tcltclsh

How to limit standard output at tclsh command line?

When running commands interactively at the tclsh command line, is there a way to truncate how much of a return value gets printed to stdout?

For example, this will take a very long time because the return value will print to stdout.

tclsh> set a [lrepeat 500000000 x]

I know I can add a dummy command in the same line, but this is an ad hoc solution. Is there some I could set in my ~/.tclshrc to truncate stdout to a finite length?

tclsh> set a [lrepeat 500000000 x] ; puts ""
Solution

  • Maybe this is an XY-problem (as turning off or swallowing prints to stdout seems to satisfy the OP), but the actual question was:

    Is there some I could set in my ~/.tclshrc to truncate stdout to a finite length?

    You can use an interceptor on stdout (and/ or, stderr) to cap strings to a default limit:

    oo::class create capped {
  variable max
  constructor {m} {
    set max $m
  } 
  method initialize {handle mode} {
    if {$mode ne "write"} {error "can't handle reading"}
    return {finalize initialize write}
  }
  method finalize {handle} {
    # NOOP
  }
  
  method write {handle bytes} {
    if {[string length $bytes] > $max} {
      set enc [encoding system]
      set str [encoding convertfrom $enc $bytes]
      set newStr [string range $str 0 $max-1]
      if {[string index $str end] eq "\n"} {
        append newStr "\n"
      }
      set bytes [encoding convertto $enc $newStr]
    }
    return $bytes
  }
}

    Using chan push and chan pop you may turn on/off capping to, e.g., 30 characters:

    % chan push stdout [capped new 30]
serial1
% puts [string repeat € 35]
€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€
% chan pop stdout
% puts [string repeat € 35]
€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€

    Some remarks: