DSL reference: syntax¶
Expression formatting¶
Multiple expressions may be given, separated by semicolons, and each may refer to the ones before:
ruby -e '10.times{|i|puts "i=#{i}"}' | mlr --opprint put '$j = $i + 1; $k = $i +$j'
i j k
0 1 1
1 2 3
2 3 5
3 4 7
4 5 9
5 6 11
6 7 13
7 8 15
8 9 17
9 10 19
Newlines within the expression are ignored, which can help increase legibility of complex expressions:
mlr --opprint put '
$nf = NF;
$nr = NR;
$fnr = FNR;
$filenum = FILENUM;
$filename = FILENAME
' data/small data/small2
a b i x y nf nr fnr filenum filename
pan pan 1 0.3467901443380824 0.7268028627434533 5 1 1 1 data/small
eks pan 2 0.7586799647899636 0.5221511083334797 5 2 2 1 data/small
wye wye 3 0.20460330576630303 0.33831852551664776 5 3 3 1 data/small
eks wye 4 0.38139939387114097 0.13418874328430463 5 4 4 1 data/small
wye pan 5 0.5732889198020006 0.8636244699032729 5 5 5 1 data/small
pan eks 9999 0.267481232652199086 0.557077185510228001 5 6 1 2 data/small2
wye eks 10000 0.734806020620654365 0.884788571337605134 5 7 2 2 data/small2
pan wye 10001 0.870530722602517626 0.009854780514656930 5 8 3 2 data/small2
hat wye 10002 0.321507044286237609 0.568893318795083758 5 9 4 2 data/small2
pan zee 10003 0.272054845593895200 0.425789896597056627 5 10 5 2 data/small2
mlr --opprint filter '($x > 0.5 && $y < 0.5) || ($x < 0.5 && $y > 0.5)' \
then stats2 -a corr -f x,y \
data/medium
x_y_corr
-0.7479940285189345
Expressions from files¶
The simplest way to enter expressions for put and filter is between single quotes on the command line, e.g.
mlr --from data/small put '$xy = sqrt($x**2 + $y**2)'
a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,xy=0.8052985815845617
a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,xy=0.9209978658539777
a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,xy=0.3953756915115773
a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,xy=0.40431685157744135
a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729,xy=1.036584492737304
mlr --from data/small put 'func f(a, b) { return sqrt(a**2 + b**2) } $xy = f($x, $y)'
a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,xy=0.8052985815845617
a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,xy=0.9209978658539777
a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,xy=0.3953756915115773
a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,xy=0.40431685157744135
a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729,xy=1.036584492737304
You may, though, find it convenient to put expressions into files for reuse, and read them using the -f option. For example:
cat data/fe-example-3.mlr
func f(a, b) {
return sqrt(a**2 + b**2)
}
$xy = f($x, $y)
mlr --from data/small put -f data/fe-example-3.mlr
a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,xy=0.8052985815845617
a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,xy=0.9209978658539777
a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,xy=0.3953756915115773
a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,xy=0.40431685157744135
a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729,xy=1.036584492737304
If you have some of the logic in a file and you want to write the rest on the command line, you can use the -f and -e options together:
cat data/fe-example-4.mlr
func f(a, b) {
return sqrt(a**2 + b**2)
}
mlr --from data/small put -f data/fe-example-4.mlr -e '$xy = f($x, $y)'
a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,xy=0.8052985815845617
a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,xy=0.9209978658539777
a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,xy=0.3953756915115773
a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,xy=0.40431685157744135
a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729,xy=1.036584492737304
A suggested use-case here is defining functions in files, and calling them from command-line expressions.
Another suggested use-case is putting default parameter values in files, e.g. using begin{@count=is_present(@count)?@count:10} in the file, where you can precede that using begin{@count=40} using -e.
Moreover, you can have one or more -f expressions (maybe one function per file, for example) and one or more -e expressions on the command line. If you mix -f and -e then the expressions are evaluated in the order encountered. (Since the expressions are all simply concatenated together in order, don’t forget intervening semicolons: e.g. not mlr put -e '$x=1' -e '$y=2 ...' but rather mlr put -e '$x=1;' -e '$y=2' ....)
Semicolons, commas, newlines, and curly braces¶
Miller uses semicolons as statement separators, not statement terminators. This means you can write:
mlr put 'x=1'
mlr put 'x=1;$y=2'
mlr put 'x=1;$y=2;'
mlr put 'x=1;;;;$y=2;'
Semicolons are optional after closing curly braces (which close conditionals and loops as discussed below).
echo x=1,y=2 | mlr put 'while (NF < 10) { $[NF+1] = ""} $foo = "bar"'
x=1,y=2,3=,4=,5=,6=,7=,8=,9=,10=,foo=bar
echo x=1,y=2 | mlr put 'while (NF < 10) { $[NF+1] = ""}; $foo = "bar"'
x=1,y=2,3=,4=,5=,6=,7=,8=,9=,10=,foo=bar
Semicolons are required between statements even if those statements are on separate lines. Newlines are for your convenience but have no syntactic meaning: line endings do not terminate statements. For example, adjacent assignment statements must be separated by semicolons even if those statements are on separate lines:
mlr put '
$x = 1
$y = 2 # Syntax error
'
mlr put '
$x = 1;
$y = 2 # This is OK
'
Trailing commas are allowed in function/subroutine definitions, function/subroutine callsites, and map literals. This is intended for (although not restricted to) the multi-line case:
mlr --csvlite --from data/a.csv put '
func f(
num a,
num b,
): num {
return a**2 + b**2;
}
$* = {
"s": $a + $b,
"t": $a - $b,
"u": f(
$a,
$b,
),
"v": NR,
}
'
s,t,u,v
3,-1,5,1
9,-1,41,2
Bodies for all compound statements must be enclosed in curly braces, even if the body is a single statement:
mlr put 'if ($x == 1) $y = 2' # Syntax error
mlr put 'if ($x == 1) { $y = 2 }' # This is OK
Bodies for compound statements may be empty:
mlr put 'if ($x == 1) { }' # This no-op is syntactically acceptable