a2p
accept
access
acct
addftinfo
addr2line
adjtime
afmtodit
after
aio_cancel
aio_error
aio_read
aio_return
aio_suspend
aio_waitcomplete
aio_write
alias
aliases
alloc
anvil
append
apply
apropos
ar
array
as
asa
asn1parse
at
atq
atrm
attemptckalloc
attemptckrealloc
authlib
authtest
autopoint
awk
b64decode
b64encode
basename
batch
bc
bdes
bell
bg
bgerror
biff
big5
binary
bind
bindkey
bindtags
bindtextdomain
bio
bitmap
blowfish
bn
bootparams
bootptab
bounce
brandelf
break
breaksw
brk
bsdiff
bsdtar
bsnmpd
bspatch
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buffer
builtin
builtins
bunzip2
button
byacc
bzcat
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bzip2
c2ph
c89
c99
ca
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calendar
canvas
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case
cat
catch
catman
cc
cd
cdcontrol
chdir
checkbutton
checknr
chflags
chfn
chgrp
chio
chkey
chmod
chown
chpass
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chsh
ci
ciphers
ckalloc
ckdist
ckfree
ckrealloc
cksum
cleanup
clear
clipboard
clock
clock_getres
clock_gettime
clock_settime
close
cmp
co
col
colcrt
colldef
colors
colrm
column
comm
command
compile_et
complete
compress
concat
config
connect
console
continue
core
courierlogger
couriertcpd
cp
cpan
cpio
cpp
creat
crl
crontab
crunchgen
crunchide
crypt
crypto
csh
csplit
ctags
ctm
ctm_dequeue
ctm_rmail
ctm_smail
cu
cursor
cursors
cut
cvs
date
dbiprof
dbiproxy
dc
dcgettext
dcngettext
dd
dde
default
defer
deliverquota
des
destroy
devfs
df
dgettext
dgst
dh
dhparam
dialog
diff
diff3
dig
dir
dirent
dirname
dirs
discard
disktab
dngettext
do
domainname
done
dprofpp
dsa
dsaparam
dtmfdecode
du
dup
dup2
eaccess
ec
ecdsa
echo
echotc
ecparam
ed
edit
editrc
ee
egrep
elf
elfdump
elif
else
enc
enc2xs
encoding
end
endif
endsw
engine
enigma
entry
env
envsubst
eof
eqn
err
errno
error
errstr
esac
ethers
euc
eui64
eval
event
evp
ex
exec
execve
exit
expand
export
exports
expr
extattr
extattr_delete_fd
extattr_delete_file
extattr_get_fd
extattr_get_file
extattr_set_fd
extattr_set_file
f77
false
famm
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fbtab
fc
fchdir
fchflags
fchmod
fchown
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fconfigure
fcopy
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fdformat
fdread
fdwrite
fetch
fg
fgrep
fhopen
fhstat
fhstatfs
fi
file
file2c
fileevent
filename
filetest
find
find2perl
finger
flex
flock
flush
fmt
focus
fold
font
fontedit
for
foreach
fork
format
forward
fpathconf
frame
from
fs
fstab
fstat
fstatfs
fsync
ftp
ftpchroot
ftpusers
ftruncate
futimes
g711conv
gb2312
gb18030
gbk
gcc
gcore
gcov
gdb
gencat
gendsa
genrsa
gensnmptree
getconf
getdents
getdirentries
getdtablesize
getegid
geteuid
getfacl
getfh
getfsstat
getgid
getgroups
getitimer
getlogin
getopt
getopts
getpeername
getpgid
getpgrp
getpid
getppid
getpriority
getresgid
getresuid
getrlimit
getrusage
gets
getsid
getsockname
getsockopt
gettext
gettextize
gettimeofday
gettytab
getuid
glob
global
gmake
goto
gperf
gprof
grab
grep
grid
grn
grodvi
groff
groff_font
groff_out
groff_tmac
grog
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grolj4
grops
grotty
group
groups
gunzip
gzcat
gzexe
gzip
h2ph
h2xs
hash
hashstat
hd
head
help2man
hesinfo
hexdump
history
host
hostname
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hosts_access
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hpftodit
http
hup
i386_get_ioperm
i386_get_ldt
i386_set_ioperm
i386_set_ldt
i386_vm86
iconv
id
ident
idprio
if
ifnames253
ifnames259
image
imapd
incr
indent
indxbib
info
infokey
inode
install
instmodsh
interp
intro
introduction
ioctl
ipcrm
ipcs
ipf
ipftest
ipnat
ippool
ipresend
issetugid
jail
jail_attach
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jobs
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jot
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lam
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limit
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link
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list
listbox
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ln
load
loadfont
local
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locate
lock
lockf
log
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lp
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objcopy
objdump
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ocsp
od
onintr
open
openssl
opieaccess
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option
options
oqmgr
pack
package
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pathchk
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pawd
pax
pbm
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pcrepartial
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pcreperform
pcreposix
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perl
perl56delta
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zcat
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zdiff
zegrep
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_exit
__syscall
 
FreeBSD/Linux/UNIX General Commands Manual
Hypertext Man Pages
perlstyle
 
PERLSTYLE(1)	       Perl Programmers Reference Guide 	  PERLSTYLE(1)



NAME
       perlstyle - Perl style guide

DESCRIPTION
       Each programmer will, of course, have his or her own preferences in
       regards to formatting, but there are some general guidelines that will
       make your programs easier to read, understand, and maintain.

       The most important thing is to run your programs under the -w flag at
       all times.  You may turn it off explicitly for particular portions of
       code via the "no warnings" pragma or the $^W variable if you must.  You
       should also always run under "use strict" or know the reason why not.
       The "use sigtrap" and even "use diagnostics" pragmas may also prove
       useful.

       Regarding aesthetics of code lay out, about the only thing Larry cares
       strongly about is that the closing curly bracket of a multi-line BLOCK
       should line up with the keyword that started the construct.  Beyond
       that, he has other preferences that aren't so strong:

       o   4-column indent.

       o   Opening curly on same line as keyword, if possible, otherwise line
	   up.

       o   Space before the opening curly of a multi-line BLOCK.

       o   One-line BLOCK may be put on one line, including curlies.

       o   No space before the semicolon.

       o   Semicolon omitted in "short" one-line BLOCK.

       o   Space around most operators.

       o   Space around a "complex" subscript (inside brackets).

       o   Blank lines between chunks that do different things.

       o   Uncuddled elses.

       o   No space between function name and its opening parenthesis.

       o   Space after each comma.

       o   Long lines broken after an operator (except "and" and "or").

       o   Space after last parenthesis matching on current line.

       o   Line up corresponding items vertically.

       o   Omit redundant punctuation as long as clarity doesn't suffer.

       Larry has his reasons for each of these things, but he doesn't claim
       that everyone else's mind works the same as his does.

       Here are some other more substantive style issues to think about:

       o   Just because you CAN do something a particular way doesn't mean
	   that you SHOULD do it that way.  Perl is designed to give you sev-
	   eral ways to do anything, so consider picking the most readable
	   one.  For instance

	       open(FOO,$foo) || die "Can't open $foo: $!";

	   is better than

	       die "Can't open $foo: $!" unless open(FOO,$foo);

	   because the second way hides the main point of the statement in a
	   modifier.  On the other hand

	       print "Starting analysis\n" if $verbose;

	   is better than

	       $verbose && print "Starting analysis\n";

	   because the main point isn't whether the user typed -v or not.

	   Similarly, just because an operator lets you assume default argu-
	   ments doesn't mean that you have to make use of the defaults.  The
	   defaults are there for lazy systems programmers writing one-shot
	   programs.  If you want your program to be readable, consider sup-
	   plying the argument.

	   Along the same lines, just because you CAN omit parentheses in many
	   places doesn't mean that you ought to:

	       return print reverse sort num values %array;
	       return print(reverse(sort num (values(%array))));

	   When in doubt, parenthesize.  At the very least it will let some
	   poor schmuck bounce on the % key in vi.

	   Even if you aren't in doubt, consider the mental welfare of the
	   person who has to maintain the code after you, and who will proba-
	   bly put parentheses in the wrong place.

       o   Don't go through silly contortions to exit a loop at the top or the
	   bottom, when Perl provides the "last" operator so you can exit in
	   the middle.	Just "outdent" it a little to make it more visible:

	       LINE:
		   for (;;) {
		       statements;
		     last LINE if $foo;
		       next LINE if /^#/;
		       statements;
		   }

       o   Don't be afraid to use loop labels--they're there to enhance read-
	   ability as well as to allow multilevel loop breaks.	See the previ-
	   ous example.

       o   Avoid using "grep()" (or "map()") or `backticks` in a void context,
	   that is, when you just throw away their return values.  Those func-
	   tions all have return values, so use them.  Otherwise use a "fore-
	   ach()" loop or the "system()" function instead.

       o   For portability, when using features that may not be implemented on
	   every machine, test the construct in an eval to see if it fails.
	   If you know what version or patchlevel a particular feature was
	   implemented, you can test $] ($PERL_VERSION in "English") to see if
	   it will be there.  The "Config" module will also let you interro-
	   gate values determined by the Configure program when Perl was
	   installed.

       o   Choose mnemonic identifiers.  If you can't remember what mnemonic
	   means, you've got a problem.

       o   While short identifiers like $gotit are probably ok, use under-
	   scores to separate words in longer identifiers.  It is generally
	   easier to read $var_names_like_this than $VarNamesLikeThis, espe-
	   cially for non-native speakers of English. It's also a simple rule
	   that works consistently with "VAR_NAMES_LIKE_THIS".

	   Package names are sometimes an exception to this rule.  Perl infor-
	   mally reserves lowercase module names for "pragma" modules like
	   "integer" and "strict".  Other modules should begin with a capital
	   letter and use mixed case, but probably without underscores due to
	   limitations in primitive file systems' representations of module
	   names as files that must fit into a few sparse bytes.

       o   You may find it helpful to use letter case to indicate the scope or
	   nature of a variable. For example:

	       $ALL_CAPS_HERE	constants only (beware clashes with perl vars!)
	       $Some_Caps_Here	package-wide global/static
	       $no_caps_here	function scope my() or local() variables

	   Function and method names seem to work best as all lowercase.
	   E.g., "$obj->as_string()".

	   You can use a leading underscore to indicate that a variable or
	   function should not be used outside the package that defined it.

       o   If you have a really hairy regular expression, use the "/x" modi-
	   fier and put in some whitespace to make it look a little less like
	   line noise.	Don't use slash as a delimiter when your regexp has
	   slashes or backslashes.

       o   Use the new "and" and "or" operators to avoid having to parenthe-
	   size list operators so much, and to reduce the incidence of punctu-
	   ation operators like "&&" and "||".	Call your subroutines as if
	   they were functions or list operators to avoid excessive ampersands
	   and parentheses.

       o   Use here documents instead of repeated "print()" statements.

       o   Line up corresponding things vertically, especially if it'd be too
	   long to fit on one line anyway.

	       $IDX = $ST_MTIME;
	       $IDX = $ST_ATIME       if $opt_u;
	       $IDX = $ST_CTIME       if $opt_c;
	       $IDX = $ST_SIZE	      if $opt_s;

	       mkdir $tmpdir, 0700 or die "can't mkdir $tmpdir: $!";
	       chdir($tmpdir)	   or die "can't chdir $tmpdir: $!";
	       mkdir 'tmp',   0777 or die "can't mkdir $tmpdir/tmp: $!";

       o   Always check the return codes of system calls.  Good error messages
	   should go to "STDERR", include which program caused the problem,
	   what the failed system call and arguments were, and (VERY IMPOR-
	   TANT) should contain the standard system error message for what
	   went wrong.	Here's a simple but sufficient example:

	       opendir(D, $dir)     or die "can't opendir $dir: $!";

       o   Line up your transliterations when it makes sense:

	       tr [abc]
		  [xyz];

       o   Think about reusability.  Why waste brainpower on a one-shot when
	   you might want to do something like it again?  Consider generaliz-
	   ing your code.  Consider writing a module or object class.  Con-
	   sider making your code run cleanly with "use strict" and "use warn-
	   ings" (or -w) in effect.  Consider giving away your code.  Consider
	   changing your whole world view.  Consider... oh, never mind.

       o   Try to document your code and use Pod formatting in a consistent
	   way. Here are commonly expected conventions:

	   o   use "C<>" for function, variable and module names (and more
	       generally anything that can be considered part of code, like
	       filehandles or specific values). Note that function names are
	       considered more readable with parentheses after their name,
	       that is "function()".

	   o   use "B<>" for commands names like cat or grep.

	   o   use "F<>" or "C<>" for file names. "F<>" should be the only Pod
	       code for file names, but as most Pod formatters render it as
	       italic, Unix and Windows paths with their slashes and back-
	       slashes may be less readable, and better rendered with "C<>".

       o   Be consistent.

       o   Be nice.



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