| cdp[0] | cnt, the number of elements to concatenate follows the command. |
| sp[0]..sp[1-cnt] | hold reference to the elements to concatenate. |
| sp[0] | points to array |
| sp[-1] | is an expr |
| sp[0] | points to array. |
| cdp[0] | array reference follows the command. |
| sp[0] | points to an array. |
| sp[-1] | is an expression. |
| sp[0] | holds the second value. |
| sp[-1] | holds the first value. |
| sp[0] | is the source expression |
| sp[-1] | points to the target |
| cdp[0] | an array reference follows the command. |
| sp[0] | has an expression, used for the index of a cell in the array. |
| sp[0] | has an expression, used for the index of a cell in the array. |
| sp[0] | is the source expression |
| sp[-1] | points to the target |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| cdp[0] | is a reference to the function block |
| cdp[1] | holds number of input arguments |
| sp[0] | is the second string. |
| sp[-1] | is the first string. |
| sp[0] | holds the expression identifying the file to close |
| sp[0] | is the value. |
| sp[0] | is the array to delete. |
| sp[0] | is the second value. |
| sp[-1] | is the first value. |
| sp[0] | is the source |
| sp[-1] | points to the target |
| sp[0] | is the second value |
| sp[-1] | is the first value |
| sp[0] | is the exit_code |
| sp[0] | is the value |
| sp[0] | is the expression to add |
| sp[0] | is the expression |
| sp[0] | is the expression |
| sp[0] | is the expression |
| sp[0] | is the expression |
| sp[0] | is the expression to use |
| sp[0] | holds a reference to the field to use |
| sp[0] | holds a reference to the field to use |
| cdp[0] | is a reference to the data to be split/assigned. |
| cdp[0] | holds a reference to $expression |
| cdp[1] | holds expression |
| sp[0] | holds a reference to the field to use |
| sp[0] | holds the field number |
| sp[0] | holds the field number |
| sp[0] | is the expression value |
| sp[0] | holds the second value. |
| sp[-1] | holds the first value. |
| sp[0] | holds the second value. |
| sp[-1] | holds the first value. |
| sp[0] | is the second string |
| sp[0] | is the first string |
| sp[0] | is the value |
| cdp[0] | holds the (signed) number of bytes by which to jump. |
| cdp[0] | holds the (signed) number of bytes by which to jump. |
| sp[0] | holds a value to compare against 0. |
| cdp[0] | holds the (signed) number of bytes by which to jump. |
| sp[0] | holds a value to compare against 0. |
| cdp[0] | holds the offset from the frame pointerfp. |
| cdp[0] | holds the offset from the frame pointerfp. |
| cdp[0] | holds the offset from the frame pointerfp of a reference to an array. |
| cdp[0] | holds the offset from the frame pointerfp of a reference to an array. |
| sp[0] | holds an expression |
| cdp[0] | holds the offset from the frame pointerfp of a reference to an array. |
| sp[0] | holds an expression |
| sp[0] | is the string or array reference |
| cdp[0] | holds the (signed) number of bytes by which to jump if the value is nonzero. |
| sp[0] | holds a value to compare against 0. |
| cdp[0] | holds the (signed) number of bytes by which to jump if the value is zero. |
| sp[0] | holds a value to compare against 0. |
| sp[0] | is the value |
| sp[0] | holds the second value. |
| sp[-1] | holds the first value. |
| sp[0] | holds the second value. |
| sp[-1] | holds the first value. |
| cdp[0] | holds a reference to a regular expression. |
| cdp[0] | holds a reference to a regular expression. |
| sp[0] | holds an expression to test. |
| sp[0] | holds a reference to a regular expression. |
| sp[-1] | holds an expression to test. |
| sp[0] | holds the date-specification string |
| sp[0] | holds the second operand |
| sp[-1] | holds the first operand |
| sp[0] | holds the second operand |
| cdp[0] | holds the first operand |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| sp[0] | is the second value |
| sp[-1] | is the first value |
| sp[0] | holds a value to negate. |
| sp[0] | holds the value to decrement |
| sp[0] | holds the value to increment |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| cdp[0] | is a reference to the variable which will be assigned the result |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| sp[0] | holds the value to decrement. |
| sp[0] | holds the value to decrement. |
| cdp[0] | array reference follows the command. |
| cdp[0] | is a reference to the data to push |
| cdp[0] | is a reference to the data to push |
| cdp[0] | is a reference to the data cell to copy. |
| cdp[0] | holds the type to set in the new slot, e.g., for data via I/O redirection |
| cdp[0] | holds a reference to the string value |
| cdp[0].op | a flag, test pat1 if on else pat2 |
| cdp[1].op | offset of pat2 code from cdp |
| cdp[2].op | offset of action code from cdp |
| cdp[3].op | offset of code after the action from cdp |
| cdp[4] | start of pat1 code |
| sp[0] | holds arguments for the action. |
| sp[0] | holds the return value |
| sp[0] | is modified to make the value uninitialized. |
| sp[0] | holds a reference to the array |
| sp[-1] | holds a reference to the iteration variable |
| sp[0] | holds the value |
| sp[0] | is the last parameter value; there can be up to 255. |
| sp[0] | is the value |
| sp[0] | is the seed value, which may be uninitialized |
| sp[0] | is the utc flag |
| sp[-1] | is the timestamp value |
| sp[-2] | is the format |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| cdp[0] | holds a reference to the variable to which to assign the result |
| sp[0] | holds the second value |
| sp[-1] | holds the first value |
| sp[0] | holds the length n. |
| sp[0] | holds the index i. |
| sp[0] | holds the string s. |
| sp[0] | is the command to execute |
| sp[0] | holds a value to test. |
| sp[0] | is the value to convert |
| sp[0] | is the value to convert |
| sp[0] | contains a value to negate. As a side-effect, if the value is a string, it is cast to double floating point. |
| sp[0] | contains a value to use. As a side-effect, if the value is a string, it is cast to double floating point. |
NAME
mawk-code - dumping mawk's byte-code
SYNOPSIS
At startup, mawk compiles the script into byte-code. After that, it interprets the compiled byte-code. Use the -Wdump option to show the byte-code.
PROGRAM CODES
As mawk executes the program, it maintains a reference to the command to execute in cdp. After that there may be data and/or references in cdp[0], cdp[1], etc.
When an operation requires operands, mawk pushes the values (or array/string references) onto the stack, which updates the stack pointer sp. When the operation completes, mawk consumes those entries on the stack, pushing the result (if any) onto the stack.
While executing user-defined functions, mawk maintains a frame pointerfp to address the function's local variables.
a_cat
Concatenate array-indices.
Usage:
Parameters:
- cdp[0]
cnt, the number of elements to concatenate follows the command.
- sp[0]..sp[1-cnt]
hold reference to the elements to concatenate.
a_del
Delete an array item.
Usage:
Parameters:
- sp[0]
points to array
- sp[-1]
is an expr
a_length
Find the length of an array.
Usage:
Parameters:
- sp[0]
points to array.
Returns the length of the array in sp[0].
a_pusha
Push array address onto stack.
Usage:
Parameters:
- cdp[0]
array reference follows the command.
Returns the array in sp[0].
a_test
Test if an expression is present in an array.
Usage:
Parameters:
- sp[0]
points to an array.
- sp[-1]
is an expression.
Returns 1 in sp[0] if the expression is found, 0 otherwise.
add
Add two numbers.
Usage:
Parameters:
- sp[0]
holds the second value.
- sp[-1]
holds the first value.
Returns the sum in sp[0].
add_asg
Combined addition/assignment.
Usage:
Parameters:
- sp[0]
is the source expression
- sp[-1]
points to the target
Stores the sum in the target, leaving sp[0] pointing to the target.
ae_pusha
Push reference to array cell, given expression for its index.
Usage:
Parameters:
- cdp[0]
an array reference follows the command.
- sp[0]
has an expression, used for the index of a cell in the array.
Returns a reference to the addressed cell in sp[0].
ae_pushi
Push contents of array cell, given expression for its index.
Usage:
Parameters:
- sp[0]
has an expression, used for the index of a cell in the array.
Returns contents of the addressed cell in sp[0].
aloop
Update reference to next cell for array loop.
Usage:
Parameters:
- none
Mawk maintains a stack of array-loop state. It updates the array/cell references in the current loop's state.
assign
Assigns a value.
Usage:
Parameters:
- sp[0]
is the source expression
- sp[-1]
points to the target
Stores the sum in the target, leaving sp[0] pointing to the target.
atan2
Compute arc-tangent of two values.
Usage:
Parameters:
- sp[0]
holds the second value
- sp[-1]
holds the first value
Returns the result in sp[0].
call
Call a function.
Usage:
Parameters:
- cdp[0]
is a reference to the function block
- cdp[1]
holds number of input arguments
Returns function value in sp[0].
cat
Concatenate two strings.
Usage:
Parameters:
- sp[0]
is the second string.
- sp[-1]
is the first string.
Returns the result in sp[0].
close
Close the file or pipe associated with an expression.
Usage:
Parameters:
- sp[0]
holds the expression identifying the file to close
Returns the status from closing the file, 0 on success or -1 on failure.
cos
Compute the cosine of a value in radians.
Usage:
Parameters:
- sp[0]
is the value.
Returns the result in sp[0].
del_a
Delete an array.
Usage:
Parameters:
- sp[0]
is the array to delete.
div
Divide one number by another.
Usage:
Parameters:
- sp[0]
is the second value.
- sp[-1]
is the first value.
Returns the quotient in sp[0].
div_asg
Combined division/assignment.
Usage:
Parameters:
- sp[0]
is the source
- sp[-1]
points to the target
Stores the quotient in the target, leaving sp[0] pointing to the target.
eq
Compare two values.
Usage:
Parameters:
- sp[0]
is the second value
- sp[-1]
is the first value
Returns 1 in sp[0] if the values are equal, otherwise 0.
exit
Exits mawk with a specific exit-code.
Usage:
Parameters:
- sp[0]
is the exit_code
exit0
Exits mawk with success
Usage:
Parameters:
exp
Compute base-e exponential function of a value.
Usage:
Parameters:
- sp[0]
is the value
Returns the result in sp[0].
f_add_asg
Combination addition/assignment to NF.
Usage:
Parameters:
- sp[0]
is the expression to add
f_assign
Assign an expression to NF.
Usage:
Parameters:
- sp[0]
is the expression
f_div_asg
Combination division/assignment to NF.
Usage:
Parameters:
- sp[0]
is the expression
f_mod_asg
Combination modulus/assignment to NF.
Usage:
Parameters:
- sp[0]
is the expression
f_mul_asg
Combination multiplication/assignment to NF.
Usage:
Parameters:
- sp[0]
is the expression
f_post_dec
Post-decrement using NF.
Usage:
Parameters:
f_post_inc
Post-increment using NF.
Usage:
Parameters:
f_pow_asg
Exponentiation using NF.
Usage:
Parameters:
- sp[0]
is the expression to use
f_pre_dec
Predecrement using NF.
Usage:
Parameters:
- sp[0]
holds a reference to the field to use
f_pre_inc
Preincrement using NF.
Usage:
Parameters:
- sp[0]
holds a reference to the field to use
f_pusha
Push array reference to data split-up as fields..
Usage:
Parameters:
- cdp[0]
is a reference to the data to be split/assigned.
Returns the resulting array reference in sp[0].
f_pushi
Push contents of numbered field.
Usage:
Parameters:
- cdp[0]
holds a reference to $expression
- cdp[1]
holds expression
Returns the field's value in sp[0].
f_sub_asg
Combination subtraction/assignment to NF.
Usage:
Parameters:
- sp[0]
holds a reference to the field to use
fe_pusha
Push reference to numbered field.
Usage:
Parameters:
- sp[0]
holds the field number
Returns a reference to the field in sp[0].
fe_pushi
Push content of numbered field.
Usage:
Parameters:
- sp[0]
holds the field number
Returns the field's content in sp[0].
fflush
Flush the output file or pipe associated with an expression.
Usage:
Parameters:
- sp[0]
is the expression value
Returns the result in sp[0].
gt
Test if first value is greater than the second.
Usage:
Parameters:
- sp[0]
holds the second value.
- sp[-1]
holds the first value.
Returns 1 in sp[0] if the first value is greater than, otherwise 0.
gte
Test if first value is greater than or equal to the second.
Usage:
Parameters:
- sp[0]
holds the second value.
- sp[-1]
holds the first value.
Returns 1 in sp[0] if the first value is greater than or equal, otherwise 0.
index
Find the position of the second string in the first.
Usage:
Parameters:
- sp[0]
is the second string
- sp[0]
is the first string
Returns the position in sp[0] starting at 1 if found, 0 if not found.
int
Returns a value truncated towards zero..
Usage:
Parameters:
- sp[0]
is the value
Returns the result in sp[0].
jmain
Go from BEGIN code to MAIN code.
Usage:
Parameters:
- none
jmp
Jump to a new byte-code position, by a given number of bytes.
Usage:
Parameters:
- cdp[0]
holds the (signed) number of bytes by which to jump.
jnz
Jump to a new byte-code position if sp[0] is nonzero,by a given number of bytes.
Usage:
Parameters:
- cdp[0]
holds the (signed) number of bytes by which to jump.
- sp[0]
holds a value to compare against 0.
jz
Jump to a new byte-code position if sp[0] is zero, by a given number of bytes.
Usage:
Parameters:
- cdp[0]
holds the (signed) number of bytes by which to jump.
- sp[0]
holds a value to compare against 0.
l_pusha
Push a local address onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds the offset from the frame pointerfp.
Returns the address in sp[0].
l_pushi
Push contents of a local variable onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds the offset from the frame pointerfp.
Returns the contents of the local variable in sp[0].
la_pusha
Pushes a reference to an array onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds the offset from the frame pointerfp of a reference to an array.
Returns a reference to the array in sp[0].
lae_pusha
Pushes a reference to a given array cell onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds the offset from the frame pointerfp of a reference to an array.
- sp[0]
holds an expression
Returns a reference to the specified array cell in sp[0].
lae_pushi
Pushes the contents of a given array cell onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds the offset from the frame pointerfp of a reference to an array.
- sp[0]
holds an expression
Returns the contents of the specified array cell in sp[0].
length
Returns the length of a string or array value.
Usage:
Parameters:
- sp[0]
is the string or array reference
Returns the length in sp[0].
ljnz
Special jump for logical-OR, always preceded bytest.
Usage:
Parameters:
- cdp[0]
holds the (signed) number of bytes by which to jump if the value is nonzero.
- sp[0]
holds a value to compare against 0.
ljz
Special jump for logical-OR, always preceded bytest.
Usage:
Parameters:
- cdp[0]
holds the (signed) number of bytes by which to jump if the value is zero.
- sp[0]
holds a value to compare against 0.
log
Compute the natural logarithm of a value.
Usage:
Parameters:
- sp[0]
is the value
Returns the result in sp[0].
lt
Test if first value is less than the second.
Usage:
Parameters:
- sp[0]
holds the second value.
- sp[-1]
holds the first value.
Returns 1 in sp[0] if the first value is less than, otherwise 0.
lte
Test if first value is less than or equal to the second.
Usage:
Parameters:
- sp[0]
holds the second value.
- sp[-1]
holds the first value.
Returns 1 in sp[0] if the first value is less than or equal, otherwise 0.
match0
Test if $0 matches a given regular expression.
Usage:
Parameters:
- cdp[0]
holds a reference to a regular expression.
Returns 1 in sp[0] if $0 matches the regular expression, 0 otherwise.
match1
Test if a given expression matches a given regular expression.
Usage:
Parameters:
- cdp[0]
holds a reference to a regular expression.
- sp[0]
holds an expression to test.
Returns 1 in sp[0] if the expression matches the regular expression, 0 otherwise.
match2
Test if an expression in sp[-1] matches the regular expression in sp[0].
Usage:
Parameters:
- sp[0]
holds a reference to a regular expression.
- sp[-1]
holds an expression to test.
Returns 1 in sp[0] if the expression matches the regular expression, 0 otherwise.
mktime
Converts a date specification in systime format to a timestamp.
Usage:
Parameters:
- sp[0]
holds the date-specification string
Returns the result in sp[0].
mod
Compute modulus/remainder with two operands.
Usage:
Parameters:
- sp[0]
holds the second operand
- sp[-1]
holds the first operand
Returns the remainder in sp[0].
mod_asg
Assign modulus/remainder with two operands.
Usage:
Parameters:
- sp[0]
holds the second operand
- cdp[0]
holds the first operand
Returns the remainder in sp[0] as well as replacing the first value.
mul
Compute product with two operands.
Usage:
Parameters:
- sp[0]
holds the second value
- sp[-1]
holds the first value
Returns the product in sp[0].
mul_asg
Assign product with two operands.
Usage:
Parameters:
- sp[0]
holds the second value
- sp[-1]
holds the first value
Returns the product in sp[0] as well as replacing the first value.
neq
Compare two values.
Usage:
Parameters:
- sp[0]
is the second value
- sp[-1]
is the first value
Returns 1 in sp[0] if the values are not equal, otherwise 0.
next
Read the next record, restart pattern testing.
Usage:
Parameters:
- none
nextfile
Begin processing the next file listed on the command line.
Usage:
Parameters:
- none
nf_pushi
Push the number of fields (NF) onto the evaluation stack.
Usage:
Parameters:
- none
not
Compute a logical negation.
Usage:
Parameters:
- sp[0]
holds a value to negate.
Returns the result on the evaluation stack, i.e., 0 if the value is nonzero and 1 otherwise.
ol_gl
Read into $0 using getline.
Usage:
Parameters:
- none
ol_gl_nr
Read into $0 using getline, updating NR and FNR.
Usage:
Parameters:
- none
omain
Start executing the main section of the script (between BEGIN and END).
Usage:
Parameters:
- none
pop
Pop the evaluation stack, discarding the value.
Usage:
Parameters:
- none
pop_al
Finish an array “in” loop, deallocating the state information.
Usage:
Parameters:
- none
post_dec
Post-decrement a value.
Usage:
Parameters:
- sp[0]
holds the value to decrement
Returns the updated value in sp[0].
post_inc
Post-increment a value.
Usage:
Parameters:
- sp[0]
holds the value to increment
Returns the updated value in sp[0].
pow
Compute the first value raised to the power of the second value.
Usage:
Parameters:
- sp[0]
holds the second value
- sp[-1]
holds the first value
Returns the result in sp[0].
pow_asg
Assign the first value raised to the power of the second value.
Usage:
Parameters:
- cdp[0]
is a reference to the variable which will be assigned the result
- sp[0]
holds the second value
- sp[-1]
holds the first value
pre_dec
Pre-decrement a value.
Usage:
Parameters:
- sp[0]
holds the value to decrement.
Returns the updated value in sp[0];.
pre_inc
Pre-increment a value.
Usage:
Parameters:
- sp[0]
holds the value to decrement.
Returns the updated value in sp[0];.
pusha
Push array address onto stack.
Usage:
Parameters:
- cdp[0]
array reference follows the command.
Returns the array in sp[0].
pushc
Push a data cell onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
is a reference to the data to push
Returns a reference to the result in sp[0].
pushd
Push a double floating value onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
is a reference to the data to push
Returns a reference to the result in sp[0].
pushi
Push contents of next referenced variable onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
is a reference to the data cell to copy.
Returns a reference to the result in sp[0].
pushint
Reserve the next slot on the evaluation stack, setting its type.
Usage:
Parameters:
- cdp[0]
holds the type to set in the new slot, e.g., for data via I/O redirection
Returns a reference to the result in sp[0].
pushs
Push a reference to a string value onto the evaluation stack.
Usage:
Parameters:
- cdp[0]
holds a reference to the string value
Returns a reference to the result in sp[0].
rand
Returns a random number between zero and one..
Usage:
Parameters:
- none
Returns the result in sp[0].
range
Test a range pattern: pat1, pat2 { action }.
Usage:
Parameters:
- cdp[0].op
a flag, test pat1 if on else pat2
- cdp[1].op
offset of pat2 code from cdp
- cdp[2].op
offset of action code from cdp
- cdp[3].op
offset of code after the action from cdp
- cdp[4]
start of pat1 code
- sp[0]
holds arguments for the action.
ret
Return a function value.
Usage:
Parameters:
- sp[0]
holds the return value
When calling a function, mawk saves the current stack, creating a new one. On return, mawk restores the previous stack and returns the function value in sp[0].
ret0
Return from a function without providing a return-value.
Usage:
Parameters:
- sp[0]
is modified to make the value uninitialized.
As in the ret operation, mawk restores the previous stack. After the return, sp[0] is an uninitialized value.
set_al
Begin an array “in” loop.
Usage:
Parameters:
- sp[0]
holds a reference to the array
- sp[-1]
holds a reference to the iteration variable
Mawk pushes a new entry onto the array loop stack, and updates cdp to point to the statement to execute.
sin
Compute the sine of a value in radians.
Usage:
Parameters:
- sp[0]
holds the value
Returns the result in sp[0].
sprintf
Returns a string constructed from expression-list according to format.
Usage:
Parameters:
- sp[0]
is the last parameter value; there can be up to 255.
sqrt
Returns the square root of a value.
Usage:
Parameters:
- sp[0]
is the value
Returns the result in sp[0].
srand
Seeds the random number generator.
Usage:
Parameters:
- sp[0]
is the seed value, which may be uninitialized
Returns the previous seed value in sp[0].
stop
Finish a range pattern.
Usage:
Parameters:
- none
strftime
Formats the given timestamp using the given format.
Usage:
Parameters:
Zero to three parameters may be on the stack. If all three are used, they are as follows:
- sp[0]
is the utc flag
- sp[-1]
is the timestamp value
- sp[-2]
is the format
Returns the result in sp[0].
sub
Subtract the second value from the first.
Usage:
Parameters:
- sp[0]
holds the second value
- sp[-1]
holds the first value
Returns the result in sp[0].
sub_asg
Assign the difference of two values to a variable.
Usage:
Parameters:
- cdp[0]
holds a reference to the variable to which to assign the result
- sp[0]
holds the second value
- sp[-1]
holds the first value
Stores the difference in the target, leaving sp[0] pointing to the target.
substr
eturns the substring of string s, starting at index i, of length n.
Usage:
Parameters:
Two or three parameters may be on the stack. If all three are used, they are as follows:
- sp[0]
holds the length n.
- sp[0]
holds the index i.
- sp[0]
holds the string s.
system
Executes a command, returning the wait-status.
Usage:
Parameters:
- sp[0]
is the command to execute
Returns the wait-status in sp[0].
systime
Returns the current time of day as the number of seconds since the Epoch.
Usage:
Parameters:
- none
Returns the result in sp[0].
test
Test a logical expression.
Usage:
Parameters:
- sp[0]
holds a value to test.
Returns the result on the evaluation stack, i.e., 1 if the value is nonzero and 0 otherwise.
tolower
Copy a string, converting to lowercase.
Usage:
Parameters:
- sp[0]
is the value to convert
Returns the result in sp[0].
toupper
Copy a string, converting to uppercase.
Usage:
Parameters:
- sp[0]
is the value to convert
Returns the result in sp[0].
uminus
Unitary minus.
Usage:
Parameters:
- sp[0]
contains a value to negate. As a side-effect, if the value is a string, it is cast to double floating point.
Returns the result in sp[0].
uplus
Unitary plus.
Usage:
Parameters:
- sp[0]
contains a value to use. As a side-effect, if the value is a string, it is cast to double floating point.
Returns the result in sp[0].
REGULAR EXPRESSIONS
M_1J
mandatory jump
M_2JA
optional (undesirable) jump
M_2JB
optional (desirable) jump
M_2JC
pop position, optional jump (to continue looping) if advanced
M_ACCEPT
end of match
M_ANY
arbitrary character (.)
M_CLASS
character class
M_END
end of string ($)
M_ENTER
prepare an iteration by resetting the counter. This precedes a M_SAVE_POS.
M_LOOP
Like M_2JC, this is the last part of a conditional loop. It is used where one or both of the minimum and maximum iterations are known.
M_SAVE_POS
push position onto stack, at the beginning of a loop
M_START
start of string (^)
M_STR
matching a literal string
M_U
arbitrary string (.*)