switch

Operator

  switch — route values based on cases

Synopsis

switch <expr> (
  case <const> => <branch>
  case <const> => <branch>
  ...
  [ default => <branch> ]
)

switch (
  case <bool-expr> => <branch>
  case <bool-expr> => <branch>
  ...
  [ default => <branch> ]
)

Description

The switch operator routes input values to multiple, parallel branches of the pipeline based on case matching.

In this first form, the expression <expr> is evaluated for each input value and its result is compared with all of the case values, which must be distinct, compile-time constant expressions. The value is propagated to the matching branch.

In the second form, each case is evaluated for each input value in the order that the cases appear. The first case to match causes the input value to propagate to the corresponding branch. Even if later cases match, only the first branch receives the value.

In either form, if no case matches, but a default is present, then the value is routed to the default branch. Otherwise, the value is dropped.

Only one default case is allowed and it may appear anywhere in the list of cases; where it appears does not influence the result.

The output of a switch consists of multiple branches that must be merged. If the downstream operator expects a single input, then the output branches are merged with an automatically inserted combine operator.

Examples

Split input into evens and odds

echo '1 2 3 4' |
  zq -z '
    switch (
      case this%2==0 => {even:this}
      case this%2==1 => {odd:this}
    )
    | sort odd,even
  ' -

=>

{odd:1}
{odd:3}
{even:2}
{even:4}

Switch on this with a constant case

echo '1 2 3 4' |
  zq -z '
    switch this (
      case 1 => yield "1!"
      default => yield string(this)
    )
    | sort
  ' -

=>

"1!"
"2"
"3"
"4"