for name=Expression Expression statement
next

OR

for name=Expression Expression
statement . . . 
next

OR

for Expression, Expression, Expression statement
next

OR

for Expression, Expression, Expression
statement . . .
next

The first format specifes a single statement where the variable takes on the value of the first expression and then is increased by one on each loop until it exceeds the value of the second expression. You can use the second format to do the same thing , but you can specify a group of statements.

The third format requires an initialization expression followed by a test expression (such as true to continue) and a loop-continuation action expression. You can use the fourth format to do the same thing, but you can specify a group of statements. Use commas to separate the expressions in the third and fourth formats.

fun f ([a, . . . ]) [v, . . . ]
statement . . . 
nuf

f specifies the function name, a specifies any parameters, and v identifies any local variables for the user-written function. You can specify up to 10 parameters and local variables; however, they cannot be arrays or associated with I/O functions. You cannot nest function definitions.

if Expression statement
[else
statement . . . ]
fi

OR

if Expression
statement . . .
 [else
statement . . . ]
fi

The first format specifies a single statement and the second format specifies a group of statements to continue using if the expression evaluates to nonzero. The strings 0 and "" (null) evaluate as zero.

In the second format, an optional else allows a group of statements to be performed when the first group is not. The only statement permitted on the same line with an else is an if. You can put fis only on the same line as another fi. You can combine else and if into elif. You can close an if . . . elif . . . [else . . . ] sequence with a single fi.

onintr Label

OR

onintr

In the first format, control passes to the Label given, just as if a goto had been performed when onintr was executed. The effect of the onintr statement is cleared after each interrupt. In the second format, pressing INTERRUPT ends the bs program.

while Expression statement
next

OR

while Expression
statement . . . 
next

The while statement is similar to the for statement except that only the conditional expression for loop continuation is given.

(False, True) [a == b]

• The end of file
• Result of the eval built-in function
• Return from user-written functions (see freturn)

An interrogation trap (end of file, for example), causes an immediate transfer to the most recent interrogation, possibly skipping assignment statements or intervening function levels.

The result of:

Expression & Expression

is 1 (true) only if both of its parameters are non-zero (true); it is 0 (false) if one or both of its parameters are 0 (false).

The result of:

Expression | Expression

is 1 (true) if one or both of its expressions are non-zero (true); it is 0 (false) only if both of its expressions are 0 (false). Both operators treat a null string as a zero.

• < for less than
• <= for less than or equal to
• > for greater than
• >= for greater than or equal to
• == for equal to
• != for not equal to

The relational operators return 1 if the specified relation is True; otherwise they return 0 (false). Relational operators at the same level extend as follows: a>b>c is the same as a>b& b>c. A string comparison is made if both operands are strings. The comparison is based on the collating sequence specified in the environment variable LC_COLLATE. The National Language Support Overview contains more information on this environment variable.

Note: See ed for a more detailed discussion of this special notation.

.

Matches any character except the new-line character.

*

Matches zero or more occurrences of the pattern element that it follows. For example, .* matches zero or more occurrences of any character except the new-line character.

$

Specifies the end of the line.

[.-.]

Matches any one character in the specified range ([.-.]) or list ([ . . . ]), including the first and last characters.

[^ .-.]

[^ . . . ]

Matches any character except the new-line character and any remaining characters in a range or list. A circumflex (^ ) has this special meaning only when it immediately follows the left bracket.

[].-.]

[] . . . ]

Matches ] or any character in the list. The right square bracket does not terminate such a list when it is the first character within it (after an initial ^ , if any).

\( . . . \)

Marks a substring and matches it exactly.The pattern must match from the beginning of the string and the longest possible string. Consider, for example:

match ('a123ab123',".*\([a-z]\)") = 6

In this instance, .* matches a 123a (the longest string that precedes a character in the range a-z); \ ([a-z]\) matches b , giving a total of six characters matched in the string. In an expression such as [a-z] , the minus means "through," according to the current collating sequence.

A collating sequence may define equivalence classes for use in character ranges. See the "International Character Support Overview" for more information on collating sequences and equivalence classes.

The mstring function returns the nth substring in the last call to match (n must be between 1 and 10 inclusive).

• 0 for standard input
• 1 for standard output
• 2 for error output
• A string representing a file name
• A string beginning with an !, which represents a command to be run (using "sh -c")

Mode must be specified with an r for read, w for write, W for write without the new line character, or a for append. The initial associations are:

• open ("get", 0, "r")
• open ("put", 1, "w")
• open ("puterr", 2, "w")

Since exact table sizes are not defined, the interrogation operator should be used to detect end-of-table; for example:

table("t",100)

               
.
.
.
#If word contains "parity", the following expression
#adds one to the count of that word:
++t[word]
.
.
.
#To display the key/value pairs:
for i = 0, ? (s = item (t, i)), ++i if key( ) put = key
( )_":"_s

name = "x,y,z"
eval("++"_name)

which increments the variable "x,y,z" . In addition, when eval is preceded by ? (interrogation operator), you can control bs error conditions. For example:

?eval ("open(\"X\",\"XXX\", \"r\")")

returns the value zero if there is no file named "XXX" (instead of halting your program). The following performs a goto to the label "L:" (if it exists):

label = "L:"
if! (?eval ("goto"_label))puterr="no label"

The call requests are as follows:

plot(0, term)

Causes further plot output to be piped into tplot with a flag of -Tterm.

plot(1)

Erases the plotter.

plot(2, string)

Labels the current point with string

plot(3, x1, y1, x2, y2)

Draws the line between (x1, y1) and (x2, y2).

plot(4, x, y, r)

Draws a circle with center(x, y) and radius r.

plot(5, x1, y1, x2, y2, x3, y3)

Draws an arc (counterclockwise) with center (x1, y1), and end points (x2,y2) and (x3, y3).

plot(6)

Not implemented.

plot(7, x, y)

Makes the current point at (x, y).

plot(8, x, y)

Draws a line from the current point to (x ,y).

plot(9, x, y)

Draws a point at (x, y).

plot(10, string)

Sets the line mode to string

plot(11, x1, y1, x2, y2)

Makes (x1, y1) the lower left corner of the plotting area and (x2, y2) the upper right corner of the plotting area.

plot(12, x1, y1, x2, y2)

Causes subsequent x(y) coordinates to be multiplied by x1 (y1) and then added to x2 (y2) before they are plotted. The initial scaling is plot(12, 1.0, 1.0, 0.0, 0.0).