FM / pod

/usr/share/perl5/pod

Name	Size	Mode	Actions
perl.pod	16667	0644	edit dl rm
perl56delta.pod	107201	0644	edit dl rm
perl58delta.pod	115165	0644	edit dl rm
perl561delta.pod	124713	0644	edit dl rm
perl581delta.pod	38060	0644	edit dl rm
perl582delta.pod	4470	0644	edit dl rm
perl583delta.pod	6335	0644	edit dl rm
perl584delta.pod	7363	0644	edit dl rm
perl585delta.pod	5889	0644	edit dl rm
perl586delta.pod	4651	0644	edit dl rm
perl587delta.pod	8357	0644	edit dl rm
perl588delta.pod	25281	0644	edit dl rm
perl589delta.pod	53904	0644	edit dl rm
perl5004delta.pod	56240	0644	edit dl rm
perl5005delta.pod	34283	0644	edit dl rm
perl5100delta.pod	55533	0644	edit dl rm
perl5101delta.pod	43888	0644	edit dl rm
perl5120delta.pod	89271	0644	edit dl rm
perl5121delta.pod	10141	0644	edit dl rm
perl5122delta.pod	9603	0644	edit dl rm
perl5123delta.pod	4100	0644	edit dl rm
perl5124delta.pod	3672	0644	edit dl rm
perl5125delta.pod	7683	0644	edit dl rm
perl5140delta.pod	144325	0644	edit dl rm
perl5141delta.pod	7966	0644	edit dl rm
perl5142delta.pod	6892	0644	edit dl rm
perl5143delta.pod	7760	0644	edit dl rm
perl5144delta.pod	6327	0644	edit dl rm
perl5160delta.pod	133651	0644	edit dl rm
perl5161delta.pod	6142	0644	edit dl rm
perl5162delta.pod	3594	0644	edit dl rm
perl5163delta.pod	4085	0644	edit dl rm
perl5180delta.pod	119429	0644	edit dl rm
perl5181delta.pod	6597	0644	edit dl rm
perl5182delta.pod	5335	0644	edit dl rm
perl5184delta.pod	4642	0644	edit dl rm
perl5200delta.pod	115698	0644	edit dl rm
perl5201delta.pod	10899	0644	edit dl rm
perl5202delta.pod	12509	0644	edit dl rm
perl5203delta.pod	9392	0644	edit dl rm
perl5220delta.pod	130963	0644	edit dl rm
perl5221delta.pod	10767	0644	edit dl rm
perl5222delta.pod	12629	0644	edit dl rm
perl5223delta.pod	8456	0644	edit dl rm
perl5224delta.pod	4460	0644	edit dl rm
perl5240delta.pod	64923	0644	edit dl rm
perl5241delta.pod	8215	0644	edit dl rm
perl5242delta.pod	4113	0644	edit dl rm
perl5243delta.pod	11428	0644	edit dl rm
perl5244delta.pod	4510	0644	edit dl rm
perl5260delta.pod	101835	0644	edit dl rm
perl5261delta.pod	7927	0644	edit dl rm
perl5262delta.pod	7880	0644	edit dl rm
perl5263delta.pod	7067	0644	edit dl rm
perl5280delta.pod	72113	0644	edit dl rm
perl5281delta.pod	4639	0644	edit dl rm
perl5282delta.pod	6200	0644	edit dl rm
perl5283delta.pod	5111	0644	edit dl rm
perl5300delta.pod	41281	0644	edit dl rm
perl5301delta.pod	5730	0644	edit dl rm
perl5302delta.pod	4682	0644	edit dl rm
perl5303delta.pod	4980	0644	edit dl rm
perl5320delta.pod	54601	0644	edit dl rm
perl5321delta.pod	7003	0644	edit dl rm
perlaix.pod	20438	0644	edit dl rm
perlamiga.pod	5749	0644	edit dl rm
perlandroid.pod	8222	0644	edit dl rm
perlapi.pod	493106	0644	edit dl rm
perlapio.pod	21336	0644	edit dl rm
perlartistic.pod	7010	0644	edit dl rm
perlbook.pod	8386	0644	edit dl rm
perlboot.pod	294	0644	edit dl rm
perlbot.pod	304	0644	edit dl rm
perlbs2000.pod	7994	0644	edit dl rm
perlcall.pod	56738	0644	edit dl rm
perlcheat.pod	4480	0644	edit dl rm
perlclib.pod	9607	0644	edit dl rm
perlcn.pod	4763	0644	edit dl rm
perlcommunity.pod	6983	0644	edit dl rm
perlcygwin.pod	27202	0644	edit dl rm
perldata.pod	49782	0644	edit dl rm
perldbmfilter.pod	4981	0644	edit dl rm
perldebguts.pod	42331	0644	edit dl rm
perldebtut.pod	22152	0644	edit dl rm
perldebug.pod	39383	0644	edit dl rm
perldelta.pod	7003	0644	edit dl rm
perldeprecation.pod	20825	0644	edit dl rm
perldiag.pod	296986	0644	edit dl rm
perldos.pod	10522	0644	edit dl rm
perldsc.pod	25614	0644	edit dl rm
perldtrace.pod	7959	0644	edit dl rm
perlebcdic.pod	84345	0644	edit dl rm
perlembed.pod	37569	0644	edit dl rm
perlexperiment.pod	7234	0644	edit dl rm
perlfork.pod	13355	0644	edit dl rm
perlform.pod	16608	0644	edit dl rm
perlfreebsd.pod	1623	0644	edit dl rm
perlfunc.pod	403777	0644	edit dl rm
perlgit.pod	29591	0644	edit dl rm
perlgov.pod	14481	0644	edit dl rm
perlgpl.pod	13815	0644	edit dl rm
perlguts.pod	162103	0644	edit dl rm
perlhack.pod	43157	0644	edit dl rm
perlhacktips.pod	57692	0644	edit dl rm
perlhacktut.pod	6153	0644	edit dl rm
perlhaiku.pod	1508	0644	edit dl rm
perlhist.pod	56164	0644	edit dl rm
perlhpux.pod	30609	0644	edit dl rm
perlhurd.pod	1994	0644	edit dl rm
perlintern.pod	83565	0644	edit dl rm
perlinterp.pod	33715	0644	edit dl rm
perlintro.pod	22135	0644	edit dl rm
perliol.pod	34804	0644	edit dl rm
perlipc.pod	71529	0644	edit dl rm
perlirix.pod	4415	0644	edit dl rm
perljp.pod	8431	0644	edit dl rm
perlko.pod	12208	0644	edit dl rm
perllexwarn.pod	355	0644	edit dl rm
perllinux.pod	2007	0644	edit dl rm
perllocale.pod	74112	0644	edit dl rm
perllol.pod	9580	0644	edit dl rm
perlmacos.pod	998	0644	edit dl rm
perlmacosx.pod	12124	0644	edit dl rm
perlmod.pod	26197	0644	edit dl rm
perlmodinstall.pod	10261	0644	edit dl rm
perlmodlib.pod	76348	0644	edit dl rm
perlmodstyle.pod	22588	0644	edit dl rm
perlmroapi.pod	3280	0644	edit dl rm
perlnetware.pod	6648	0644	edit dl rm
perlnewmod.pod	11037	0644	edit dl rm
perlnumber.pod	8353	0644	edit dl rm
perlobj.pod	35717	0644	edit dl rm
perlootut.pod	26757	0644	edit dl rm
perlop.pod	148888	0644	edit dl rm
perlopenbsd.pod	1224	0644	edit dl rm
perlopentut.pod	15223	0644	edit dl rm
perlos2.pod	93348	0644	edit dl rm
perlos390.pod	16527	0644	edit dl rm
perlos400.pod	4765	0644	edit dl rm
perlpacktut.pod	51370	0644	edit dl rm
perlperf.pod	49881	0644	edit dl rm
perlplan9.pod	5125	0644	edit dl rm
perlpod.pod	23076	0644	edit dl rm
perlpodspec.pod	68628	0644	edit dl rm
perlpolicy.pod	26562	0644	edit dl rm
perlport.pod	88693	0644	edit dl rm
perlpragma.pod	5176	0644	edit dl rm
perlqnx.pod	6673	0644	edit dl rm
perlre.pod	130817	0644	edit dl rm
perlreapi.pod	30245	0644	edit dl rm
perlrebackslash.pod	32285	0644	edit dl rm
perlrecharclass.pod	49707	0644	edit dl rm
perlref.pod	35432	0644	edit dl rm
perlreftut.pod	18826	0644	edit dl rm
perlreguts.pod	39301	0644	edit dl rm
perlrepository.pod	509	0644	edit dl rm
perlrequick.pod	19141	0644	edit dl rm
perlreref.pod	15590	0644	edit dl rm
perlretut.pod	122527	0644	edit dl rm
perlriscos.pod	1529	0644	edit dl rm
perlrun.pod	55980	0644	edit dl rm
perlsec.pod	27601	0644	edit dl rm
perlsecpolicy.pod	19450	0644	edit dl rm
perlsolaris.pod	29843	0644	edit dl rm
perlsource.pod	7132	0644	edit dl rm
perlstyle.pod	8734	0644	edit dl rm
perlsub.pod	74405	0644	edit dl rm
perlsymbian.pod	15344	0644	edit dl rm
perlsyn.pod	45138	0644	edit dl rm
perlsynology.pod	7960	0644	edit dl rm
perlthrtut.pod	46522	0644	edit dl rm
perltie.pod	39314	0644	edit dl rm
perltoc.pod	701800	0644	edit dl rm
perltodo.pod	372	0644	edit dl rm
perltooc.pod	294	0644	edit dl rm
perltoot.pod	294	0644	edit dl rm
perltrap.pod	10623	0644	edit dl rm
perltru64.pod	8492	0644	edit dl rm
perltw.pod	4463	0644	edit dl rm
perlunicode.pod	91353	0644	edit dl rm
perlunicook.pod	25658	0644	edit dl rm
perlunifaq.pod	13644	0644	edit dl rm
perluniintro.pod	38647	0644	edit dl rm
perluniprops.pod	441614	0644	edit dl rm
perlunitut.pod	7951	0644	edit dl rm
perlutil.pod	7291	0644	edit dl rm
perlvar.pod	82577	0644	edit dl rm
perlvms.pod	50823	0644	edit dl rm
perlvos.pod	3843	0644	edit dl rm
perlwin32.pod	40317	0644	edit dl rm

Edit: /usr/share/perl5/pod/perltrap.pod (10623B)

=head1 NAME

perltrap - Perl traps for the unwary

=head1 DESCRIPTION

The biggest trap of all is forgetting to C<use warnings> or use the B<-w>
switch; see L<warnings> and L<perlrun/-w>. The second biggest trap is not
making your entire program runnable under C<use strict>.  The third biggest
trap is not reading the list of changes in this version of Perl; see
L<perldelta>.

=head2 Awk Traps

Accustomed B<awk> users should take special note of the following:

=over 4

=item *

A Perl program executes only once, not once for each input line.  You can
do an implicit loop with C<-n> or C<-p>.

=item *

The English module, loaded via

use English;

allows you to refer to special variables (like C<$/>) with names (like
$RS), as though they were in B<awk>; see L<perlvar> for details.

=item *

Semicolons are required after all simple statements in Perl (except
at the end of a block).  Newline is not a statement delimiter.

=item *

Curly brackets are required on C<if>s and C<while>s.

=item *

Variables begin with "$", "@" or "%" in Perl.

=item *

Arrays index from 0.  Likewise string positions in substr() and
index().

=item *

You have to decide whether your array has numeric or string indices.

=item *

Hash values do not spring into existence upon mere reference.

=item *

You have to decide whether you want to use string or numeric
comparisons.

=item *

Reading an input line does not split it for you.  You get to split it
to an array yourself.  And the split() operator has different
arguments than B<awk>'s.

=item *

The current input line is normally in $_, not $0.  It generally does
not have the newline stripped.  ($0 is the name of the program
executed.)  See L<perlvar>.

=item *

$<I<digit>> does not refer to fields--it refers to substrings matched
by the last match pattern.

=item *

The print() statement does not add field and record separators unless
you set C<$,> and C<$\>.  You can set $OFS and $ORS if you're using
the English module.

=item *

You must open your files before you print to them.

=item *

The range operator is "..", not comma.  The comma operator works as in
C.

=item *

The match operator is "=~", not "~".  ("~" is the one's complement
operator, as in C.)

=item *

The exponentiation operator is "**", not "^".  "^" is the XOR
operator, as in C.  (You know, one could get the feeling that B<awk> is
basically incompatible with C.)

=item *

The concatenation operator is ".", not the null string.  (Using the
null string would render C</pat/ /pat/> unparsable, because the third slash
would be interpreted as a division operator--the tokenizer is in fact
slightly context sensitive for operators like "/", "?", and ">".
And in fact, "." itself can be the beginning of a number.)

=item *

The C<next>, C<exit>, and C<continue> keywords work differently.

=item *

The following variables work differently:

Awk	Perl
      ARGC	scalar @ARGV (compare with $#ARGV)
      ARGV[0]	$0
      FILENAME	$ARGV
      FNR	$. - something
      FS	(whatever you like)
      NF	$#Fld, or some such
      NR	$.
      OFMT	$#
      OFS	$,
      ORS	$\
      RLENGTH	length($&)
      RS	$/
      RSTART	length($`)
      SUBSEP	$;

=item *

You cannot set $RS to a pattern, only a string.

=item *

When in doubt, run the B<awk> construct through B<a2p> and see what it
gives you.

=back

=head2 C/C++ Traps

Cerebral C and C++ programmers should take note of the following:

=over 4

=item *

Curly brackets are required on C<if>'s and C<while>'s.

=item *

You must use C<elsif> rather than C<else if>.

=item *

The C<break> and C<continue> keywords from C become in Perl C<last>
and C<next>, respectively.  Unlike in C, these do I<not> work within a
C<do { } while> construct.  See L<perlsyn/"Loop Control">.

=item *

The switch statement is called C<given>/C<when> and only available in
perl 5.10 or newer.  See L<perlsyn/"Switch Statements">.

=item *

Variables begin with "$", "@" or "%" in Perl.

=item *

Comments begin with "#", not "/*" or "//".  Perl may interpret C/C++
comments as division operators, unterminated regular expressions or
the defined-or operator.

=item *

You can't take the address of anything, although a similar operator
in Perl is the backslash, which creates a reference.

=item *

C<ARGV> must be capitalized.  C<$ARGV[0]> is C's C<argv[1]>, and C<argv[0]>
ends up in C<$0>.

=item *

System calls such as link(), unlink(), rename(), etc. return nonzero for
success, not 0. (system(), however, returns zero for success.)

=item *

Signal handlers deal with signal names, not numbers.  Use C<kill -l>
to find their names on your system.

=back

=head2 JavaScript Traps

Judicious JavaScript programmers should take note of the following:

=over 4

=item *

In Perl, binary C<+> is always addition.  C<$string1 + $string2> converts
both strings to numbers and then adds them.  To concatenate two strings,
use the C<.> operator.

=item *

The C<+> unary operator doesn't do anything in Perl.  It exists to avoid
syntactic ambiguities.

=item *

Unlike C<for...in>, Perl's C<for> (also spelled C<foreach>) does not allow
the left-hand side to be an arbitrary expression.  It must be a variable:

for my $variable (keys %hash) {
	...
   }

Furthermore, don't forget the C<keys> in there, as
C<foreach my $kv (%hash) {}> iterates over the keys and values, and is
generally not useful ($kv would be a key, then a value, and so on).

=item *

To iterate over the indices of an array, use C<foreach my $i (0 .. $#array)
{}>.  C<foreach my $v (@array) {}> iterates over the values.

=item *

Perl requires braces following C<if>, C<while>, C<foreach>, etc.

=item *

In Perl, C<else if> is spelled C<elsif>.

=item *

C<? :> has higher precedence than assignment.  In JavaScript, one can
write:

condition ? do_something() : variable = 3

and the variable is only assigned if the condition is false.  In Perl, you
need parentheses:

$condition ? do_something() : ($variable = 3);

Or just use C<if>.

=item *

Perl requires semicolons to separate statements.

=item *

Variables declared with C<my> only affect code I<after> the declaration.
You cannot write C<$x = 1; my $x;> and expect the first assignment to
affect the same variable.  It will instead assign to an C<$x> declared
previously in an outer scope, or to a global variable.

Note also that the variable is not visible until the following
I<statement>.  This means that in C<my $x = 1 + $x> the second $x refers
to one declared previously.

=item *

C<my> variables are scoped to the current block, not to the current
function.  If you write C<{my $x;} $x;>, the second C<$x> does not refer to
the one declared inside the block.

=item *

An object's members cannot be made accessible as variables.  The closest
Perl equivalent to C<with(object) { method() }> is C<for>, which can alias
C<$_> to the object:

for ($object) {
	$_->method;
    }

=item *

The object or class on which a method is called is passed as one of the
method's arguments, not as a separate C<this> value.

=back

=head2 Sed Traps

Seasoned B<sed> programmers should take note of the following:

=over 4

=item *

A Perl program executes only once, not once for each input line.  You can
do an implicit loop with C<-n> or C<-p>.

=item *

Backreferences in substitutions use "$" rather than "\".

=item *

The pattern matching metacharacters "(", ")", and "|" do not have backslashes
in front.

=item *

The range operator is C<...>, rather than comma.

=back

=head2 Shell Traps

Sharp shell programmers should take note of the following:

=over 4

=item *

The backtick operator does variable interpolation without regard to
the presence of single quotes in the command.

=item *

The backtick operator does no translation of the return value, unlike B<csh>.

=item *

Shells (especially B<csh>) do several levels of substitution on each
command line.  Perl does substitution in only certain constructs
such as double quotes, backticks, angle brackets, and search patterns.

=item *

Shells interpret scripts a little bit at a time.  Perl compiles the
entire program before executing it (except for C<BEGIN> blocks, which
execute at compile time).

=item *

The arguments are available via @ARGV, not $1, $2, etc.

=item *

The environment is not automatically made available as separate scalar
variables.

=item *

The shell's C<test> uses "=", "!=", "<" etc for string comparisons and "-eq",
"-ne", "-lt" etc for numeric comparisons. This is the reverse of Perl, which
uses C<eq>, C<ne>, C<lt> for string comparisons, and C<==>, C<!=> C<< < >> etc
for numeric comparisons.

=back

=head2 Perl Traps

Practicing Perl Programmers should take note of the following:

=over 4

=item *

Remember that many operations behave differently in a list
context than they do in a scalar one.  See L<perldata> for details.

=item *

Avoid barewords if you can, especially all lowercase ones.
You can't tell by just looking at it whether a bareword is
a function or a string.  By using quotes on strings and
parentheses on function calls, you won't ever get them confused.

=item *

You cannot discern from mere inspection which builtins
are unary operators (like chop() and chdir())
and which are list operators (like print() and unlink()).
(Unless prototyped, user-defined subroutines can B<only> be list
operators, never unary ones.)  See L<perlop> and L<perlsub>.

=item *

People have a hard time remembering that some functions
default to $_, or @ARGV, or whatever, but that others which
you might expect to do not.

=item *

The <FH> construct is not the name of the filehandle, it is a readline
operation on that handle.  The data read is assigned to $_ only if the
file read is the sole condition in a while loop:

while (<FH>)      { }
    while (defined($_ = <FH>)) { }..
    <FH>;  # data discarded!

=item *

Remember not to use C<=> when you need C<=~>;
these two constructs are quite different:

$x =  /foo/;
    $x =~ /foo/;

=item *

The C<do {}> construct isn't a real loop that you can use
loop control on.

=item *

Use C<my()> for local variables whenever you can get away with
it (but see L<perlform> for where you can't).
Using C<local()> actually gives a local value to a global
variable, which leaves you open to unforeseen side-effects
of dynamic scoping.

=item *

If you localize an exported variable in a module, its exported value will
not change.  The local name becomes an alias to a new value but the
external name is still an alias for the original.

=back

As always, if any of these are ever officially declared as bugs,
they'll be fixed and removed.

=head1 NAME perltrap - Perl traps for the unwary =head1 DESCRIPTION The biggest trap of all is forgetting to C or use the B<-w> switch; see L and L. The second biggest trap is not making your entire program runnable under C. The third biggest trap is not reading the list of changes in this version of Perl; see L. =head2 Awk Traps Accustomed B users should take special note of the following: =over 4 =item * A Perl program executes only once, not once for each input line. You can do an implicit loop with C<-n> or C<-p>. =item * The English module, loaded via use English; allows you to refer to special variables (like C<$/>) with names (like $RS), as though they were in B; see L for details. =item * Semicolons are required after all simple statements in Perl (except at the end of a block). Newline is not a statement delimiter. =item * Curly brackets are required on Cs and Cs. =item * Variables begin with "$", "@" or "%" in Perl. =item * Arrays index from 0. Likewise string positions in substr() and index(). =item * You have to decide whether your array has numeric or string indices. =item * Hash values do not spring into existence upon mere reference. =item * You have to decide whether you want to use string or numeric comparisons. =item * Reading an input line does not split it for you. You get to split it to an array yourself. And the split() operator has different arguments than B's. =item * The current input line is normally in $_, not $0. It generally does not have the newline stripped. ($0 is the name of the program executed.) See L. =item * $> does not refer to fields--it refers to substrings matched by the last match pattern. =item * The print() statement does not add field and record separators unless you set C<$,> and C<$\>. You can set $OFS and $ORS if you're using the English module. =item * You must open your files before you print to them. =item * The range operator is "..", not comma. The comma operator works as in C. =item * The match operator is "=~", not "~". ("~" is the one's complement operator, as in C.) =item * The exponentiation operator is "**", not "^". "^" is the XOR operator, as in C. (You know, one could get the feeling that B is basically incompatible with C.) =item * The concatenation operator is ".", not the null string. (Using the null string would render C unparsable, because the third slash would be interpreted as a division operator--the tokenizer is in fact slightly context sensitive for operators like "/", "?", and ">". And in fact, "." itself can be the beginning of a number.) =item * The C, C, and C keywords work differently. =item * The following variables work differently: Awk Perl ARGC scalar @ARGV (compare with $#ARGV) ARGV[0] $0 FILENAME $ARGV FNR $. - something FS (whatever you like) NF $#Fld, or some such NR $. OFMT $# OFS $, ORS $\ RLENGTH length($&) RS $/ RSTART length($`) SUBSEP $; =item * You cannot set $RS to a pattern, only a string. =item * When in doubt, run the B construct through B and see what it gives you. =back =head2 C/C++ Traps Cerebral C and C++ programmers should take note of the following: =over 4 =item * Curly brackets are required on C's and C's. =item * You must use C rather than C. =item * The C and C keywords from C become in Perl C and C, respectively. Unlike in C, these do I work within a C construct. See L. =item * The switch statement is called C/C and only available in perl 5.10 or newer. See L. =item * Variables begin with "$", "@" or "%" in Perl. =item * Comments begin with "#", not "/*" or "//". Perl may interpret C/C++ comments as division operators, unterminated regular expressions or the defined-or operator. =item * You can't take the address of anything, although a similar operator in Perl is the backslash, which creates a reference. =item * C must be capitalized. C<$ARGV[0]> is C's C, and C ends up in C<$0>. =item * System calls such as link(), unlink(), rename(), etc. return nonzero for success, not 0. (system(), however, returns zero for success.) =item * Signal handlers deal with signal names, not numbers. Use C to find their names on your system. =back =head2 JavaScript Traps Judicious JavaScript programmers should take note of the following: =over 4 =item * In Perl, binary C<+> is always addition. C<$string1 + $string2> converts both strings to numbers and then adds them. To concatenate two strings, use the C<.> operator. =item * The C<+> unary operator doesn't do anything in Perl. It exists to avoid syntactic ambiguities. =item * Unlike C, Perl's C (also spelled C) does not allow the left-hand side to be an arbitrary expression. It must be a variable: for my $variable (keys %hash) { ... } Furthermore, don't forget the C in there, as C iterates over the keys and values, and is generally not useful ($kv would be a key, then a value, and so on). =item * To iterate over the indices of an array, use C. C iterates over the values. =item * Perl requires braces following C, C, C, etc. =item * In Perl, C is spelled C. =item * C has higher precedence than assignment. In JavaScript, one can write: condition ? do_something() : variable = 3 and the variable is only assigned if the condition is false. In Perl, you need parentheses: $condition ? do_something() : ($variable = 3); Or just use C. =item * Perl requires semicolons to separate statements. =item * Variables declared with C only affect code I the declaration. You cannot write C<$x = 1; my $x;> and expect the first assignment to affect the same variable. It will instead assign to an C<$x> declared previously in an outer scope, or to a global variable. Note also that the variable is not visible until the following I. This means that in C the second $x refers to one declared previously. =item * C variables are scoped to the current block, not to the current function. If you write C<{my $x;} $x;>, the second C<$x> does not refer to the one declared inside the block. =item * An object's members cannot be made accessible as variables. The closest Perl equivalent to C is C, which can alias C<$_> to the object: for ($object) { $_->method; } =item * The object or class on which a method is called is passed as one of the method's arguments, not as a separate C value. =back =head2 Sed Traps Seasoned B programmers should take note of the following: =over 4 =item * A Perl program executes only once, not once for each input line. You can do an implicit loop with C<-n> or C<-p>. =item * Backreferences in substitutions use "$" rather than "\". =item * The pattern matching metacharacters "(", ")", and "|" do not have backslashes in front. =item * The range operator is C<...>, rather than comma. =back =head2 Shell Traps Sharp shell programmers should take note of the following: =over 4 =item * The backtick operator does variable interpolation without regard to the presence of single quotes in the command. =item * The backtick operator does no translation of the return value, unlike B. =item * Shells (especially B) do several levels of substitution on each command line. Perl does substitution in only certain constructs such as double quotes, backticks, angle brackets, and search patterns. =item * Shells interpret scripts a little bit at a time. Perl compiles the entire program before executing it (except for C blocks, which execute at compile time). =item * The arguments are available via @ARGV, not $1, $2, etc. =item * The environment is not automatically made available as separate scalar variables. =item * The shell's C uses "=", "!=", "<" etc for string comparisons and "-eq", "-ne", "-lt" etc for numeric comparisons. This is the reverse of Perl, which uses C, C, C for string comparisons, and C<==>, C C<< < >> etc for numeric comparisons. =back =head2 Perl Traps Practicing Perl Programmers should take note of the following: =over 4 =item * Remember that many operations behave differently in a list context than they do in a scalar one. See L for details. =item * Avoid barewords if you can, especially all lowercase ones. You can't tell by just looking at it whether a bareword is a function or a string. By using quotes on strings and parentheses on function calls, you won't ever get them confused. =item * You cannot discern from mere inspection which builtins are unary operators (like chop() and chdir()) and which are list operators (like print() and unlink()). (Unless prototyped, user-defined subroutines can B be list operators, never unary ones.) See L and L. =item * People have a hard time remembering that some functions default to $_, or @ARGV, or whatever, but that others which you might expect to do not. =item * The construct is not the name of the filehandle, it is a readline operation on that handle. The data read is assigned to $_ only if the file read is the sole condition in a while loop: while () { } while (defined($_ = )) { }.. ; # data discarded! =item * Remember not to use C<=> when you need C<=~>; these two constructs are quite different: $x = /foo/; $x =~ /foo/; =item * The C construct isn't a real loop that you can use loop control on. =item * Use C for local variables whenever you can get away with it (but see L for where you can't). Using C actually gives a local value to a global variable, which leaves you open to unforeseen side-effects of dynamic scoping. =item * If you localize an exported variable in a module, its exported value will not change. The local name becomes an alias to a new value but the external name is still an alias for the original. =back As always, if any of these are ever officially declared as bugs, they'll be fixed and removed.