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ARB Command Interpreter (ACI)



[ export db ]

[ ARB_NT/Species/search/parse_fields ]



ACI is a simple command interpreter, which uses streams of data as central concept.

Many ACI commands have parameters which are specified behind the command in parenthesis.

All ACI commands

  • take the data from (one or multiple) input streams,
  • modify that data and
  • write that data to (one or multiple) output streams.
    e.g. the command 'count("a")' counts every 'a' for each input stream and generates one output stream (containing the char count) for every input stream.

The first input stream always is a single stream, often the value of a database field (e.g. when ACI is used in ´Node Display Setup (NDS)´).

The number of output streams depends on the used command:

  • most commands produce one output stream for each input stream (as the count-example above)
  • some commands combine two input streams into one output stream (e.g. see binary operators below)
  • some commands ignore all input streams and create one output streams (e.g. 'readdb(fieldname)')
  • Note: special stream related commands are documented in section 'STREAM HANDLING'

Multiple commands can be separated by two operator symbols: ';' and '|'.

  • ';' binds stronger than '|'
  • commands separated by ';' form a command-list and operate independently from each other:
    • all(!) commands use all(!) input streams
    • each command generates its own output streams

  • the '|' operator acts as processing sequence point, i.e.
    • all output streams generated by the command-list on the left side of the '|' will be passed
    • as input streams to the command-list on the right side of the '|'.

Finally (at the end of the overall ACI expression) all generated output streams get concatenated.

Typical uses are to

Instead of using ACI commands (as described in this document) you may always use any of the other integrated data processing languages. Simply prefix the command

Both are as well available inside ACI via the commands 'srt' and 'command', see below.




creates two streams:
  1. how many A's
  2. and how many A's and G's


per_cent is a command that divides two numbers (number of 'A's / number of 'G's) and returns the result as percent.

Example data flow

eg: count("A");count("G")|"a/g = "; per_cent

input                                                         concatenate output
"AGG" ----> count("A") -->| -----> "a/g = " --> | --> "a/g = " ---> 'a/g = 50'
      \                   | \ /                 |               /
       \                  |  \                  |              /
        \                 | / \                 |             /
         -> count("G") -->| -----> per_cent --> | --> "50" ---


Several commands expect or accept additional parameters in parenthesis (e.g. 'remove(aA)').

Multiple parameters have to be separated by ',' or ';'.

There are two distinct ways to specify such a parameter:

  • unquoted
    Unquoted parameters are taken as specified, despite the following exceptions:
    • ',;"|\)' need to be escaped by prefixing one '\'
    • spaces will get removed if unprefixed by '\'

  • quoted
    Quoted parameters begin and end with a '"'. You can use any character, but you need to escape '\' and '"' by preceeding a '\'.
    Example: 'remove("\"")' will remove all double quotes from input.
             'remove("\\")' will remove all backslashes from input.

[@@@ behavior currently not strictly implemented]



If not explicitely mentioned, every command creates one output stream for each input stream.


echo(x1;x2;x3...)       creates one output stream from each specified parameter
                        (parameters are separated by ';').
"text"                  same as 'echo("text")'
dd                      copies all input streams to output streams
cut(N1,N2,N3)           copies the Nth input stream(s)
drop(N1,N2)             copies all but the Nth input stream(s)
dropempty               drops all empty input streams
dropzero                drops all non-numeric or zero input streams
swap(N1,N2)             swaps two input streams
                        (w/o parameters: swaps last two streams)
toback(X)               moves the Xth input stream
                        to the end of output streams
tofront(X)              moves the Xth input stream
                        to the start of output streams
merge([sep])            merges all input streams into one output stream.
                        If 'sep' is specified, it's inserted between them.
                        If no input streams are given, it returns 1 empty
                        input stream.
split([sep[,mode]])     splits all input streams at separator string 'sep'
                        (default: split at linefeed).
0               remove found separators (default)
1               split before separator
2               split after separator
streams                 returns the number of input streams


head(n)                 the first n characters
left(n)                 the first n characters
tail(n)                 the last n characters
right(n)                the last n characters
the above functions return an empty string for n<=0
len                     the length of the input
len("chr")              the length of the input excluding the
                        characters in 'chr'
mid(x,y)                the substring string from position x to y
Allowed positions are
  • [1..N] for mid()
  • [0..N-1] for mid0()

A position below that range is relative to the end of the string, i.e. mid(-2,0) and mid0(-3,-1) are equiv to tail(3)
crop("str")             removes characters of 'str' from
                        both ends of the input
remove("str")           removes all characters of 'str'
                        e.g. remove(" ") removes all blanks
keep("str")             the opposite of remove:
                        remove all chars that are not a member
                        of 'str'
isEmpty                 return '1' for each empty input stream, '0' for others
srt("orig=dest",...)    replace command, invokes SRT
                        (see ´Search and Replace Tool (SRT)´)
translates all characters from input that occur in the first argument ("old") by the corresponding character of the second argument ("new").
An optional third argument (one character only) means: replace all other characters with the third argument.
Input:                        "--AabBCcxXy--"
translate("abc-","xyz-")      "--AxyBCzxXy--"
translate("abc-","xyz-",".")  "--.xy..z...--"
This can be used to replace illegal characters from sequence date (see predefined expressions in 'Modify fields of listed species').
tab(n)                  append n-len(input) spaces
pretab(n)               prepend n-len(input) spaces
upper                   converts string to upper case
lower                   converts string to lower case
caps                    capitalizes string
takes a long string and breaks it into several lines
option       (default)     description
width=#      (50)          line width
firsttab=#   (10)          first line left indent
tab=#        (10)          left indent (not first line)
"nl=chrs"    (" ")         list of characters that specify
                           a possibly point of a line break;
                           the line break characters get removed!
"forcenl=chrs" ("\n")      Force a newline at these characters.
(see also format_sequence below)
Search for all words (separated by ',' ';' ':' ' ' or 'tab') that contain more characters of type chars than val, sort them alphabetically and write them separated by ' ' to the output


escape         escapes all occurrences of '\' and '"' by preceeding a '\'
quote          quotes the input in '"'
unescape       inverse of escape
unquote        removes quotes (if present). otherwise return input


compare(a,b)             return -1 if a<b, 0 if a=b, 1 if a>b
equals(a,b)              return 1 if a=b, 0 otherwise
contains(a,b)            if a contains b, this returns the position of
                         b inside a (1..N) and 0 otherwise.
                         Always returns 0 if b is empty.
partof(a,b)              if a is part of b, this returns the position of
                         a inside b (1..N) and 0 otherwise.
The above functions are binary operators (see below). For each of them a case-insensitive alternative exists (icompare, iequals, ...).


All functions here operate with floating-point numbers.
isBelow(a,b)            return 1 if a<b, 0 otherwise
isAbove(a,b)            return 1 if a>b, 0 otherwise
isEqual(a,b)            return 1 if a=b, 0 otherwise
The above functions are binary operators (see below).
for values of each input stream: return 1 if low <= value <= high, 0 otherwise


plus                    add arguments
minus                   subtract arguments
mult                    multiply arguments
div                     divide arguments
per_cent                divide arguments * 100 (not rounded; use "fper_cent|round(0)")
rest                    divide arguments, take rest
Calculation is performed with integer numbers. For most of these functions a floating-point variant exists:
  • fplus
  • fminus
  • fmult
  • fdiv
  • fper_cent

rounds a floating-point input to the given numbers of digits behind the floating-point. Specify zero to round to an integer number. Specify negative digits to round to multiples of 10, 100, 1000, ...
To avoid 'division by zero'-errors, the operators 'div', 'per_cent' and 'rest' return 0 if the second argument is zero.
The above functions work as binary operators (see below).


All input streams are converted to boolean values (i.e. 0 or 1) as follows:
"0"         -> 0
any number  -> 1
any text    -> 0 (even empty text!)
Not     invert values of all input streams (0<->1)
And     return 1 if all input streams are 1, 0 otherwise
Or      return 1 if one input streams is  1, 0 otherwise
Use "|or|not" or "|and|not" to execute NOR or NAND.


Several operators work as so called 'binary operators'. These operators may be used in various ways, which are shown using the operator 'plus':
ACI                OUTPUT                  STREAMS
plus(a,b)          a+b                     input:0 output:1
a;b|plus           a+b                     input:2 output:1
a;b;c;d|plus       a+b;c+d                 input:4 output:2
a;b;c|operator(x)  a+x;b+x;c+x             input:3 output:3
That means, if the binary operator
  • has no arguments, it expects an even number of input streams. The operator is applied to the first 2 streams, then to the second 2 stream and so on. The number of output streams is half the number of input streams.
  • has 1 argument, it accepts one to many input streams. The operator is applied to each input stream together with the argument. For each input stream one output stream is generated.
  • has 2 arguments, it is applied to these. The arguments are interpreted as ACI commands and are applied for each input stream. The results of the commands are passed as arguments to the binary operator. For each input stream one output stream is generated.


select(a,b,c,...)       each input stream is converted into a number
                        (non-numeric text converts to zero). That number is
                        used to select one of the given arguments:
                             0 selects 'a',
                             1 selects 'b',
                             2 selects 'c' and so on.
                        The selected argument is interpreted as ACI command
                        and is applied to an empty input stream.


trace(onoff)            toggle tracing of ACI actions to standard output.
                        Parameter: 0 or 1 (switch off or on)
All streams are copied (like 'dd').
Example: "cmd1 | cmd2 | trace(1) | tracedCmd1 | tracedCmd2 | trace(0) | untracedCmd "
To see the output from trace, either


readdb(field_name)      the contents of the field 'field_name'
sequence                the sequence in the current alignment.
Note: older ARB versions returned 'no sequence' if the current alignment contained no sequence. Now it returns an empty string.
For genes it returns only the corresponding part of the sequence. If the field complement = 1 then the result is the reverse-complement.
sequence_type           the sequence type of the selected alignment ('rna','dna',..)
ali_name                the name of the selected alignment (e.g. 'ali_16s')
Note: The commands above only work at the beginning of the ACI expression.
checksum(options)       calculates a CRC checksum
                        "exclude=chrs"    remove 'chrs' before calculation
                        "toupper"         make everything uppercase first
gcgchecksum             a gcg compatible checksum
takes a long string ( sequence ) and breaks it into several lines
option       (default)  description
width=#      (50)       sequence line width
firsttab=#   (10)       first line left indent
tab=#        (10)       left indent (not first line)
numleft      (NO)       numbers on the left side
numright=#   (NO)       numbers on the right side (#=width)
gap=#        (10)       insert a gap every # seq. characters.
(see also 'format' above)
like extract_words, but do not sort words, but rel_len is the minimum percentage of characters of a word that mach a character in 'chars' before word is taken. All words will be separated by white space.
taxonomy([treename,] depth)
Returns the taxonomy of the current species or group as defined by a tree.
If 'treename' is specified, its used as tree, otherwise the 'default tree' is used (which in most cases is the tree displayed in the ARB_NT main window).
'depth' specifies how many "levels" of the taxonomy are used.


There are several functions to filter sequential data:
  • filter
  • diff
  • gc

All these functions use the following COMMON OPTIONS to define what is used as filter sequence:
  • species=name
    Use species 'name' as filter.
  • SAI=name
    Use SAI 'name' as filter.
  • first=1
    Use 1st input stream as filter for all other input streams.
  • pairwise=1
    Use 1st input stream as filter for 2nd stream, 3rd stream as filter for 4th stream, and so on.
  • align=ali_name
    Use alignment 'ali_name' instead of current default alignment (only meaningful together with 'species' or 'SAI').

Note: Only one of the parameters 'species', 'SAI', 'first' or 'pairwise' may be used.
Calculates the difference between the filter (see common options above) and the input stream(s) and write the result to output stream(s).
Additional options:
  • equal=x
    Character written to output if filter and stream are equal at a position (defaults to '.'). To copy the stream contents for equal columns, specify 'equal=' (directly followed by ',' or ')')
  • differ=y
    Character written to output if filter and stream don't match at one column position. Default is to copy the character from the stream.

Filters only specified columns out of the input stream(s). You need to specify either
  • exclude=xyz
    to use all columns, where the filter (see common options above) has none of the characters 'xyz'
  • include=xyz
    to use only columns, where the filter has one of the characters 'xyz'

All used columns are concatenated and written to the output stream(s).
Randomly modifies the content of columns selected by the filter (see common options above). Only columns containing letters will be modified.
The options 'include=xyz' and 'exclude=xyz' work like with 'filter()', but here they select the columns to modify - all other columns get copied unmodified.
How the selected columns are modified, is specified by the following parameters:
  • change=percent
    percentage of changed columns (default: silently change nothing, to make it more difficult for you to ignore this helpfile)
  • to=xy
    randomly change to one of the characters 'xy'.
    • Use 'xyy' to produce 33% 'x' and 66% 'y'
    • Use 'xxxxxxxxxy' to produce 90% 'x' and 10% 'y'
    • Use 'x' to replace all matching columns by 'x'

I think the intention for this (long undocumented) command is to easily generate artificial sequences with different GC-content, in order to test treeing-software.


Execute external (unix) command.
Given params will be single-quoted and passed to the command.
All input streams will be concatenated and piped into the command.
When the command itself is a pipe, put it in parenthesis (e.g. "(sort|uniq)"). Note: This won't work together with params.
The result is the output of the command.
You better not use this command for NDS, because any slow command will disable all editing -> You never can remove this command from the NDS. Even arb_panic will not easily help you.
applies 'action' to all input streams using
If you nest calls (i.e. if 'action' contains further calls to 'command') you have to apply escaping multiple times (e.g. inside an export filter - which is in fact an SRT expression - you'll have to use double escapes).
the 'exprEvalToAction' is evaluated (using an empty string as input) and the result is interpreted as action and gets applied to all input streams (as in 'command' above).
Example: Said you have two numeric positions stored in database fields
         'pos1' and 'pos2' for each species. Then the following command
         extracts the sequence data from pos1 to pos2:
'sequence|eval(" \"mid(\";readdb(pos1);\";\";readdb(pos2);\")\" ")'
How the example works:
The argument is the escaped version of the command '"mid(" ; readdb(pos1) ; ";" ; readdb(pos2) ; ")"'.
If pos1 contains '10' and pos2 contains '20' that command will evaluate to 'mid(10;20)'.
For these positions the executed ACI behaves like 'sequence|mid(10;20)'.
defines a ACI-macro 'name'. 'escapedCommand' contains an escaped ACI command sequence. This command sequence can be executed with do(name).
applies a previously defined ACI-macro to all input streams (see 'define').
'define(a,action)' followed by 'do(a)' works similar to 'command(action)'.
See embl.eft for an example using define and 'do'
origin_organism(action) origin_gene(action)
like command() but readdb() etc. reads all data from the origin organism/gene of a gene-species (not from the gene-species itself).
This function applies only to gene-species!

Future features


creates a character statistic of the sequence (not implemented yet)



fetches the default sequence, formats it, and prepends 'SEQUENCE_'.


get the default sequence, remove all '.-' and format it


the number of non '.-' symbols (sequence length )

"[";taxonomy(tree_other,3);" -> ";taxonomy(3);"]"

shows for each species how their taxonomy changed between "tree_other" and current tree

equals(readdb(tmp),readdb(acc))|select(echo("tmp and acc differ"),)

returns 'tmp and acc differ' if the content of the database fields 'tmp' and 'acc' differs. empty result otherwise.


returns the content of the 'full_name' database entry if it contains the substring 'bacillus'. Otherwise returns '..'


The output of taxonomy() is not always instantly refreshed.