Provided by: libterm-query-perl_2.0-9_all 
NAME
Term::Query - Table-driven query routine.
SYNOPSIS
"use Term::Query"
"qw( query query_table query_table_set_defaults query_table_process );"
"$result = query $prompt, $flags, [ $optional_args ];"
"$ok = query_table \@array;"
"query_table_set_defaults \@array;"
"$ok = query_table_process \@array, \&flagsub, \&querysub;"
DESCRIPTION
query
The query subroutine fulfills the need for a generalized question-response subroutine, with programmatic
defaulting, validation, condition and error checking.
Given $prompt and $flags, and possibly additional arguments, depending upon the characters in $flags,
query issues a prompt to STDOUT and solicits input from STDIN. The input is validated against a set of
test criteria as configured by the characters in $flags; if any of the tests fail, an error message is
noted, and the query is reattempted.
When STDIN is not a tty (not interactive), prompts are not issued, and errors cause a return rather than
attempting to obtain more input. This non-interactive behaviour can be disabled by setting the variable
$Foce_Interactive as below:
$Term::Query::Force_Interactive = 1;
When $Force_Interactive is a non-null, non-zero value, query will issue prompts, error messages, and ask
for additional input even when the input is not interactive.
query_table
The query_table subroutine performs multiple queries, by invoking query, setting associated variables
with the results of each query. Prompts, flags, and other arguments for each query are given in an
array, called a query table, which is passed to the query_table subroutine by reference.
query_table_set_defaults
The query_table_set_defaults subroutine causes any variables named in the given query table array to be
assigned their corresponding default values, if any. This is a non-interactive subroutine.
query_table_process
A general interface to processing a query table is available with the query_table_process subroutine. It
accepts a query table array, and two subroutine references, a &flagsub and a &querysub. The &flagsub is
invoked on each each flag character given in the $flags argument of the query table (see below). The
&querysub is invoked for each query in the query table.
The query_table and query_table_set_defaults subroutines both use query_table_process to perform their
functions.
Query Table
The format of the query table array passed to query_table, query_table_set_defaults, and
query_table_process subroutines is:
@array = ( $prompt1, $flags1, [ $arglist1, ... ],
$prompt2, $flags2, [ $arglist2, ... ],
...
$promptN, $flagsN, [ $arglistN, ... ] );
In English, there are three items per query: a prompt string, a flags string, and an array of arguments.
Note that the syntax used above uses "[ ... ]" to denote a Perl 5 anonymous array, not an optional set of
arguments. Of course, if there are no arguments for a particular query, the corresponding anonymous
array can be the null string or zero.
The query table design is such that a query table can be created with a set of variables, their defaults,
value constraints, and help strings, and it can be used to both initialize the variables' values and to
interactively set their new values. The query_table_set_defaults subroutine performs the former, while
query_table does the latter.
Flag Characters
With typical usage, given $prompt and $flags, query prints $prompt and then waits for input from the
user. The handling of the response depends upon the flag characters given in the $flags string.
The flag characters indicate the type of input, how to process it, acceptable values, etc. Some flags
simply indicate the type or processing of the input, and do not require additional arguments. Other
flags require that subsequent arguments to the query subroutine be given. The arguments must be given in
the same order as their corresponding flag characters.
The ordering of the flags in the $flags argument is important -- it determines the ordering of the tests.
For example, if both the a and m flags are given as "am", then this indicates that an after subroutine
call should be performed first, followed by a regular expression match test.
All tests are applied in the order given in the $flags until a particular test fails. When a test fails,
an error message is generated and the input is reattempted, except in the case of the I flag.
Flag Characters Without Arguments
i The input must be an integer.
n The input must be a number, real or integer.
Y The input is a "yes" or "no", with a default answer of "yes".
N The input is a "yes" or "no", with a default answer of "no".
r Some input is required; an empty response will be refused. This option is only meaningful when
there is no default input (see the d flag character below).
s Strip and squeeze the input. Leading and trailing blanks are eliminated, and embedded whitespace is
"squeezed" to single blank characters. This flag is implied by the k and K flags.
H Do not treat input of ? as a request for help. This disables automatic help, unless implemented
with the after (a flag) subroutine.
Flag Characters With Arguments
The following flag characters indicate the presence of an argument to query. The arguments must occur in
the same order as their corresponding flag characters. For example, if both the V and h flags are given
as "Vh", then the first argument must be the variable name, and the next the help string, in that order.
a \&after
The next argument is the after subroutine, to be invoked after the input has been solicited. This
feature provides for an "open ended" input validation, completely at the control of the user of the
Query module. The after subroutine is invoked in this manner:
&$after( \$input );
If the after sub returns an "undef", then query processing stops with an immediate "undef" return
value.
If the after sub returns a null or zero value, then the input is rejected and resolicted. No error
messages are displayed except the "Please try again." message.
Since the after sub has the reference to the $input variable, it is free to change the value of
input indirectly; ie:
$$input = $some_new_value;
b \&before
The next argument is the before subroutine, to be invoked before any input is attempted. If the
before sub returns a non-null, non-zero value, the current query will be attempted. If a null or
zero value is returned, the current query will be abandoned, with a null return.
This feature, used in a query table, allows for selective queries to be programmed by using before
subs on the optional queries. For example, using the following anonymous sub as the b flag
argument:
sub { $> == 0; }
will cause the corresponding query to only be issued for the "root" user.
The ordering of the b flag in the $flags argument is unimportant, since, by definition, this test is
always performed before attempting any input.
d $default
The next argument is the default input. This string is used instead of an empty response from the
user. The default value can be a scalar value, a reference to a scalar value, or a reference to a
subroutine, which will be invoked for its result only if a default value is needed (no input is
given).
h $help_string
The next argument is the help string, which is printed in response to an input of "?". In order to
enter a ? as actual text, it must be prefixed with a backslash: "\".
k \@array
The next argument is a reference to an array of allowable keywords. The input is matched against
the array elements in a case-insensitive manner, with unambiguous abbreviations allowed. This flag
implies the s flag.
The matching can be made case-sensitive by setting the following variable prior to the invocation of
query:
$Query::Case_sensitive = 1;
By default, this variable is null.
K \@array
The next argument is a reference to an array of disallowed keywords In this case, for the input to
be unacceptable, it must match exactly, case-insensitive, one of the array elements. This flag
implies the s flag.
The k option is useful for soliciting new, unique keywords to a growing list. Adding new fields to
a database, for example.
The matching can be made case-sensitive by setting the $Query::Case_sensitive variable (see above).
l $maxlen
The next argument specifies the maximum length of the input.
m $regular_expression
The next argument specifies a regular expression pattern against which the input will be matched.
I $reference
The next argument is the input: either a simple scalar value, or a reference to a value, such as a
"SCALAR" variable reference (eg: "\$somevar"), or a "CODE" reference (eg: "sub {..}"). In any case,
the resulting value is used as input instead of reading from STDIN.
If the input returned by the reference does not match other constraints, additional input is not
attempted. An error message is noted, and an "undef" return is taken.
This option is handy for applications which have already acquired the input, and wish to use the
validation features of "query".
It is also useful to embed a query definition in a query table which does not actually perform a
query, but instead does a variable assignment dynamically, using the I reference value.
J $reference
The next argument is the input reference, as with the I flag, except that if the input fails any of
the constraints, additional input is solicited from the input. In other words, the J flag sets a
one-time only input reference. Think of it as jumping into the query loop with an initial input.
V variable_name_or_ref
The next argument is the variable name or reference to receive the validated input as its value.
This option, and its corresponding variable name, would normally be present on all entries used with
query_table in order to retain to the values resulting from each query.
The value can either be a string representing the variable name, or a reference to a variable, eg:
"\$some_var".
Details
The query processing proceeds basically in the same order as defined by the flags argument, with some
exceptions. For example, the before subroutine is always performed prior to input.
There are implicit precedences in the ordering of some of the flag tests. Generally, flags have their
corresponding tests performed in the same order as the given flags. Some flag tests, however, require
that other flags' tests be performed beforehand in order to be effective. For example, when given the k
flag and an s flag, stripping the input would only be effective if the strip were done on the input
before testing the input against the keyword table. In other words, the s flag has precedence over the k
flag. If the user supplies the flags string as "ks", the effective ordering would still be "sk".
The table below indicates the precedences of the flag tests:
Given Flag Flags With Higher Precedence
========== ================================
i (int) s (strip), d (default), h (help)
k (key) s (strip), d (default), h (help)
K (nonkey) s (strip), d (default), h (help)
l (maxlen) d (default), h (help)
m (match) d (default), h (help)
n (numeric) s (strip), d (default), h (help)
N (no) s (strip), d (default), h (help)
r (required) d (default), h (help)
s (strip) d (default), h (help)
Y (yes) s (strip), d (default), h (help)
Except for the implied precedence indicated in the table above, the ordering of the flag tests proceeds
in the same order as given in the flags argument.
Excepting the precedences above, query processing proceeds generally as described below.
• If the b flag was given, the "before" subroutine is invoked as a "pre-input" test. If the sub
returns a 0, empty string, or undef, the query is abandoned. Otherwise, processing continues.
• If the I or J flags were given, then input is obtained, without prompting, from the associated
reference. If the reference type is "CODE", then it is invoked and the resulting return value is
used as the input. Otherwise the reference is evaluated in a scalar context and used as the input.
The J flag test is only done once, on the first entry into the input loop.
• In the absence either the I or J flags, "query" will issue the given prompt and obtain input from
STDIN. If an EOF occurs, an "undef" value will result.
• The input is examined for "null" input (that is, the empty string), and processing quits in this
case. Since most input is obtained from STDIN, a null input indicates an end-of-file (EOF). If the
input is not null, a terminating newline is removed, and the input testing continues. At this
point, an empty input string does not indicate an EOF.
• If the s, k, or K flags were given, the input is trimmed of leading and trailing blanks, and all
whitespace is "squeezed" to single blanks.
• If the input is an empty response, and there is a default input (d flag), use it instead.
• Unless the H flag is given, if the input is the character "?" with nothing else, then print some
helpful information. If the user had supplied a help string, it is printed, otherwise the message:
You are being asked "$prompt"
is displayed. Also, some information about the expected response, according to any given flag
characters, is displayed. Finally, the user is returned to the prompt, and given another
opportunity to enter a response.
• If input is required (indicated by the r flag), and if the input is empty, produce an error message,
and query again.
• If there was a a flag, the corresponding after subroutine is invoked with the input reference as its
argument. If the subroutine returns a non-null, non-zero value, the input succeeds, otherwise it
fails. It is up to the after subroutine to display any appropriate error messages.
• If the query was flagged Y or N, match the input against the pattern:
/^(y(es?)?|no?)$/i
If the match fails, print an error message, and query again. When the match succeeds, replace the
input with the complete word "yes" or "no";
• If an integer response is required (i flagged), check for integer input. If not, print an error,
and query again. A successful integer input is returned.
• If a numeric response is required (n flagged), check for proper numeric input (either integer or
real format). Errors produce a warning, and another query.
• If the query was given a keyword table (flagged with k), the input is matched against the allowable
keyword list. If an exact match is found, the keyword is returned as the input. Failing an exact
match, an abbreviation search is performed against the keywords. If a single match is found, it is
returned as the input. If no match is found, an error message is produced, and the user is returned
to the query to try again. Otherwise, the input was ambiguous, an error noted showing the matches,
and the user is queried again.
The matching is case-insensitive or not, according to the value of the variable
$Query::Case_sensitive, which is nil, by default. The variable may be set by the user to change the
matching from case-insensitive to case-sensitive.
• If the query was given an unacceptable keyword list (flagged with K), the input is compared against
the unacceptable keywords. If it matches any keywords exactly, an error is noted, and the query is
performed again.
The matching is case-insensitive by default. Set the variable $Query::Case_sensitive to a non-null,
non-zero value to make the keyword matching case-sensitive.
• If the query was m flagged with a Perl regular expression pattern, then the input is matched against
the pattern. Failures are noted with an error message, and the query reattempted.
• If the query was l flagged with a maximum input length, the length of the input is checked against
the maximum. A length violation is noted with an error message and the user is queried again.
• If the query has a variable defined with the V flag, the variable is assigned the input string.
This is always done last, after and only if all tests are successful.
If the variable is a string name and not qualified with a package name (ie: $foo::variable), then
the variable is qualified at the level outside of the Query.pm module.
• Finally, having passed whatever conditions were flagged, the input is returned to the user.
EXAMPLE
The following are typical usage samples:
• To perform a simple "yes" or "no" query, with "no" as the default answer:
$ans = &query("Do you wish to quit? (yn)",'N');
• An equivalent alternative is:
query "Do you wish to quit? (yn)", 'NV', \$ans;
• To perform the same query, with some supplied helpful information:
$ans = &query("Do you wish to quit? (yn)",'Nh',<<'EOF');
You are being asked if you wish to quit. If you answer "yes",
then all changes will be lost. An answer of "no", will allow
you to return to continue making changes.
EOF
• To solicit an integer input:
$mode = &query("Please enter the file mode:",'idh','644',<<'EOF');
Please enter the 3 digit numeric file mode; if you are unsure
of how the file mode is used, please see the man page for "chmod".
EOF
• To solicit one of several keywords:
@keys = split(' ','SGI DEC IBM Sun HP Apple');
$vendor = &query('Please enter a vendor:','rkd',\@keys,'SGI');
• To solicit a new, unique keyword to be used as a database field name, with a regexp pattern to check
it against:
@fields = split(' ','Index Vendor Title'); # existing fields
$newfield = &query('New field name:','rKm',\@fields,'^\w+$');
ENVIRONMENT
COLUMNS
This variable is used to control the width of output when listing the keyword arrays. If not
defined, 80 is used by default.
DEPENDENCIES
Carp.pm
Used to produce usage error messages.
Array::PrintCols::print_cols
Used to produce displays of the keyword arrays.
FILES
None.
AUTHOR
Copyright (C) 1995 Alan K. Stebbens <aks@hub.ucsb.edu>
This program is free software; you can redistribute it and/or modify it under the terms of the GNU
General Public License as published by the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write
to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
DIAGNOSTICS
Input is required.
Issued when an empty response is given, and there is no default input.
Please answer with 'yes' or 'no', or enter '?' for help.
Issued for Y or N flagged queries, and the input is not reconizeable.
Please enter an integer number.
Printed when non-integer input is given for i flagged queries.
Please enter a number, real or integer.
Printed when non-numeric input is given for n flagged queries.
The input '$input' is ambiguous; it matches the following:
Issued in response to k flagged queries with input which matches more than one of the allowed
keywords.
The input '$input' fails to match any of the allowed keywords:
Printed when input to a k flagged query does not match any of the keywords.
The input '%s' matches a disallowed keyword '%s'.
Printed when the input matches one of the unacceptable keywords given on a K flagged query.
'%s' fails to match '%s'
This results from input failing to match the regular expression given on a m flagged query.
Input is %d characters too long; cannot exceed %d characters.
The length of the input exceeded the maximum length given with the l flag argument.
Please try again, or enter '?' for help.
query: The k flag needs an array reference.
The next argument in the argument list to query wasn't an array reference.
query: The K flag needs an array reference.
The next argument in the argumentlist to query wasn't an array reference.