Tim Maher > Shell-POSIX-Select-0.05 > Shell::POSIX::Select

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NAME ^

Shell::POSIX::Select - The POSIX Shell's "select" loop for Perl

PURPOSE ^

This module implements the select loop of the "POSIX" shells (Bash, Korn, and derivatives) for Perl. That loop is unique in two ways: it's by far the friendliest feature of any UNIX shell, and it's the only UNIX shell loop that's missing from the Perl language. Until now!

What's so great about this loop? It automates the generation of a numbered menu of choices, prompts for a choice, proofreads that choice and complains if it's invalid (at least in this enhanced implementation), and executes a code-block with a variable set to the chosen value. That saves a lot of coding for interactive programs -- especially if the menu consists of many values!

The benefit of bringing this loop to Perl is that it obviates the need for future programmers to reinvent the Choose-From-A-Menu wheel.

SYNOPSIS ^

select [ [my|local|our] scalar_var ] ( [LIST] ) { [CODE] }

In the above, the enclosing square brackets (not typed) identify optional elements, and vertical bars separate mutually-exclusive choices:

The required elements are the keyword select, the parentheses, and the curly braces. See "SYNTAX" for details.

ELEMENTARY EXAMPLES ^

NOTE: All non-trivial programming examples shown in this document are distributed with this module, in the Scripts directory. "ADDITIONAL EXAMPLES", covering more features, are shown below.

ship2me.plx

    use Shell::POSIX::Select;

    select $shipper ( 'UPS', 'FedEx' ) {
        print "\nYou chose: $shipper\n";
        last;
    }
    ship ($shipper, $ARGV[0]);  # prints confirmation message

Screen

    ship2me.plx  '42 hemp toothbrushes'  # program invocation
    
    1) UPS   2) FedEx
    
    Enter number of choice: 2
    
    You chose: FedEx
    Your order has been processed.  Thanks for your business!

ship2me2.plx

This variation on the preceding example shows how to use a custom menu-heading and interactive prompt.

    use Shell::POSIX::Select qw($Heading $Prompt);

    $Heading='Select a Shipper' ;
    $Prompt='Enter Vendor Number: ' ;

    select $shipper ( 'UPS', 'FedEx' ) {
      print "\nYou chose: $shipper\n";
      last;
    }
    ship ($shipper, $ARGV[0]);  # prints confirmation message

Screen

    ship2me2.plx '42 hemp toothbrushes'

    Select a Shipper

    1) UPS   2) FedEx

    Enter Vendor Number: 2

    You chose: FedEx
    Your order has been processed.  Thanks for your business!

SYNTAX ^

Loop Structure

Supported invocation formats include the following:

 use Shell::POSIX::Select ;

 select                 ()      { }         # Form 0
 select                 ()      { CODE }    # Form 1
 select                 (LIST)  { CODE }    # Form 2
 select         $var    (LIST)  { CODE }    # Form 3
 select my      $var    (LIST)  { CODE }    # Form 4
 select our     $var    (LIST)  { CODE }    # Form 5
 select local   $var    (LIST)  { CODE }    # Form 6

If the loop variable is omitted (as in Forms 0, 1 and 2 above), it defaults to $_, localized to the loop's scope. If the LIST is omitted (as in Forms 0 and 1), @ARGV is used by default, unless the loop occurs within a subroutine, in which case @_ is used instead. If CODE is omitted (as in Form 0, it defaults to a statement that prints the loop variable.

The cases shown above are merely examples; all reasonable permutations are permitted, including:

 select       $var    (    )  { CODE }        
 select local $var    (LIST)  {      }

The only form that's not allowed is one that specifies the loop-variable's declarator without naming the loop variable, as in:

 select our () { } # WRONG!  Must name variable with declarator!

The Loop variable

See "SCOPING ISSUES" for full details about the implications of different types of declarations for the loop variable.

The $Reply Variable

When the interactive user responds to the select loop's prompt with a valid input (i.e., a number in the correct range), the variable $Reply is set within the loop to that number. Of course, the actual item selected is usually of great interest than its number in the menu, but there are cases in which access to this number is useful (see "menu_ls.plx" for an example).

OVERVIEW ^

This loop is syntactically similar to Perl's foreach loop, and functionally related, so we'll describe it in those terms.

 foreach $var  ( LIST ) { CODE }

The job of foreach is to run one iteration of CODE for each LIST-item, with the current item's value placed in localized $var (or if the variable is missing, localized $_).

 select  $var  ( LIST ) { CODE }

In contrast, the select loop displays a numbered menu of LIST-items on the screen, prompts for (numerical) input, and then runs an iteration with $var being set that number's LIST-item.

In other words, select is like an interactive, multiple-choice version of a foreach loop. And that's cool! What's not so cool is that select is also the only UNIX shell loop that's been left out of the Perl language. Until now!

This module implements the select loop of the Korn and Bash ("POSIX") shells for Perl. It accomplishes this through Filter::Simple's Source Code Filtering service, allowing the programmer to blithely proceed as if this control feature existed natively in Perl.

The Bash and Korn shells differ slightly in their handling of select loops, primarily with respect to the layout of the on-screen menu. This implementation currently follows the Korn shell version most closely (but see "TODO-LIST" for notes on planned enhancements).

ENHANCEMENTS ^

Although the shell doesn't allow the loop variable to be omitted, for compliance with Perlish expectations, the select loop uses localized $_ by default (as does the native foreach loop). See "SYNTAX" for details.

The interface and behavior of the Shell versions has been retained where deemed desirable, and sensibly modified along Perlish lines elsewhere. Accordingly, the (primary) default LIST is @ARGV (paralleling the Shell's "$@"), menu prompts can be customized by having the script import and set $Prompt (paralleling the Shell's $PS3), and the user's response to the prompt appears in the variable $Reply (paralleling the Shell's $REPLY), localized to the loop.

A deficiency of the shell implementation is the inability of the user to provide a heading for each select menu. Sure, the shell programmer can echo a heading before the loop is entered and the menu is displayed, but that approach doesn't help when an Outer loop is reentered on departure from an Inner loop, because the echo preceding the Outer loop won't be re-executed.

A similar deficiency surrounds the handling of a custom prompt string, and the need to automatically display it on moving from an inner loop to an outer one.

To address these deficiencies, this implementation provides the option of having a heading and prompt bound to each select loop. See "IMPORTS AND OPTIONS" for details.

Headings and prompts are displayed in reverse video on the terminal, if possible, to make them more visually distinct.

Some shell versions simply ignore bad input, such as the entry of a number outside the menu's valid range, or alphabetic input. I can't imagine any argument in favor of this behavior being desirable when input is coming from a terminal, so this implementation gives clear warning messages for such cases by default (see "Warnings" for details).

After a menu's initial prompt is issued, some shell versions don't show it again unless the user enters an empty line. This is desirable in cases where the menu is sufficiently large as to cause preceding output to scroll off the screen, and undesirable otherwise. Accordingly, an option is provided to enable or disable automatic prompting (see "Prompts").

This implementation always issues a fresh prompt when a terminal user submits EOF as input to a nested select loop. In such cases, experience shows it's critical to reissue the menu of the outer loop before accepting any more input.

SCOPING ISSUES ^

If the loop variable is named and provided with a declarator (my, our, or local), the variable is scoped within the loop using that type of declaration. But if the variable is named but lacks a declarator, no declaration is applied to the variable.

This allows, for example, a variable declared as private above the loop to be accessible from within the loop, and beyond it, and one declared as private for the loop to be confined to it:

    select my $loopvar ( ) { }
    print "$loopvar DOES NOT RETAIN last value from loop here\n";
    -------------------------------------------------------------
    my $loopvar;
    select $loopvar ( ) { }
    print "$loopvar RETAINS last value from loop here\n";

With this design, select behaves differently than the native foreach loop, which nowadays employs automatic localization.

    foreach $othervar ( ) { } # variable localized automatically
    print "$othervar DOES NOT RETAIN last value from loop here\n";

    select $othervar ( ) { } # variable in scope, or global
    print "$othervar RETAINS last value from loop here\n";

This difference in the treatment of variables is intentional, and appropriate. That's because the whole point of select is to let the user choose a value from a list, so it's often critically important to be able to see, even outside the loop, the value assigned to the loop variable.

In contrast, it's usually considered undesirable and unnecessary for the value of the foreach loop's variable to be visible outside the loop, because in most cases it will simply be that of the last element in the list.

Of course, in situations where the foreach-like behavior of implicit localization is desired, the programmer has the option of declaring the select loop's variable as local.

Another deficiency of the Shell versions is that it's difficult for the programmer to differentiate between a select loop being exited via last, versus the loop detecting EOF on input. To correct this situation, the variable $Eof can be imported and checked for a TRUE value upon exit from a select loop (see "Eof Detection").

IMPORTS AND OPTIONS ^

Syntax

 use Shell::POSIX::Select (
     '$Prompt',      # to customize per-menu prompt
     '$Heading',     # to customize per-menu heading
     '$Eof',         # T/F for Eof detection
  # Variables must come first, then key/value options
     prompt   => 'Enter number of choice:',  # or 'whatever:'
     style    => 'Bash',     # or 'Korn'
     warnings => 1,          # or 0
     debug    => 0,          # or 1-5
     logging  => 0,          # or 1
     testmode => <unset>,    # or 'make', or 'foreach'
 );

NOTE: The values shown for options are the defaults, except for testmode, which doesn't have one.

Prompts

There are two ways to customize the prompt used to solicit choices from select menus; through use of the prompt option, which applies to all loops, or the $Prompt variable, which can be set independently for each loop.

The prompt option

The prompt option is intended for use in programs that either contain a single select loop, or are content to use the same prompt for every loop. It allows a custom interactive prompt to be set in the use statement.

The prompt string should not end in a whitespace character, because that doesn't look nice when the prompt is highlighted for display (usually in reverse video). To offset the cursor from the prompt's end, one space is inserted automatically after display highlighting has been turned off.

If the environment variable $ENV{Shell_POSIX_Select_prompt} is present, its value overrides the one in the use statement.

The default prompt is "Enter number of choice:". To get the same prompt as provided by the Korn or Bash shell, use prompt =>> Korn or prompt => Bash.

The $Prompt variable

The programmer may also modify the prompt during execution, which may be desirable with nested loops that require different user instructions. This is accomplished by importing the $Prompt variable, and setting it to the desired prompt string before entering the loop. Note that imported variables have to be listed as the initial arguments to the use directive, and properly quoted. See "order.plx" for an example.

NOTE: If the program's input channel is not connected to a terminal, prompting is automatically disabled (since there's no point in soliciting input from a pipe!).

$Heading

The programmer has the option of binding a heading to each loop's menu, by importing $Heading and setting it just before entering the associated loop. See "order.plx" for an example.

$Eof

A common concern with the Shell's select loop is distinguishing between cases where a loop ends due to EOF detection, versus the execution of break (like Perl's last). Although the Shell programmer can check the $REPLY variable to make this distinction, this implementation localizes its version of that variable ($Reply) to the loop, obviating that possibility.

Therefore, to make EOF detection as convenient and easy as possible, the programmer may import $Eof and check it for a TRUE value after a select loop. See "lc_filename.plx" for a programming example.

Styles

The style options Korn and Bash can be used to request a more Kornish or Bashlike style of behavior. Currently, the only difference is that the former disables, and the latter enables, prompting for every input. A value can be provided for the style option using an argument of the form style => 'Korn' to the use directive. The default setting is Bash. If the environment variable $ENV{Shell_POSIX_Select_style} is set to Korn or Bash, its value overrides the one provided with the use statement.

Warnings

The warnings option, whose values range from 0 to 1, enables informational messages meant to help the interactive user provide correct inputs. The default setting is 1, which provides warnings about incorrect responses to menu prompts (non-numeric, out of range, etc.). Level 0 turns these off.

If the environment variable $ENV{Shell_POSIX_Select_warnings} is present, its value takes precedence.

Logging

The logging option, whose value ranges from 0 to 1, causes informational messages and source code to be saved in temporary files (primarily for debugging purposes).

The default setting is 0, which disables logging.

If the environment variable $ENV{Shell_POSIX_Select_logging} is present, its value takes precedence.

Debug

The debug option, whose values range from 0 to 9, enables informational messages to aid in identifying bugs. If the environment variable $ENV{Shell_POSIX_Select_debug} is present, and set to one of the acceptable values, it takes precedence.

This option is primarly intended for the author's use, but users who find bugs may want to enable it and email the output to "AUTHOR". But before concluding that the problem is truly a bug in this module, please confirm that the program runs correctly with the option testmode => foreach enabled (see "Testmode").

Testmode

The testmode option, whose values are 'make' and 'foreach', changes the way the program is executed. The 'make' option is used during the module's installation, and causes the program to dump the modified source code and screen display to files, and then stop (rather than interacting with the user).

If the environment variable $ENV{Shell_POSIX_Select_testmode} is present, and set to one of the acceptable values, it takes precedence.

With the foreach option enabled, the program simply translates occurrences of select into foreach, which provides a useful method for checking that the program is syntactically correct before any serious filtering has been applied (which can introduce syntax errors). This works because the two loops, in their full forms, have identical syntax.

Note that before you use testmode => foreach, you must fill in any missing parts that are required by foreach.

For instance,

select () {}

must be rewritten as follows, to explicitly show "@ARGV" (assuming it's not in a subroutine) and "print":

foreach (@ARGV) { print; }

ADDITIONAL EXAMPLES ^

NOTE: All non-trivial programming examples shown in this document are distributed with this module, in the Scripts directory. See "ELEMENTARY EXAMPLES" for simpler uses of select.

pick_file.plx

This program lets the user choose filenames to be sent to the output. It's sort of like an interactive Perl grep function, with a live user providing the filtering service. As illustrated below, it could be used with Shell command substitution to provide selected arguments to a command.

    use Shell::POSIX::Select  (
        prompt => 'Pick File(s):' ,
        style => 'Korn'  # for automatic prompting
    );
    select ( <*> ) { }

Screen

    lp `pick_file`>   # Using UNIX-like OS

    1) memo1.txt   2) memo2.txt   3) memo3.txt
    4) junk1.txt   5) junk2.txt   6) junk3.txt

    Pick File(s): 4
    Pick File(s): 2
    Pick File(s): ^D

    request id is yumpy@guru+587

browse_images.plx

Here's a simple yet highly useful script. It displays a menu of all the image files in the current directory, and then displays the chosen ones on-screen using a backgrounded image viewer. It uses Perl's grep to filter-out filenames that don't end in the desired extensions.

    use Shell::POSIX::Select ;

    $viewer='xv';  # Popular image viewer

    select ( grep /\.(jpg|gif|tif|png)$/i, <*> ) {
        system "$viewer $_ &" ;     # run viewer in background
    }

perl_man.plx

Back in the olden days, we only had one Perl man-page. It was voluminous, but at least you knew what argument to give the man command to get the documentaton.

Now we have over a hundred Perl man pages, with unpredictable names that are difficult to remember. Here's the program I use that allows me to select the man-page of interest from a menu.

 use Shell::POSIX::Select ;

 # Extract man-page names from the TOC portion of the output of "perldoc perl"
 select $manpage ( sort ( `perldoc perl` =~ /^\s+(perl\w+)\s/mg) ) {
     system "perldoc '$manpage'" ;
 }

Screen

  1) perl5004delta     2) perl5005delta     3) perl561delta    
  4) perl56delta       5) perl570delta      6) perl571delta    
 . . .

(This large menu spans multiple screens, but all parts can be accessed using your normal terminal scrolling facility.)

 Enter number of choice: 6

 
 PERL571DELTA(1)       Perl Programmers Reference Guide 

 NAME
        perl571delta - what's new for perl v5.7.1

 DESCRIPTION
        This document describes differences between the 5.7.0
        release and the 5.7.1 release.
 . . .

pick.plx

This more general pick-ing program lets the user make selections from arguments, if they're present, or else input, in the spirit of Perl's -n invocation option and <> input operator.

 use Shell::POSIX::Select ;

 BEGIN {
     if (@ARGV) {
         @choices=@ARGV ;
     }
     else { # if no args, get choices from input
         @choices=<STDIN>  or  die "$0: No data\n";
         chomp @choices ;
         # STDIN already returned EOF, so must reopen
         # for terminal before menu interaction
         open STDIN, "/dev/tty"  or
             die "$0: Failed to open STDIN, $!" ;  # UNIX example
     }
 }
 select ( @choices ) { }   # prints selections to output

Sample invocations (UNIX-like system)

    lp `pick *.txt`    # same output as shown for "pick_file"

    find . -name '*.plx' -print | pick | xargs lp  # includes sub-dirs

    who |
        awk '{ print $1 }' |        # isolate user names
            pick |                  # select user names
                Mail -s 'Promote these people!'  boss

delete_file.plx

In this program, the user selects a filename to be deleted. The outer loop is used to refresh the list, so the file deleted on the previous iteration gets removed from the next menu. The outer loop is labeled (as OUTER), so that the inner loop can refer to it when necessary.

 use Shell::POSIX::Select (
     '$Eof',   # for ^D detection
     prompt=>'Choose file for deletion:'
 ) ;

 OUTER:
     while ( @files=<*.py> ) { # collect serpentine files
         select ( @files ) {   # prompt for deletions
             print STDERR  "Really delete $_? [y/n]: " ;
             my $answer = <STDIN> ;     # ^D sets $Eof below
             defined $answer  or  last OUTER ;  # exit on ^D
             $answer eq "y\n"  and  unlink  and  last ;
         }
         $Eof and last;
 }

lc_filename.plx

This example shows the benefit of importing $Eof, so the outer loop can be exited when the user supplies ^D to the inner one.

Here's how it works. If the rename succeeds in the inner loop, execution of last breaks out of the select loop; $Eof will then be evaluated as FALSE, and the while loop will start a new select loop, with a (depleted) filename menu. But if the user presses ^D to the menu prompt, $Eof will test as TRUE, triggering the exit from the while loop.

 use Shell::POSIX::Select (
     '$Eof' ,
     prompt => 'Enter number (^D to exit):'
     style => 'Korn'  # for automatic prompting
 );

 # Rename selected files from current dir to lowercase
 while ( @files=<*[A-Z]*> ) {   # refreshes select's menu
     select ( @files ) { # skip fully lower-case names
         if (rename $_, "\L$_") {
             last ;
         }
         else {
             warn "$0: rename failed for $_: $!\n";
         }
     }
     $Eof  and  last ;   # Handle ^D to menu prompt
 }

Screen

 lc_filename.plx

 1) Abe.memo   2) Zeke.memo
 Enter number (^D to exit): 1

 1) Zeke.memo
 Enter number (^D to exit): ^D

order.plx

This program sets a custom prompt and heading for each of its two loops, and shows the use of a label on the outer loop.

 use Shell::POSIX::Select qw($Prompt $Heading);
 
 $Heading="\n\nQuantity Menu:";
 $Prompt="Choose Quantity:";
 
 OUTER:
   select my $quantity (1..4) {
      $Heading="\nSize Menu:" ;
      $Prompt='Choose Size:' ;
  
      select my $size ( qw (L XL) ) {
          print "You chose $quantity units of size $size\n" ;
          last OUTER ;    # Order is complete
      }
   }

Screen

 order.plx

 Quantity Menu:
 1)  1    2)  2    3)  3    4)  4
 Choose Quantity: 4

 Size Menu:
 1) L   2) XL
 Choose Size: ^D       (changed my mind about the quantity)

 Quantity Menu:
 1)  1    2)  2    3)  3    4)  4
 Choose Quantity: 2

 Size Menu:
 1)  L    2)  XL
 Choose Size: 2
 You chose 2 units of size XL

browse_records.plx

This program shows how you can implement a "record browser", that builds a menu from the designated field of each record, and then shows the record associated with the selected field.

To use a familiar example, we'll browse the UNIX password file by user-name.

 use Shell::POSIX::Select ( style => 'Korn' );
 
 if (@ARGV != 2  and  @ARGV != 3) {
     die "Usage: $0 fieldnum filename [delimiter]" ;
 }
 
 # Could also use Getopt:* module for option parsing
 ( $field, $file, $delim) = @ARGV ;
 if ( ! defined $delim ) {
     $delim='[\040\t]+' # SP/TAB sequences
 }
 
 $field-- ;  # 2->1, 1->0, etc., for 0-based indexing
 
 foreach ( `cat "$file"` ) {
     # field is the key in the hash, value is entire record
     $f2r{ (split /$delim/, $_)[ $field ] } = $_ ;
 }
 
 # Show specified fields in menu, and display associated records
 select $record ( sort keys %f2r ) {
     print "$f2r{$record}\n" ;
 }

Screen

 browsrec.plx  '1'  /etc/passwd  ':'

  1) at     2) bin       3) contix   4) daemon  5) ftp     6) games
  7) lp     8) mail      9) man     10) named  11) news   12) nobody
 13) pop   14) postfix  15) root    16) spug   17) sshd   18) tim

 Enter number of choice: 18

 tim:x:213:100:Tim Maher:/home/tim:/bin/bash

 Enter number of choice: ^D

menu_ls.plx

This program shows a prototype for a menu-oriented front end to a UNIX command, that prompts the user for command-option choices, assembles the requested command, and then runs it.

It employs the user's numeric choice, stored in the $Reply variable, to extract from an array the command option associated with each option description.

 use Shell::POSIX::Select qw($Heading $Prompt $Eof) ;

 # following avoids used-only once warning
 my ($type, $format) ;
 
 # Would be more Perlish to associate choices with options
 # via a Hash, but this approach demonstrates $Reply variable
 
 @formats = ( 'regular', 'long' ) ;
 @fmt_opt = ( '',        '-l'   ) ;
 
 @types   = ( 'only non-hidden', 'all files' ) ;
 @typ_opt = ( '',                '-a' ,      ) ;
 
 print "** LS-Command Composer **\n\n" ;
 
 $Heading="\n**** Style Menu ****" ;
 $Prompt= "Choose listing style:" ;
 OUTER:
   select $format ( @formats ) {
       $user_format=$fmt_opt[ $Reply - 1 ] ;
   
       $Heading="\n**** File Menu ****" ;
       $Prompt="Choose files to list:" ;
       select $type ( @types ) {   # ^D restarts OUTER
           $user_type=$typ_opt[ $Reply - 1 ] ;
           last OUTER ;    # leave loops once final choice obtained
       }
   }
 $Eof  and  exit ;   # handle ^D to OUTER
 
 # Now construct user's command
 $command="ls  $user_format  $user_type" ;
 
 # Show command, for educational value
 warn "\nPress <ENTER> to execute \"$command\"\n" ;

 # Now wait for input, then run command
 defined <>  or  print "\n"  and  exit ;    
 
 system $command ;    # finally, run the command

Screen

 menu_ls.plx
 
 ** LS-Command Composer **
 
 1) regular    2) long
 Choose listing format: 2
 
 1) only non-hidden   2) all files
 Choose files to list:  2 
 
 Press <ENTER> to execute "ls -l -a" <ENTER>

 total 13439
 -rw-r--r--    1 yumpy   gurus    1083 Feb  4 15:41 README
 -rw-rw-r--    6 yumpy   gurus     277 Dec 17 14:36 .exrc.mmkeys
 -rw-rw-r--    7 yumpy   gurus     285 Jan 16 18:45 .exrc.podkeys
 $

BUGS ^

UNIX Orientation

I've been a UNIX programmer since 1976, and a Linux proponent since 1992, so it's most natural for me to program for those platforms. Accordingly, this early release has some minor features that are only allowed, or perhaps only entirely functional, on UNIX-like systems. I'm open to suggestions on how to implement some of these features in a more portable manner.

Some of the programming examples are also UNIX oriented, but it should be easy enough for those specializing on other platforms to make the necessary adapations. 8-}

Terminal Display Modes

These have been tested under UNIX/Linux, and work as expected, using tput. When time permits, I'll convert to a portable implementation that will support other OSs.

Incorrect Line Numbers in Warnings

Because this module inserts new source code into your program, Perl messages that reference line numbers will refer to a different source file than you wrote. For this reason, only messages referring to lines before the first select loop in your program will be correct.

If you're on a UNIX-like system, by enabling the debugging and logging options (see "Debug" and "Logging"), you can get an on-screen report of the proper offset to apply to interpret the line numbers of the source code that gets dumped to the /tmp/SELECT_source file. Of course, if everything works correctly, you'll have little reason to look at the source. 8-}

Comments can Interfere with Filtering

Because of the way Filter::Simple works, ostensibly "commented-out" select loops like the following can actually break your program:

 # select (@ARGV)
 # { ; }
 select (@ARGV) { ; }

A future version of Filter::Simple (or more precisely Text::Balanced, on which on which it depends) may correct this problem.

In any case, there's an easy workaround for the commented-out select loop problem; just change select into eslect when you comment it out, and there'll be no problem.

For other problems involving troublesome text within comments, see "Failure to Identify select Loops".

Failure to Identify select Loops

When a properly formed select loop appears in certain contexts, such as before a line containing certain patterns of dollar signs or quotes, it will not be properly identified and translated into standard Perl.

The failure of the filtering routine to rewrite the loop causes the compiler to issue the following fatal error when it sees the { following the (LIST):

syntax error at filename line X, near ") {"

This of course prevents the program from running.

The problem is either a bug in Filter::Simple, or one of the modules on which it depends. Until this is resolved, you may be able to handle such cases by explicitly turning filtering off before the offending code is encountered, using the no directive:

    use Shell::POSIX::Select;     # filtering ON
    select (@names) { print ; }

    no Shell::POSIX::Select;      # filtering OFF
    # $X$

Restrictions on Loop-variable Names

Due to a bug in most versions of Text::Balanced, loop-variable names that look like Perl operators, including $m, $a, $s, $y, $tr, $qq, $qw, $qr, and $qx, and possibly others, cause syntax errors. Newer versions of that module (unreleased at the time of this writing) have corrected this problem, so download the latest version if you must use such names.

Please Report Bugs!

This is a non-trivial program, that does some fairly complex parsing and data munging, so I'm sure there are some latent bugs awaiting your discovery. Please share them with me, by emailing the offending code, and/or the diagnostic messages enabled by the debug option setting (see "IMPORTS AND OPTIONS").

TODO-LIST ^

More Shell-like Menus

In a future release, there could be options for more accurately emulating Bash and Korn-style behavior, if anybody cares (the main difference is in how the items are ordered in the menus).

More Extensive Test Suite

More tests are needed, especially for the complex and tricky cases.

MODULE DEPENDENCIES ^

 File::Spec::Functions
 Text::Balanced
 Filter::Simple

EXPORTS: Default ^

 $Reply

This variable is localized to each select loop, and provides the menu-number of the most recent valid selection. For an example of its use, see "menu_ls.plx".

EXPORTS: Optional ^

 $Heading
 $Prompt
 $Eof

See "IMPORTS AND OPTIONS" for details.

SCRIPTS ^

 browse_images
 browse_jpeg
 browse_records
 delete_file
 lc_filename
 long_listem
 menu_ls
 order
 perl_man
 pick
 pick_file

AUTHOR ^

 Tim Maher
 Consultix
 yumpy@cpan.org
 http://www.teachmeperl.com
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ACKNOWLEDGEMENTS ^

I probably never would have even attempted to write this module if it weren't for the provision of Filter::Simple by Damian Conway, which I ruthlessly exploited to make a hard job easy.

The Damian also gave useful tips during the module's development, for which I'm grateful.

I definitely wouldn't have ever written this module, if I hadn't found myself writing a chapter on Looping for my upcoming Manning Publications book, and once again lamenting the fact that the most friendly Shell loop was still missing from Perl. So in a fit of zeal, I vowed to rectify that oversight!

I hope you find this module as useful as I do! 8-}

For more examples of how this loop can be used in Perl programs, watch for my upcoming book, Minimal Perl: for Shell Users and Programmers (see http://teachmeperl.com/mp4sh.html) in early fall, 2003.

SEE ALSO ^

 man ksh     # on UNIX or UNIX-like systems

 man bash    # on UNIX or UNIX-like systems

DON'T SEE ALSO ^

perldoc -f select, which has nothing to do with this module (the names just happen to match up).

VERSION ^

 This document describes version 0.05.

LICENSE ^

Copyright (C) 2002-2003, Timothy F. Maher. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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