SPUG:Shell::POSIX::Select released; need testers!
Tim Maher
tim at consultix-inc.com
Tue May 6 14:29:03 CDT 2003
SPUGsters,
My long awaited module Shell::POSIX::Select has now been released.
It's a very full-featured, enhanced version of the select loop of
the POSIX shells for Perl, implemented through source filtering.
And it works -- at least for me! (details below).
Here's an example of what it lets you do, excerpted from the man-page,
from a script I use all the time:
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 TOC portion of "perldoc perl" output
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
. . .
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.
. . .
***************************************************************
Unfortunately, it seems that "make test" is failing for some people,
although of course it works perfectly well on the various Linux
and Solaris boxes in my collection. 8-{
So I'd appreciate it if some of you could download the module and
try to install it, and tell me what happens. It's theoretically
possible that the test procedure could report errors and the module
still work perfectly well, so if you do see errors, please try to
run one of the Scripts/*.plx scripts with appropriate changes made
to your PERL5LIB variable, and tell me what happens.
(NOTE: Some of those scripts will need arguments to do anything
interesting.)
-Tim
*------------------------------------------------------------*
| Tim Maher (206) 781-UNIX (866) DOC-PERL (866) DOC-UNIX |
| CEO, JAWCAR ("Just Another White Camel Award Recipient") |
| tim at Consultix-Inc.Com TeachMeUnix.Com TeachMePerl.Com |
*+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-*
| Watch for my Book: "Minimal Perl for Shell Programmers" |
*------------------------------------------------------------*
-------------- next part --------------
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 indicate 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 at 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 *se*lect into *es*lect 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,
it will not be properly identified and translated into standard
Perl. The following is such an example:
use Shell::POSIX::Select;
select (@names) { print ; }
# $X$
The failure of the filtering routine to rewrite the loop causes
the compiler to throw a fatal error, which prevents the program
from running. This is either due to a bug in Filter::Simple, or
one of the modules on which it depends. Until this is resolved,
you can 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 "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 at 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 0.03.
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.
More information about the spug-list
mailing list