in place of while to negate the loop termination test.

(list)

Execute list in a sub-shell. The shell creates a new environment in which to execute the list, but does not fork a sub-shell as a Unix system would. The original environment is restored on completion.

{ list; }

list is simply executed.

[[ expression ]]

Evaluates expression and returns a zero exit status when expression is true. See Conditional Expressions below, for a description of expression. Note that [[ and ]] are keywords and require blanks between them and expression.

function name () { list; }

name () { list; }

Define a function which is referenced by name. The body of the function is the list of commands between { and }. Execution of functions is described below (see Execution).

The following words are only recognized as the first word of a command and when not quoted:

if then else elif fi case esac for while until do done { } [[ ]]  

Comments

Aliasing

Aliasing is performed when scripts are read, not while they are executed. Therefore, for an alias to take effect the alias command has to be executed before the command which references the alias is read.

Aliases are frequently used as a short hand for full path names. An option to the aliasing facility allows the value of the alias to be automatically set to the full pathname of the corresponding command. These aliases are called tracked aliases. The value of a tracked alias is defined the first time the corresponding command is looked up and becomes undefined each time the PATH variable is reset. These aliases remain tracked so that the next subsequent reference will redefine the value.  

Conditional Expressions

-a file

True if file exists.

-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.

-f file

True if file exists and is a regular file.

-g file

True if file exists and has its setgid bit set.

-h file

True if file exists and is a symbolic link.

-k file

True if file exists and has its sticky bit set.

-n string

True if the length of string is non-zero.

-o option

True if the option named is on.

-p file

True if file exists and is a fifo special file or a pipe.

-r file

True if file exists and is readable.

-s file

True if file exists and has a size greater than zero.

-t [ fildes ]

True if the open file whose file descriptor number is fildes (1 by default) is associated with a terminal device.

-u file

True if file exists and has its setuid bit set.

-w file

True if file exists and is writable.

-x file

True if file exists and is executable. If file exists and is a directory, then the current process has permission to search in the directory.

-z string

True if the length of string is zero.

-L file

True if file exists and is a symbolic link.

-O file

True if file exists and is owned by the effective user id of this process.

-G file

True if file exists and is owned by the effective user group of this process.

-S file

True if file exists and is a socket.

file1 -nt file2

True if file1 is newer than file2. True if file1 exists and is newer than file2.

file1 -ot file2

True if file1 exists and is older than file2.

file1 -ef file2

True if file1 and file2 and refer to the same file.

s1 = s2

True if strings s1 and s2 are identical.

s1 != s2

True if strings s1 and s2 are not identical.

s1 < s2

True if string s1 comes before s2 are based on the ASCII value of their characters.

s1 > s2

True if string s1 comes after s2 are based on the ASCII value of their characters.

n1 -eq n2

True if n1 is equal to n2.

n1 -ne n2

True if n1 is not equal to n2.

n1 -lt n2

True if n1 is less than to n2.

n1 -gt n2

True if n1 is greater than to n2.

n1 -le n2

True if n1 is less than or equal to n2.

n1 -ge n2

True if n1 is greater than or equal to n2.

Not all of the above have meaning under MSDOS or OS/2. In such cases, the appropriate value is set (false, except for -O and -G).

A compound expression can be constructed from these primitives by using any of the following, listed in decreasing order of precedence.

( expr )

True, if expr is true. Used to group expressions.

! expr

True, if expr is false.

expr1 && expr2

True, if expr1 and expr2 are both true.

expr1 || expr2

True, if expr1 or expr2 is true.

Tilde Substitution

Command Substitution

Parameter Substitution

name = value [ name = value ] ...

Pattern-matching is not performed on value. There cannot be a function and a variable with the same name.

Alternatively, named parameters can be assigned values and attributes by using the typeset special command.

${parameter}

The value, if any, of the parameter is substituted. The braces are required only when parameter is followed by a letter, digit, or underscore that is not to be interpreted as part of its name. If parameter is * or @, all the positional parameters, starting with $1, are substituted (separated by spaces). Parameter $0 is set from argument zero when the shell is invoked.

${#parameter}

If parameter is * or @, the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted.

${parameter:-word}

If parameter is set and is non-null, substitute its value; otherwise substitute word.

${parameter:=word}

If parameter is not set or is null set it to word; the value of the parameter is substituted. Positional parameters may not be assigned to in this way.

${parameter:?word}

If parameter is set and is non-null, substitute its value; otherwise, print word and exit from the shell. If word is omitted, the message ``parameter null or not set´´ is printed.

${parameter:+word}

If parameter is set and is non-null, substitute word; otherwise substitute nothing.

${parameter#pattern}

${parameter##pattern} If the Shell pattern matches the beginning of the value of parameter, then the value of this substitution is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the latter form the largest matching pattern is deleted.

${parameter%pattern}

${parameter%%pattern} If the Shell pattern matches the end of the value of parameter, then the value of this substitution is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the latter form the largest matching pattern is deleted.

In the above, word is not evaluated unless it is to be used as the substituted string, so that, in the following example, pwd is executed only if d is not set or is null:

echo ${d:-`pwd`}

If the colon (:) is omitted from the above expressions, the shell only checks whether parameter is set or not (It is not clear what this means).

The following parameters are automatically set by the shell:

#

The number of positional parameters in decimal.

-

Flags supplied to the shell on invocation or by the set command.

?

The decimal value returned by the last synchronously executed command.

$

The process number of this shell.

!

The process number of the last background command invoked.

_

The last argument of the previous command.

~

The shell reserves all variables beginning with a ~ for its own internal use and these variables cannot be accessed by the user.

The following parameters are used by the shell:

CDPATH

The search path for the cd command. (Note that because a colon is used by MSDOS to indicate a drive, a semi-colon is used to separate the path names instead of a colon - this implies that the CDPATH variable must be set using single or double quotes to surround the value).

COLUMNS

This variable is contains the number of columns on the screen. Currently, the shell only sets the variable in interactive mode, if it is not already set.

COMSPEC

When the shell has to process an MSDOS .bat or OS/2 .cmd file, it expects the file indicated by the value of this environment variable to be an executable program capable of processing the MSDOS .bat or OS/2 .cmd file. The program is invoked with the arguments /c file_name.

ENV

If this parameter is set, then parameter substitution is performed on the value to generate the pathname of the script that will be executed when the shell is invoked (See Invocation below). This file is typically used for alias and function definitions.

EXTENDED_LINE

This parameter pointers to a file which contains information for the shell about how command lines are to be built for particular external programs and how to convert from the format entered to the shell (see Command Line Building).

FCEDIT

The default editor name for the fc command.

HISTFILE

The file where command history is saved across login sessions. The default value is $HOME/history.sh.

HOME

The default argument (home directory) for the cd command.

IFS

Internal field separators, normally space, tab, and new-line.

LINES

This variable is contains the number of lines on the screen. Currently, the shell only sets the variable in interactive mode, if it is not already set.

MAIL

If this parameter is set to the name of a mail file and the MAILPATH parameter is not set, the shell informs the user of the arrival of mail in the specified file.

MAILCHECK

This parameter specifies how often (in seconds) the shell will check for the arrival of mail in the files specified by the MAILPATH or MAIL parameters. If set to 0, the shell will check before each prompt.

MAILPATH

A semi-colon (;) separated list of file names. If this parameter is set, the shell informs the user of the arrival of mail in any of the specified files. Each file name can be followed by % and a message that will be printed when the modification time changes. The default message is "you have mail".

OLDPWD

The previous working directory set by the cd command.

PATH

The search path for commands (see Execution below). The user may not change PATH if executing under rsh. (Note that because a colon is used by MSDOS to indicate a drive, a semi-colon is used to separate the path names instead of a colon - this implies that the PATH variable must be set using single or double quotes to surround the value). The Shell automatically converts Unix format PATH assignments to MSDOS format when appropriate. A assignment is converted if there are no semi-colons, no \s and one or more colons. If there is only one colon, it must not be the second character of the new value.

PWD

The present working directory set by the cd command.

PS1

Primary prompt string, by default ``$ ´´.

PS2

Secondary prompt string, by default ``> ´´.

PS3

Selection prompt string used within a select loop, ``#? ´´.

PS4

The value of this parameter is expanded for parameter substitution and precedes each line of an execution trace. If omitted, the execution trace prompt is ``+ ´´.

RANDOM

Each time this parameter is referenced, a random integer is generated. The sequence of random numbers can be initialized by assigning a numeric value to RANDOM.

REPLY

This parameter is set by the select statement and by the read special command when no arguments are supplied.

SECONDS

Each time this parameter is referenced, the number of seconds since shell invocation is returned. If this parameter is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment.

SHELL

When the shell is invoked, it scans the environment (see Environment below) for this name. If it is found and there is an 'r' in the file name part of its value, the shell becomes a restricted shell. The shell also uses this variable to decide which program to spawn to interpret shell scripts (see Execution below).

TMP

The location of temporary files created by the shell. If this variable is not defined, the Shell uses the HOME directory for temporary files. Failing that, the root directory of the current drive is used.

The shell gives default values to PATH, PS1, PS2, SHELL, HOME and IFS.  

Arithmetic Expansion

Blank Interpretation

File Name Generation

*

Matches any string, including the null string.

?

Matches any single character.

[ ... ]

Matches any one of the enclosed characters. A pair of characters separated by - matches any character lexically between the pair, inclusive. If the first character following the opening ``[´´ is a ``!´´ any character not enclosed is matched.

If the shell has to open or create the file /dev/tty or /dev/null (which are Unix special files), they are converted to the equivalent MSDOS file names (/dev/con and /dev/nul respectively). Any user programs which could expect /dev/tty or /dev/null as arguments must do its own mapping to the MSDOS equivalents.  

Quoting

; & ( ) | ^ < > new-line space tab

A character may be quoted (i.e., made to stand for itself) by preceding it with a \. The pair \new-line is ignored. All characters enclosed between a pair of single quote marks (´´), except a single quote, are quoted. Inside double quote marks (""), parameter and command substitution occurs and \ quotes the characters \, `, ", and $. "$*" is equivalent to "$1 $2 ...", whereas "$@" is equivalent to "$1" "$2" ....  

Arithmetic Evaluation

An arithmetic expression uses nearly the same syntax precedence, and associatively of expression as C. The following set of operators, listed in order of decreasing precedence, have been implemented:

- + ! ~ ++ --	unary minus/plus, logical NOT, complement, {pre, post}{in,de}crement
&	Logical AND
^	Logical XOR
|	Logical OR
* / %	multiplication, division, remainder
+ -	addition, subtraction
<< >>	Logical shift left and right
<= >= < >	comparison
== !=	equality inequality
&&	Logical AND
|| ^^	Logical OR, XOR
? :	Ternary operator
= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^=	assignement

The operators &&, ||, &&= and ||= are short-circuiting and only one of the latter two expressions in a ternary operator is evaluated. Note the precedence of the logical AND, XOR and OR operators.

Sub-expressions in parentheses () are evaluated first and can be used to override the above precedence rules.

Named parameters can be reference by name within an expression without using the parameter substitution symtax.

Since many of the arithmetic operators require quoting, an alternative form of the let command is provided. For any command which begins with a ((, all the characters until a matching )) are treated as a quoted expression. More precisely, ((...)) is equivalent to let "...".  

Prompting

Many people like to have the shell provide them with useful information in their prompt. To accommodate this, the shell recognises special sequences of characters in the values of PS1 and PS2, and substitutes the appropriate information for them. The special sequences and what they signify are:

%d

Place the current date, in the form DAY DD-MM-YY into the prompt.

%e

Place the current event number (as defined by the history command) into the prompt. If history evaluation has been turned off (via history -d), no number will be substituted in (i.e. the %e will be removed).

%n

Place the current working drive into the prompt.

%p

Place the current working directory into the prompt.

%t

Place the current time of day, in the form HH:MM into the prompt. The time is on a 24 hour clock, i.e. 1:30 in the afternoon will be 13:30.

%v

Place the MSDOS version number, in the form MSDOS MM:MM into the prompt.

%%

Place the character % into the prompt.

\xxx

Place the character \xxx into the prompt. The processing of escape sequences is the same as that for echo.

Some of these facilities are of more use than others.  

Input/Output

<word

Use file word as standard input (file descriptor 0).

>word

Use file word as standard output (file descriptor 1). If the file does not exist it is created; otherwise, it is truncated to zero length.

>>word

Use file word as standard output. If the file exists output is appended to it (by first seeking to the end-of-file); otherwise, the file is created.

<<[-]word

The shell input is read up to a line that is the same as word, or to an end-of-file. The resulting document becomes the standard input. If any character of word is quoted, no interpretation is placed upon the characters of the document; otherwise, parameter and command substitution occurs, (unescaped) \new-line is ignored, and \ must be used to quote the characters \, $, `, and the first character of word. If - is appended to <<, all leading tabs are stripped from word and from the document.

<&digit

Use the file associated with file descriptor digit as standard input. Similarly for the standard output using >&digit.

<&-

The standard input is closed. Similarly for the standard output using >&-.

n<>word

causes the file word to be opened on file descriptor n for both reading and writing. The file must already exist.

If any of the above is preceded by a digit, the file descriptor which will be associated with the file is that specified by the digit (instead of the default 0 or 1). For example:

... 2>&1

associates file descriptor 2 with the file currently associated with file descriptor 1.

The order in which redirections are specified is significant. The shell evaluates redirections left-to-right. For example:

... 1>xxx 2>&1

first associates file descriptor 1 with file xxx. It associates file descriptor 2 with the file associated with file descriptor 1 (i.e. xxx). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and file descriptor 1 would be associated with file xxx .

The environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications.

Redirection of output is not allowed in the restricted shell.  

Environment

The environment for any simple-command may be augmented by prefixing it with one or more assignments to parameters. Thus:

TERM=450 cmd args                      and

(export TERM; TERM=450; cmd args)

are equivalent (as far as the execution of cmd is concerned).

If the -k flag is set, all keyword arguments are placed in the environment, even if they occur after the command name. The following first prints a=b c and c:

echo a=b c
set -k
echo a=b c

Signals

Command Re-entry

History

! [ ! | str | num ] terminator

!! will place the previous command in the command line. !num will place the history command with the specified number in the command line. !str will find the most recent command line that started with the characters in str.

The terminator determines what action is performed after the history line has been found. If the original history command is entered using the <return> key, the new command line is passed directly to the shell. If the <end> key is pressed, the new command line can be edited in the manner described below.  

Command Line Editing

Right

Move the cursor right one character

WordRight

Move the cursor right one word

Left

Move the cursor left one character

WordLeft

Move the cursor left one word

Previous

Get the previous command from the history file

Next

Get the next command from the history file

Insert

Toggle insert/overwrite mode (note the shape of the cursor changes to indicate the current mode)

DeleteRight

Delete the current character unless the cursor is at the end of line when no action is taken

Start

Move the cursor to the start of the command

Complete

Attempt to complete the filename. The shell attempts to complete the file name at the current cursor position. The file name is delimited by white space characters. If the shell is unable to complete the file name (ie no match can be found in the appropriate directory), the bell is rung. If a single match is found, the new file name is displayed. If multiple matches are found, the file name is replaced by the longest non-unique part of the file name and the bell is rung.

End

Move the cursor to the end of the command, unless the first character of the command is a !, in which case the appropriate history search is done. The cursor is placed at the end of the command line.

Flush

Delete to the end of the line

ScanBackward

Search backwards from the current history command for the next match against the last history request or the string currently in the command line if there has been no previous history request.

ScanForeward

Search forewards from the current history command for the next match against the last history request or the string currently in the command line if there has been no previous history request.

Clear

Erase the complete line.

Directory

Display the file name list matching the partially entered file name under the cursor. If no matches are found the bell is rung. To display the whole directory, enter the directory name followed by a slash /. After the directory listing has been displayed, the entered command line is redisplayed.

DeleteLeft

Delete the character to the left of the cursor.

Return

Execute the command line, unless the first character of the command is a !, in which case the appropriate history processing is done. This is the actual key pressed and cannot be modified by the initialisation file.

Initialisation File

For the keyboard entries, the numeric values give the MSDOS Function 8 (Console Input without Echo) return values for that entry. Note that extended codes (function keys) require two calls to this function. The first call returns zero and the second the extended code. In the configuration file, a first numeric value of zero indicates a extended code and must be followed by a second value. A non-zero first numeric value must not be followed by anything else on the line.

Other entries must only have one numeric value. A zero value disables the function and a non-zero value enables the function. At present, there are two other functions:

Bell

Enable/disable warning bells

HalfHeight

Use full or halfheight block cursor to indicate Insert mode

InsertMode

Set the default insert mode on or off

InsertCursor

Enable/disable the insert mode cursor.

Invalid lines or lines beginning with a # are ignored.

The following table gives the list of valid keywords and their default values:

Keyword
_
KEYBOARD ENTRIES
ScanBackward	0	0x49	PAGE UP
ScanForeward	0	0x51	PAGE DOWN
Previous	0	0x48	UP ARROW
Next	0	0x50	DOWN ARROW
Left	0	0x4b	LEFT ARROW
Right	0	0x4d	RIGHT ARROW
WordRight	0	0x74	Control RIGHT ARROW
WordLeft	0	0x73	Control LEFT ARROW
Start	0	0x47	HOME
Clear	0	0x76	Control PAGE DOWN
Flush	0	0x75	Control END
End	0	0x4f	END
Insert	0	0x52	INSERT
DeleteRight	0	0x53	DELETE
DeleteLeft	0x08		BACKSPACE
Complete	0	0x77	Control HOME
Directory	0	0x0f	Shift TAB
_
OTHER FUNCTIONS
Bell	0
HalfHeight	0
InsertMode	0
InsertCursor	1

 

Execution

The shell parameter PATH defines the search path for the directory containing the command. Alternative directory names are separated by a semi-colon (;). The default path is ;c:/bin;c:/usr/bin (specifying the current directory, c:/bin, and c:/usr/bin, in that order). Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the semi-colon delimiters anywhere else in the path list. If the command name contains a / or starts with x: (where x is a drive letter) the search path is not used; such commands will not be executed by the restricted shell. Otherwise, each directory in the path is searched for an executable file. Executable files are indicated by a .exe or .com extension. This extension is automatically supplied by the shell and not have to be entered by the user.

If the file with a .com or .exe extension cannot be found in the directory, the file is opened and first 512 characters are read. If there are no characters in the block with a value in the range 0 to 7, the file is assumed to be a script file containing shell commands. Note that the shell will check the file and if that file does not exist or is not a script, it will try the file with an extension of .sh. If a .sh file is found, that will be processed. A sub-shell (given by the environment variable SHELL) is spawned to read it.

If the script file starts with the a line of the form #! interpreter [arguments], the interpreter is invoked instead of the shell to process the script. Optional arguments can be supplied in the script file which are passed before the name of the script file. Thus, if the file demo contained the following string as the first line

#! perl -sP

Entering demo name would be equivalent to entering the perl -sP name at the command prompt. Note that no other processing of the first line other that the separation (by white space) into arguments is done.

If none of the above conditions for a executable file are detected and a file with a .bat extension exists in the directory, the command processor given by the COMSPEC environment variable is spawned to process the file. This is normally the standard MSDOS command.com or OS/2 cmd.exe processor.

A parenthesized command is also executed in a sub-shell.  

Command Line Building

The file is scanned prior to the execution of an external command. An entry in this file is contained in a single line and consists of a program name (in upper or lower case), white space, an equals symbol, white space and the program type followed by up to four optional values, followed by an end of line character. The value tells the shell how to build the command line and the optional values provide additional information. The valid program types are (note that invalid entries cause a line to be ignored) given below. These program types must appear as the first value following the equals. Otherwise, they are ignored. An empty program types may be empty to only select one or more of the optional values.

unix

This program can process the command line using the indirect command file character @. When a program, which can process this format, finds a command line parameter starting with a @ in the command line, it treats the rest of the parameter as a file and reads the command line parameters from that file (one per line, the end of line characters can be escaped by preceeding with a \). Examples of this functionality include the Standard Linker and Librarian.

The file name is set up in UNIX format (using / as the directory separators).

This functionality allows the user to get round the 127 byte command line length limit of MSDOS. A sample version of the code to process wild cards and indirect command files is included with the source of the shell in the file stdargv.c.

dos

This program can process the command line using the indirect command file character @. The file name is set up in DOS format (using \s as the directory separators).

environ

The command line is passed to the external program in the environment variable specified by the first optional value. The optional second value which is numeric, gives the parameter separator character to be used (see strtol for valid formats where base parameter is zero). If this second value is missing or evaluates to zero, space is used.

The following optional values described below may be used after either unix or dos or by themselves:

switch

The optional value switch causes the program parameters to be converted from UNIX format to MSDOS format. This means that parameters beginning with an - have it converted to a /. For all other parameters, /s are converted to \s. This option is not applied to quoted parameters or escaped characters.

This functionality allows ease of entry of MSDOS commands which expect MSDOS directory separators which the shell interpretes as the escape character (not that the underlying MSDOS really cares). export The optional value export causes the marked environment variables to be converted from UNIX format to MSDOS format. This is equivalent to setting the -m flag for this program only.

noexpand

The optional value noexpand disables file name generation when building the command line (also see set command).

noswap

The optional value noswap disables swapping for the command. This may speed up the execution of small commands.

Functions

Functions execute in the same process as the caller and share all files and present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate and the condition to be passed on to the caller. A trap set on EXIT inside a function is executed after the function completes.

Ordinarily, variables are shared between the calling program and the function. However, the typeset special command used within a function defines local variables whose scope includes the current function and all functions it calls.

The special command return is used to return from function calls. Errors within functions return control to the caller.

Function identifiers can be listed with the function special command. The text of functions will also be listed. Function can be undefined with the unfunction special command.

Ordinarily, functions are unset when the shell executes a shell script. Functions that need to be defined across separate invocations of the shell should be placed in the ENV file.  

Special Commands

:

No effect; the command does nothing. A zero exit code is returned.

letter:

Select the drive specified by letter.

. file

Read and execute commands from file and return. The search path specified by PATH is used to find the directory containing file.

alias [ -t ] [ name[=value ] ... ]

Alias with no arguments prints the list of aliases in the form name=value on standard output. An alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution. The -t flag is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remained tracked. Without the -t flag, for each name in the argument list for which no value is given, the name and value of the alias is printed. Alias returns zero unless a name is given for which no alias has been defined.

break [ n ]

Exit from the enclosing for or while loop, if any. If n is specified, break n levels.

builtin [ args ... ]

Force the selection of the builtin version of a command. The builtin shell command selected by the first args value is executed with the parameters defined by the remaining argss. If no arguments are given, a list of all builtin commands is printed.

If the first argument is one of the following, the processing of the builtin command in the following arguments are changed as indicated:

-a

Set the following builtin commands to use builtin version in preference to any function or external versions.

-d

Set the following builtin commands to use the function or external version in preference to the builtin version.

-s

Display the current status of the following builtin commands.

continue [ n ]

Resume the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

cd [ arg ]

cd search replace

This command can be in either of two forms. In the first form it changes the current directory to arg. The shell parameter HOME is the default arg. The shell parameter CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a semi-colon (;). The default path is <null> (specifying the current directory). Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the semi-colon delimiters anywhere else in the path list. If arg begins with a / or x: (where x is a drive letter), the search path is not used. Otherwise, each directory in the path is searched for arg. The cd command may not be executed by rsh.

In the second form, cd substitutes the string replace for the string search in the current directory name, PWD and tries to change to this new directory.

detach program [ args ]

This command (which is only available under OS/2) starts and simultaneously detaches an OS/2 program from the shell. Any program that is started with detach command must be able to process independently outside the control of the shell. Builtin shell commands and functions cannot be detached.

echo [ arg ... ]

Echo arguments. Echo writes its arguments separated by blanks and terminated by a new-line on the standard output. It also understands C-like escape conventions; beware of conflicts with the shell's use of \:

\b

backspace

\c

print line without new-line

\f

form-feed

\n

new-line

\r

carriage return

\t

tab

\v

vertical tab

\\

backslash

\n

the 8-bit character whose ASCII code is the 1-, 2- or 3-digit octal number n, which must start with a zero.

Echo is useful for producing diagnostics in command files and for sending known data into a pipe.

eval [ arg ... ]

The arguments are read as input to the shell and the resulting command(s) executed.

exec [ arg ... ]

The command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may appear and, if no other arguments are given, cause the shell input/output to be modified.

exit [ n ]

Causes a shell to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an end-of-file will also cause the shell to exit.)

export [ name[=value] ... ]

The given names are marked for automatic export to the environment of subsequently-executed commands. If no arguments are given, a list of all names that are exported in this shell is printed. Function names may not be exported.

false

No effect; the command does nothing. A non-zero exit code is returned.

fc [ -e EditorName ] [ -nlr ] [ First [ Last ] ]

fc -e - [ Old=New ] [ Command ]

In the first form, a range of commands from First to Last is selected from the last 100 commands that were typed at the terminal. The First and Last parameters can be specified as a number or as a string. A string locates the most recent command starting with the given string. A negative number is used as an offset to the current command number. If Last is not specified, then it is set to First. If First is not specified, the default is the previous command for editing and -16 for listing.

-l

Lists the commands to standard output.

-r

Reverses the order of the commands in the list.

-n

Suppresses command numbers when listing.

If the -l flag is not specified, the editor program specified by EditorName is invoked on a file containing these key-board commands. If EditorName is not supplied, then the value of the FCEDIT parameter is used as the editor. When editing is complete, the edited command(s) is executed.

In the second form, the specified command is carried out again after the Old=New substitution is performed.

functions [ name ... ]

The functions given by names are printed. If no arguments are given, a all the functions are displayed.

getopt optstring name [ args ... ]

Parse command options and write them to standard output. Getopt is used to break up options in command lines for easy parsing by shell procedures and to check for legal options. Optstring is a string of recognized option letters (see getopt(3C)); if a letter is followed by a colon, the option is expected to have an argument which may or may not be separated from it by white space. The special option -- is used to delimit the end of the options. If it is used explicitly, getopt will recognize it; otherwise, getopt will generate it; in either case, getopt will place it at the end of the options. Each option is preceded by a - and is in its own positional parameter; each option argument is also parsed into its own positional parameter.

The following code fragment shows how one might process the arguments for a command that can take the options a or b, as well as the option o, which requires an argument:

then
     echo $USAGE
     exit 2
fi
for i in $*
do
     case $i in
     -a | -b)  FLAG=$i; shift;;
     -o)       OARG=$2; shift 2;;
     --)       shift; break;;
     esac
done

This code will accept any of the following as equivalent:

cmd -aoarg file file
cmd -a -o arg file file
cmd -oarg -a file file
cmd -a -oarg -- file file

history [ -deils ]

The history command, with no arguments, will print all the commands that are currently saved in the shell's history buffers. As new commands are executed, and space in the buffers runs out, old commands will be deleted. The history commands prints out the stored commands with sequence numbers. Negative numbered commands, through command number zero, are commands that were retrieved from the saved history file. Commands starting at one were entered during the current login session. If a saved command contains embedded newlines, these will be printed out as the sequence \n, so that individual command stay on one line.

The arguments changes the way the shell processes history information as follows:

-d

Disable the saving of commands in the history file.

-e

Enable the saving of commands in the history file.

-i

Initialise the history file.

-l

Load the history from the file given by the HISTFILE environment variable.

-s

Save the history to the file given by the HISTFILE environment variable.

jobs [ -l ]

This command (which is only available under OS/2) lists the active jobs; giving the -l options lists process id's in addition to the normal information.

kill [ -sig ] process ...

This command (which is only available under OS/2) sends either the TERM (terminate) signal or the specified signal to the specified processes. Signals are given by name, which are listed by 'kill -l'.

let [ arg ... ]

Each arg is an arithmetic expression to be evaluated. All calculations are done as long integers and no check for overflow is performed. See Arithmetic Evaluation above for a description of arithmetic expressions..

The return code is 0 if the value of the last expression is non-zero, and 1 otherwise.

msdos [ name[=value] ... ]

The given names are marked msdos format and if the -m flag is set, the values of the these names are exported to child processes with any slashes in the value replaced by \s. If no arguments are given, a list of all msdos names is printed.

print [ -Rnprs ] [ -u unit ] [ args ... ]

The shell output mechanism. With no flags or with flag - or -- the args are printed on standard output as described by the echo command.

-R

Prints in the raw mode, in which the escape conventions of the echo command are ignored. The -R option prints all subsequent args and options other than -n.

-n

Prevents a new-line from being added to the output.

-p

-p flag has not effect and is defined for compatability.

-r

Prints in the raw mode, in which the escape conventions of the echo command are ignored.

-s

Writes the args to the history file instead of to standard output.

-u unit

Specifies a one digit file descriptor unit number on which the output is placed. The default is 1.

pwd [ drive ... ]

Print the current working directory. If drive is present, the current working directory on each of the drives is printed. drive contains a string of drive letters, no colons are required.

read [ -prs ] [ -u unit ] [ name?prompt ] [ name ... ]

The shell input mechanism. One line is read and is broken up into words using the characters in IFS as separators. In raw mode, -r, a \ at the end of a line does not signify line continuation. The first word is assigned to the first name, the second word to the second name, etc., with leftover words assigned to the last name. If the -s flag is present, the input will be saved as a command in the history file. The -p flag has not effect and is defined for compatability. The flag -u can be used to specify a one digit file descriptor unit to read from. The file descriptor can be opened with the exec special command. The default value of unit is 0. If name is omitted then REPLY is used as the default name. If the first argument contains a ?, the remainder of this word is used as a prompt when the shell is interactive. If the given file descriptor is open for writing and is a terminal device then the prompt is placed on this unit. Otherwise the prompt is issued on file descriptor 2. The return code is 0 unless an end-of-file is encountered.

readonly [ name[=value] ... ]

The given names are marked readonly and the values of the these names may not be changed by subsequent assignment. If no arguments are given, a list of all readonly names is printed.

return [ n ]

Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed.

set [ [-|+]aefkmntuvx ] [ -o option ] [ arg ... ]

-a

Mark variables which are modified or created for export.

-e

Exit immediately if a command exits with a non-zero exit status.

-f

Disable file name generation

-k

All keyword arguments are placed in the environment for a command, not just those that precede the command name.

-m

For those variables marked as msdos variables, the values are exported to child processes with the slashes replaced by \s. Most MSDOS utilities do not care if a file name contains a slash or \ as a directory separator. However, some like the linker require \s in the value of the LIB variable.

-n

Read commands but do not execute them.

-o option

The argument that follows this option can be one of the following option names:

allexport

Same as -a.

bell

Enable alarm bell on errors

errexit

Same as -e.

halfheight

Set cursor to halfheight when in insert mode. If off, a full height cursor is used.

ignoreeof

The shell will not exit on end-of-file. The command exit must be used.

insertmode

Set the default edit mode to insert rather than overwrite.

keyword

Same as -k.

markdirs

Appends a / (slash) to all directory names that are a result of file name substitution.

noclobber

Prevents redirection > from truncating existing files. A vertical bar must follow the redirection symbol (>|) to truncate a file when this option is turned on.

noexec

Same as -n.

noglob

Same as -f.

nounset

Same as -u.

privileged

Same as -p.

trackall

Same as -h.

verbose

Same as -v.

xtrace

Same as -x.

-t

Exit after reading and executing one command.

-u

Treat unset variables as an error when substituting.

-v

Print shell input lines as they are read.

-x

Print commands and their arguments as they are executed.

--

Do not change any of the flags; useful in setting $1 to -.

Using + rather than - causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags may be found in $-. The remaining arguments are positional parameters and are assigned, in order, to $1, $2, .... If no arguments are given the values of all names are printed.

shift [ n ]

The positional parameters from $n+1 ... are renamed $1 .... If n is not given, it is assumed to be 1.

start [ -dfiCWPF ] [ -t title ] [ program [ arguments.. ] ]

This command (which is only available under OS/2) starts an OS/2 program in a new session. If no program and arguments parameters are entered, the shell is started unless the -C option has been used to select the OS/2 command processor.

The arguments changes the way the shell starts the session as follows:

-d

Normally, command are started by invoking the shell in the new session. This option invokes the command directly.

-f

The program becomes the foreground session. If this parameter is not specified, the program becomes a background session.

-i

The new session will inherit the original environment of the shell instead of the current environment.

-t title

Sets the title of the new session.

-F

This application is a full-screen application that must run in a separate session independent of Presentation Manager.

-W

This is an OS/2 application that runs within a Presentation Manager window.

-P

This application is started as a Presentation Manager application.

-C

Use the OS/2 command processor instead of the shell.

swap [ options ]

This command (which is only available under MS-DOS) defines how the shell will handle swapping itself to reduce its memory requirements whilst other programs execute. The options are

off

Disable swapping. The shell remains in memory whilst the child is running and reduces the available memory by about 200K (depending on the size of the environment and history).

on

Enable all devices. The shell will swap out to either expanded or extended memory or to disk, execute the command and then swap back in. Whilest swapped, the shell reduces the available memory by about 3K.

expand

Enable swapping to Expanded Memory. The EMS driver must exist on your system for this to work.

extend [ start address ]

Enable swapping to Extended Memory. If you have an XMS driver on your system, the shell will use the XMS driver. Otherwise, the BIOS Interrupt 15 interface is used. The optional start address defines the based address in the Extended Memory at which point the shell writes its swap area when the BIOS interface is used. The default location is 0x100000.

disk

Enable swapping to disk. The shell creates a temporary file and saves itself in it. On completion, the file is deleted. This is the slowest method of swapping.

With no options, the current swapping options are displayed.

test expr or [ expr ]

Evaluate conditional expressions. Test evaluates the expression expr and, if its value is true, returns a zero (true) exit status; otherwise, a non-zero (false) exit status is returned; test also returns a non-zero exit status if there are no arguments. The primitives are the same as for the [[ expression ]] command, except that -a and -o are not primitives, but are used to combine operators (see test (1)). -a is the binary and operator and -o is the binary or operator.

Notice that all the operators and flags are separate arguments to test. Notice also that parentheses are meaningful to the shell and, therefore, must be escaped.

trap [ arg ] [ SignalNumber ] ...

The command arg is to be read and executed when the shell receives signal(s) SignalNumber. (Note that arg is scanned once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. If arg is absent all trap(s) SignalNumber are reset to their original values. If arg is the null string this signal is ignored by the shell and by the commands it invokes. If SignalNumber is DEBUG then arg will be executed after each command. If SignalNumber is ERR, arg will be executed whenever a command has a non-zero exit code. If SignalNumber is 0 or EXIT and the trap statement is executed inside the body of a function, the command arg is executed after the function completes. If SignalNumber is 0 or EXIT for a trap set outside any function, the command arg is executed on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.

true

No effect; the command does nothing. A zero exit code is returned.

typeset [ -HLRZfilprtux[n] [ name[ =value ] ] ... ]

When invoked inside a function, a new instance of the parameter name is created. The parameter value and type are restored when the function completes. The following list of attributes may be specified:

-H

This flag provides UNIX to host-name file mapping on non-UNIX machines (see msdos command).

-L

Left justify and remove leading blanks from value. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment. When the parameter is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z flag is also set. The -R flag is turned off.

-R

Right justify and fill with leading blanks. If n is non-zero, it defines the width of the field, otherwise it is determined by the width of the value of first assignment. The field is left filled with blanks or truncated from the end if the parameter is reassigned. The -L flag is turned off.

-Z

Right justify and fill with leading zeros if the first non-blank character is a digit and the -L flag has not been set. If n is non-zero, it defines the width of the field, otherwise it is determined by the width of the value of first assignment.

-f

The names refer to function names rather than parameter names. No assignments can be made and the only other valid flags are -t, which turns on execution tracing for this function and -x, to allow the function to remain in effect across shell procedures executed in the same process environment.

-i

Parameter is an integer. This makes arithmetic faster. If n is non-zero it defines the output arithmetic base, otherwise the first assignment determines the output base.

-l

All upper-case characters converted to lower-case. The upper-case flag, -u is turned off.

-p

The output of this command, if any, is written onto the two-way pipe. This option has no effect in the Shell.

-r

The given names are marked readonly and these names cannot be changed by subsequent assignment.

-t

Tags the named parameters. Tags are user definable and have no special meaning to the shell.

-u

All lower-case characters are converted to upper-case characters. The lower-case flag, -l is turned off.

-x

The given names are marked for automatic export to the environment of subsequently-executed commands.

Using + rather than - causes these flags to be turned off. If no name arguments are given but flags are specified, a list of names (and optionally the values) of the parameters which have these flags set is printed. (Using + rather than - keeps the values to be printed.) If no names and flags are given, the names and attributes of all parameters are printed.

umask [ nnn ]

The user file-creation mask is set to nnn (see umask(2)). If nnn is omitted, the current value of the mask is printed.

unalias name ...

The aliases given by the list of names are removed from the alias list.

unfunction name ...

For each name, remove the corresponding function.

unset [ -f ] name ...

The parameters given by the list of names are unassigned (their values and attributes are erased). The following variables, as well as those with a read-only attribute cannot be unset: PATH, PS1, PS2, and IFS. If the -f flag is set, then the names refer to function names and the functions are removed.

ver

Display the current version of the shell.

whence [ -pv ] [ name ... ]

type [ -p ] [ name ... ]

For each name specified, indicate how it would be interpreted if used as a command name. Note that type is a shorthand for whence -v.

-p

Does a path search for name even if the name is an alias, a function, or a reserved word.

-v

Produces a more verbose report.

Invocation

-c string

If the -c flag is present commands are read from string.

-s

If the -s flag is present or if no arguments remain commands are read from the standard input. Any remaining arguments specify the positional parameters. Shell output (except for Special Commands) is written to file descriptor 2.

-i

If the -i flag is present or if the shell input and output are attached to a terminal, this shell is interactive. In this case, the TERMINATE signal is ignored and the INTERRUPT signal is caught and ignored. In all cases, the QUIT signal is ignored by the shell.

-r

If the -r flag is present, the shell is a restricted shell.

-0(zero)

If the -0(zero) flag is present, this has the same effect as starting the shell with the first character of argument zero as a - (see above).

-R

If the -R flag is present, the shell is the root shell and cannot be terminated using exit. Under MSDOS, the system must be re-booted. Under OS/2, the shell must be killed by an external program.

The remaining flags and arguments are described under the set command above.  

Rsh Only

Changing directory (see cd(1)),
Setting the value of SHELL, ENV, or $PATH,
Specifying path or command names containing /,
Redirecting output (> and >>).

The restrictions above are enforced after profile.sh and the ENV files are interpreted.

When a command to be executed is found to be a shell procedure, rsh invokes sh to execute it. Thus, it is possible to provide to the end-user shell procedures that have access to the full power of the standard shell, while imposing a limited menu of commands; this scheme assumes that the end-user does not have write and execute permissions in the same directory.

The net effect of these rules is that the writer of the profile.sh has complete control over user actions, by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not the login directory).

The system administrator often sets up a directory of commands (i.e., /usr/rbin) that can be safely invoked by rsh. Some systems also provide a restricted editor red.  

EXIT STATUS

FILES

CRITICAL ERRORS

LIMIITATIONS

Under OS/2, asynchronous commands are supported to a degree. However, this is very limited because of the nature of the forking commands under OS/2 which does not match the UNIX model. This difference has also meant that pipes (as in MS-DOS) are implemented as files and not OS/2 pipes. For more details, see the source code.  

SEE ALSO

ACKNOWLEDGEMENTS

David Korn and Steve Bourne (the original ideas)
Charles Forsyth (the original source for the MINIX Shell program)
Erik Baalbergen (the code for the test function)
Paul Falstad (the code for the maths functions)

In addition, a very large number of people (too many to mention) who have been involved in testing and debugging the program.

Index

NAME

SYNOPSIS

DESCRIPTION

Definitions

Commands

Comments

Aliasing

Conditional Expressions

Tilde Substitution

Command Substitution

Parameter Substitution

Arithmetic Expansion

Blank Interpretation

File Name Generation

Quoting

Arithmetic Evaluation

Prompting

Input/Output

Environment

Signals

Command Re-entry

History

Command Line Editing

Initialisation File

Execution

Command Line Building

Functions

Special Commands

Invocation

Rsh Only

EXIT STATUS

FILES

CRITICAL ERRORS

LIMIITATIONS

SEE ALSO

ACKNOWLEDGEMENTS