Content-type: text/html Man page of Term::ReadLine


Section: Perl Programmers Reference Guide (3perl)
Updated: 2007-12-18
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Term::ReadLine - Perl interface to various "readline" packages. If no real package is found, substitutes stubs instead of basic functions.  


  use Term::ReadLine;
  my $term = new Term::ReadLine 'Simple Perl calc';
  my $prompt = "Enter your arithmetic expression: ";
  my $OUT = $term->OUT || \*STDOUT;
  while ( defined ($_ = $term->readline($prompt)) ) {
    my $res = eval($_);
    warn $@ if $@;
    print $OUT $res, "\n" unless $@;
    $term->addhistory($_) if /\S/;



This package is just a front end to some other packages. It's a stub to set up a common interface to the various ReadLine implementations found on CPAN (under the "Term::ReadLine::*" namespace).  

Minimal set of supported functions

All the supported functions should be called as methods, i.e., either as

  $term = new Term::ReadLine 'name';

or as


where $term is a return value of Term::ReadLine->new().

returns the actual package that executes the commands. Among possible values are "Term::ReadLine::Gnu", "Term::ReadLine::Perl", "Term::ReadLine::Stub".
returns the handle for subsequent calls to following functions. Argument is the name of the application. Optionally can be followed by two arguments for "IN" and "OUT" filehandles. These arguments should be globs.
gets an input line, possibly with actual "readline" support. Trailing newline is removed. Returns "undef" on "EOF".
adds the line to the history of input, from where it can be used if the actual "readline" is present.
"IN", "OUT"
return the filehandles for input and output or "undef" if "readline" input and output cannot be used for Perl.
If argument is specified, it is an advice on minimal size of line to be included into history. "undef" means do not include anything into history. Returns the old value.
returns an array with two strings that give most appropriate names for files for input and output using conventions "<$in", ">out".
returns a reference to a hash which describes internal configuration of the package. Names of keys in this hash conform to standard conventions with the leading "rl_" stripped.
Returns a reference to a hash with keys being features present in current implementation. Several optional features are used in the minimal interface: "appname" should be present if the first argument to "new" is recognized, and "minline" should be present if "MinLine" method is not dummy. "autohistory" should be present if lines are put into history automatically (maybe subject to "MinLine"), and "addhistory" if "addhistory" method is not dummy.

If "Features" method reports a feature "attribs" as present, the method "Attribs" is not dummy.


Additional supported functions

Actually "Term::ReadLine" can use some other package, that will support a richer set of commands.

All these commands are callable via method interface and have names which conform to standard conventions with the leading "rl_" stripped.

The stub package included with the perl distribution allows some additional methods:

makes Tk event loop run when waiting for user input (i.e., during "readline" method).
makes the command line stand out by using termcap data. The argument to "ornaments" should be 0, 1, or a string of a form "aa,bb,cc,dd". Four components of this string should be names of terminal capacities, first two will be issued to make the prompt standout, last two to make the input line standout.
takes two arguments which are input filehandle and output filehandle. Switches to use these filehandles.

One can check whether the currently loaded ReadLine package supports these methods by checking for corresponding "Features".  




The environment variable "PERL_RL" governs which ReadLine clone is loaded. If the value is false, a dummy interface is used. If the value is true, it should be tail of the name of the package to use, such as "Perl" or "Gnu".

As a special case, if the value of this variable is space-separated, the tail might be used to disable the ornaments by setting the tail to be "o=0" or "ornaments=0". The head should be as described above, say

If the variable is not set, or if the head of space-separated list is empty, the best available package is loaded.

  export "PERL_RL=Perl o=0"     # Use Perl ReadLine without ornaments
  export "PERL_RL= o=0"         # Use best available ReadLine without ornaments

(Note that processing of "PERL_RL" for ornaments is in the discretion of the particular used "Term::ReadLine::*" package).  


It seems that using Term::ReadLine from Emacs minibuffer doesn't work quite right and one will get an error message like

    Cannot open /dev/tty for read at ...

One possible workaround for this is to explicitly open /dev/tty like this

    open (FH, "/dev/tty" )
      or eval 'sub Term::ReadLine::findConsole { ("&STDIN", "&STDERR") }';
    die $@ if $@;
    close (FH);

or you can try using the 4-argument form of Term::ReadLine->new().



Minimal set of supported functions
Additional supported functions

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Time: 04:14:18 GMT, September 24, 2010