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 $_, "local"ized 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 "local"ized $var
(or if the variable is missing, "local"ized $_).
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
"local"ized $_ by default (as does the native "foreach"
loop). See "SYNTAX" for details.
The interface and behavior of the Shell versions has been retained where deemed
desirable, and sensibly modified along Perlish lines elsewhere. Accordingly,
the (primary) default LIST is
@ARGV (paralleling the
Shell's
"$@"), 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 ), "local"ized 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
"local"ization 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
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-}
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¶
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 "local"ized 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
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.