perlrun - how to execute the Perl interpreter
perl [ -sTtuUWX ] [ -hv ] [ -V[:configvar] ]
[ -cw ] [ -d[:debugger] ] [ -D[number/list] ]
[ -pna ] [ -Fpattern ] [ -l[octal] ] [
-0[octal/hexadecimal] ]
[ -Idir ] [ -m[-]module ] [ -M[-]'module...' ]
[ -P ] [ -S ] [ -x[dir] ]
[ -i[extension] ]
[ -e 'command' ] [ -- ] [ programfile ] [ argument
]...
[ -C [number/list] ] ]>
The normal way to run a Perl program is by making it
directly executable, or else by passing the name of the
source file as an argument on the command line. (An
interactive Perl environment is also possible--see perldebug
for details on how to do that.) Upon startup, Perl
looks for your program in one of the following places:
1. Specified line by line via -e switches on the command
line.
2. Contained in the file specified by the first filename
on the command line. (Note that systems supporting
the #! notation invoke interpreters this way. See
"Location of Perl".)
3. Passed in implicitly via standard input. This works
only if there are no filename arguments--to pass arguments
to a STDIN-read program you must explicitly
specify a "-" for the program name.
With methods 2 and 3, Perl starts parsing the input file
from the beginning, unless you've specified a -x switch,
in which case it scans for the first line starting with #!
and containing the word "perl", and starts there instead.
This is useful for running a program embedded in a larger
message. (In this case you would indicate the end of the
program using the "__END__" token.)
The #! line is always examined for switches as the line is
being parsed. Thus, if you're on a machine that allows
only one argument with the #! line, or worse, doesn't even
recognize the #! line, you still can get consistent switch
behavior regardless of how Perl was invoked, even if -x
was used to find the beginning of the program.
Because historically some operating systems silently
chopped off kernel interpretation of the #! line after 32
characters, some switches may be passed in on the command
line, and some may not; you could even get a "-" without
its letter, if you're not careful. You probably want to
make sure that all your switches fall either before or
after that 32-character boundary. Most switches don't
actually care if they're processed redundantly, but getting
a "-" instead of a complete switch could cause Perl
to try to execute standard input instead of your program.
And a partial -I switch could also cause odd results.
Some switches do care if they are processed twice, for
instance combinations of -l and -0. Either put all the
switches after the 32-character boundary (if applicable),
or replace the use of -0digits by "BEGIN{ $/ = " digits";
}".
Parsing of the #! switches starts wherever "perl" is mentioned
in the line. The sequences "-*" and "- " are
specifically ignored so that you could, if you were so
inclined, say
#!/bin/sh -- # -*- perl -*- -p
eval 'exec perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
to let Perl see the -p switch.
A similar trick involves the env program, if you have it.
#!/usr/bin/env perl
The examples above use a relative path to the perl interpreter,
getting whatever version is first in the user's
path. If you want a specific version of Perl, say,
perl5.005_57, you should place that directly in the #!
line's path.
If the #! line does not contain the word "perl", the program
named after the #! is executed instead of the Perl
interpreter. This is slightly bizarre, but it helps people
on machines that don't do #!, because they can tell a
program that their SHELL is /usr/bin/perl, and Perl will
then dispatch the program to the correct interpreter for
them.
After locating your program, Perl compiles the entire program
to an internal form. If there are any compilation
errors, execution of the program is not attempted. (This
is unlike the typical shell script, which might run partway
through before finding a syntax error.)
If the program is syntactically correct, it is executed.
If the program runs off the end without hitting an exit()
or die() operator, an implicit exit(0) is provided to
indicate successful completion.
#! and quoting on non-Unix systems
Unix's #! technique can be simulated on other systems:
OS/2
Put
extproc perl -S -your_switches
as the first line in "*.cmd" file (-S due to a bug in
cmd.exe's `extproc' handling).
MS-DOS
Create a batch file to run your program, and codify it
in "ALTERNATE_SHEBANG" (see the dosish.h file in the
source distribution for more information).
Win95/NT
The Win95/NT installation, when using the ActiveState
installer for Perl, will modify the Registry to associate
the .pl extension with the perl interpreter. If
you install Perl by other means (including building
from the sources), you may have to modify the Registry
yourself. Note that this means you can no longer tell
the difference between an executable Perl program and
a Perl library file.
Macintosh
A Macintosh perl program will have the appropriate
Creator and Type, so that double-clicking them will
invoke the perl application.
VMS Put
$ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3'
'p4' 'p5' 'p6' 'p7' 'p8' !
$ exit++ + ++$status != 0 and $exit = $status =
undef;
at the top of your program, where -mysw are any command
line switches you want to pass to Perl. You can
now invoke the program directly, by saying "perl program",
or as a DCL procedure, by saying @program (or
implicitly via DCL$PATH by just using the name of the
program).
This incantation is a bit much to remember, but Perl
will display it for you if you say "perl "-V:startperl"".
Command-interpreters on non-Unix systems have rather different
ideas on quoting than Unix shells. You'll need to
learn the special characters in your command-interpreter
("*", "
pace and these characters to run one-liners (see -e
below).
On some systems, you may have to change single-quotes to
double ones, which you must not do on Unix or Plan 9 systems.
You might also have to change a single % to a %%.
For example:
# Unix
perl -e 'print "Hello world0'
# MS-DOS, etc.
perl -e "print
# Macintosh
print "Hello world0
(then Run "Myscript" or Shift-Command-R)
# VMS
perl -e "print ""Hello world0""
The problem is that none of this is reliable: it depends
on the command and it is entirely possible neither works.
If 4DOS were the command shell, this would probably work
better:
perl -e "print <Ctrl-x>"Hello world0Ctrl-x>""
CMD.EXE in Windows NT slipped a lot of standard Unix functionality
in when nobody was looking, but just try to find
documentation for its quoting rules.
Under the Macintosh, it depends which environment you are
using. The MacPerl shell, or MPW, is much like Unix
shells in its support for several quoting variants, except
that it makes free use of the Macintosh's non-ASCII characters
as control characters.
There is no general solution to all of this. It's just a
mess.
Location of Perl [Toc] [Back]
It may seem obvious to say, but Perl is useful only when
users can easily find it. When possible, it's good for
both /usr/bin/perl and /usr/local/bin/perl to be symlinks
to the actual binary. If that can't be done, system
administrators are strongly encouraged to put (symlinks
to) perl and its accompanying utilities into a directory
typically found along a user's PATH, or in some other
obvious and convenient place.
In this documentation, "#!/usr/bin/perl" on the first line
of the program will stand in for whatever method works on
your system. You are advised to use a specific path if
you care about a specific version.
#!/usr/local/bin/perl5.00554
or if you just want to be running at least version, place
a statement like this at the top of your program:
use 5.005_54;
Command Switches [Toc] [Back]
As with all standard commands, a single-character switch
may be clustered with the following switch, if any.
#!/usr/bin/perl -spi.orig # same as -s -p -i.orig
Switches include:
-0[octal/hexadecimal]
specifies the input record separator ($/) as an octal
or hexadecimal number. If there are no digits, the
null character is the separator. Other switches may
precede or follow the digits. For example, if you
have a version of find which can print filenames terminated
by the null character, you can say this:
find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files
in paragraph mode. The value 0777 will cause Perl to
slurp files whole because there is no legal byte with
that value.
If you want to specify any Unicode character, use the
hexadecimal format: "-0xHHH...", where the "H" are
valid hexadecimal digits. (This means that you cannot
use the "-x" with a directory name that consists
of hexadecimal digits.)
-a turns on autosplit mode when used with a -n or -p.
An implicit split command to the @F array is done as
the first thing inside the implicit while loop produced
by the -n or -p.
perl -ane 'print pop(@F), "0;'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "0;
}
An alternate delimiter may be specified using -F.
-C [number/list]
The "-C" flag controls some Unicode of the Perl Unicode
features.
As of 5.8.1, the "-C" can be followed either by a
number or a list of option letters. The letters,
their numeric values, and effects are as follows;
listing the letters is equal to summing the numbers.
I 1 STDIN is assumed to be in UTF-8
O 2 STDOUT will be in UTF-8
E 4 STDERR will be in UTF-8
S 7 I + O + E
i 8 UTF-8 is the default PerlIO layer for
input streams
o 16 UTF-8 is the default PerlIO layer for
output streams
D 24 i + o
A 32 the @ARGV elements are expected to be
strings encoded in UTF-8
L 64 normally the "IOEioA" are unconditional,
the L makes them conditional on the
locale environment
variables (the LC_ALL, LC_TYPE, and
LANG, in the order
of decreasing precedence) -- if the
variables indicate
UTF-8, then the selected "IOEioA" are
in effect
For example, "-COE" and "-C6" will both turn on
UTF-8-ness on both STDOUT and STDERR. Repeating letters
is just redundant, not cumulative nor toggling.
The "io" options mean that any subsequent open() (or
similar I/O operations) will have the ":utf8" PerlIO
layer implicitly applied to them, in other words,
UTF-8 is expected from any input stream, and UTF-8 is
produced to any output stream. This is just the
default, with explicit layers in open() and with bin-
mode() one can manipulate streams as usual.
"-C" on its own (not followed by any number or option
list), or the empty string "" for the "PERL_UNICODE"
environment variable, has the same effect as "-CSDL".
In other words, the standard I/O handles and the
default "open()" layer are UTF-8-fied but only if the
locale environment variables indicate a UTF-8 locale.
This behaviour follows the implicit (and problematic)
UTF-8 behaviour of Perl 5.8.0.
You can use "-C0" (or "0" for "PERL_UNICODE") to
explicitly disable all the above Unicode features.
The read-only magic variable "${^UNICODE}" reflects
the numeric value of this setting. This is variable
is set during Perl startup and is thereafter
read-only. If you want runtime effects, use the
three-arg open() (see "open" in perlfunc), the twoarg
binmode() (see "binmode" in perlfunc), and the
"open" pragma (see open).
(In Perls earlier than 5.8.1 the "-C" switch was a
Win32-only switch that enabled the use of Unicodeaware
"wide system call" Win32 APIs. This feature
was practically unused, however, and the command line
switch was therefore "recycled".)
-c causes Perl to check the syntax of the program and
then exit without executing it. Actually, it will
execute "BEGIN", "CHECK", and "use" blocks, because
these are considered as occurring outside the execution
of your program. "INIT" and "END" blocks, however,
will be skipped.
-d runs the program under the Perl debugger. See
perldebug.
-d:foo[=bar,baz]
runs the program under the control of a debugging,
profiling, or tracing module installed as Devel::foo.
E.g., -d:DProf executes the program using the
Devel::DProf profiler. As with the -M flag, options
may be passed to the Devel::foo package where they
will be received and interpreted by the
Devel::foo::import routine. The comma-separated list
of options must follow a "=" character. See perldebug.
-Dletters
-Dnumber
sets debugging flags. To watch how it executes your
program, use -Dtls. (This works only if debugging is
compiled into your Perl.) Another nice value is -Dx,
which lists your compiled syntax tree. And -Dr displays
compiled regular expressions; the format of the
output is explained in perldebguts.
As an alternative, specify a number instead of list
of letters (e.g., -D14 is equivalent to -Dtls):
1 p Tokenizing and parsing
2 s Stack snapshots
with v, displays all stacks
4 l Context (loop) stack processing
8 t Trace execution
16 o Method and overloading resolution
32 c String/numeric conversions
64 P Print profiling info, preprocessor command for -P, source file input state
128 m Memory allocation
256 f Format processing
512 r Regular expression parsing and execution
1024 x Syntax tree dump
2048 u Tainting checks
4096 (Obsolete, previously used for LEAKTEST)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
65536 S Thread synchronization
131072 T Tokenising
262144 R Include reference counts of dumped
variables (eg when using -Ds)
524288 J Do not s,t,P-debug (Jump over) opcodes
within package DB
1048576 v Verbose: use in conjunction with other
flags
2097152 C Copy On Write
All these flags require -DDEBUGGING when you compile
the Perl executable (but see Devel::Peek, re which
may change this). See the INSTALL file in the Perl
source distribution for how to do this. This flag is
automatically set if you include -g option when "Configure"
asks you about optimizer/debugger flags.
If you're just trying to get a print out of each line
of Perl code as it executes, the way that "sh -x"
provides for shell scripts, you can't use Perl's -D
switch. Instead do this
# If you have "env" utility
env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2"
perl -dS program
# Bourne shell syntax
$ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl
-dS program
# csh syntax
% (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1
frame=2"; perl -dS program)
See perldebug for details and variations.
-e commandline
may be used to enter one line of program. If -e is
given, Perl will not look for a filename in the argument
list. Multiple -e commands may be given to
build up a multi-line script. Make sure to use semicolons
where you would in a normal program.
-Fpattern
specifies the pattern to split on if -a is also in
effect. The pattern may be surrounded by "//", "",
or '', otherwise it will be put in single quotes.
-h prints a summary of the options.
-i[extension]
specifies that files processed by the "<>" construct
are to be edited in-place. It does this by renaming
the input file, opening the output file by the original
name, and selecting that output file as the
default for print() statements. The extension, if
supplied, is used to modify the name of the old file
to make a backup copy, following these rules:
If no extension is supplied, no backup is made and
the current file is overwritten.
If the extension doesn't contain a "*", then it is
appended to the end of the current filename as a suffix.
If the extension does contain one or more "*"
characters, then each "*" is replaced with the current
filename. In Perl terms, you could think of
this as:
($backup = $extension) =~ s/$file_name/g;
This allows you to add a prefix to the backup file,
instead of (or in addition to) a suffix:
$ perl -pi'orig_*' -e 's/bar/baz/' fileA #
backup to 'orig_fileA'
Or even to place backup copies of the original files
into another directory (provided the directory
already exists):
$ perl -pi'old/*.orig' -e 's/bar/baz/' fileA #
backup to 'old/fileA.orig'
These sets of one-liners are equivalent:
$ perl -pi -e 's/bar/baz/' fileA #
overwrite current file
$ perl -pi'*' -e 's/bar/baz/' fileA #
overwrite current file
$ perl -pi'.orig' -e 's/bar/baz/' fileA #
backup to 'fileA.orig'
$ perl -pi'*.orig' -e 's/bar/baz/' fileA #
backup to 'fileA.orig'
From the shell, saying
$ perl -p -i.orig -e "s/foo/bar/; ... "
is the same as using the program:
#!/usr/bin/perl -pi.orig
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
$extension = '.orig';
LINE: while (<>) {
if ($ARGV ne $oldargv) {
if ($extension !~ /) {
$backup = $ARGV . $extension;
}
else {
($backup = $extension) =~ s/$ARGV/g;
}
rename($ARGV, $backup);
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
}
s/foo/bar/;
}
continue {
print; # this prints to original filename
}
select(STDOUT);
except that the -i form doesn't need to compare $ARGV
to $oldargv to know when the filename has changed.
It does, however, use ARGVOUT for the selected filehandle.
Note that STDOUT is restored as the default
output filehandle after the loop.
As shown above, Perl creates the backup file whether
or not any output is actually changed. So this is
just a fancy way to copy files:
$ perl -p -i'/some/file/path/*' -e 1 file1 file2
file3...
or
$ perl -p -i'.orig' -e 1 file1 file2 file3...
You can use "eof" without parentheses to locate the
end of each input file, in case you want to append to
each file, or reset line numbering (see example in
"eof" in perlfunc).
If, for a given file, Perl is unable to create the
backup file as specified in the extension then it
will skip that file and continue on with the next one
(if it exists).
For a discussion of issues surrounding file permissions
and -i, see "Why does Perl let me delete readonly
files? Why does -i clobber protected files?
Isn't this a bug in Perl?" in perlfaq5.
You cannot use -i to create directories or to strip
extensions from files.
Perl does not expand "~" in filenames, which is good,
since some folks use it for their backup files:
$ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
Finally, the -i switch does not impede execution when
no files are given on the command line. In this
case, no backup is made (the original file cannot, of
course, be determined) and processing proceeds from
STDIN to STDOUT as might be expected.
-Idirectory
Directories specified by -I are prepended to the
search path for modules (@INC), and also tells the C
preprocessor where to search for include files. The
C preprocessor is invoked with -P; by default it
searches /usr/include and /usr/lib/perl.
-l[octnum]
enables automatic line-ending processing. It has two
separate effects. First, it automatically chomps $/
(the input record separator) when used with -n or -p.
Second, it assigns "$
to have the value of octnum so that any print statements
will have that separator added back on. If
octnum is omitted, sets "$
$/. For instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
Note that the assignment "$ = $/" is done when the
switch is processed, so the input record separator
can be different than the output record separator if
the -l switch is followed by a -0 switch:
gnufind / -print0 | perl -ln0e 'print "found $_"
if -p'
This sets "$
null character.
-m[-]module
-M[-]module
-M[-]'module ...'
-[mM][-]module=arg[,arg]...
-mmodule executes "use" module "();" before executing
your program.
-Mmodule executes "use" module ";" before executing
your program. You can use quotes to add extra code
after the module name, e.g., '-Mmodule qw(foo bar)'.
If the first character after the -M or -m is a dash
("-") then the 'use' is replaced with 'no'.
A little builtin syntactic sugar means you can also
say -mmodule=foo,bar or -Mmodule=foo,bar as a shortcut
for '-Mmodule qw(foo bar)'. This avoids the need
to use quotes when importing symbols. The actual
code generated by -Mmodule=foo,bar is "use module
split(/,/,q{foo,bar})". Note that the "=" form
removes the distinction between -m and -M.
-n causes Perl to assume the following loop around your
program, which makes it iterate over filename arguments
somewhat like sed -n or awk:
LINE:
while (<>) {
... # your program goes here
}
Note that the lines are not printed by default. See
-p to have lines printed. If a file named by an
argument cannot be opened for some reason, Perl warns
you about it and moves on to the next file.
Here is an efficient way to delete all files that
haven't been modifed for at least a week:
find . -mtime +7 -print | perl -nle unlink
This is faster than using the -exec switch of find
because you don't have to start a process on every
filename found. It does suffer from the bug of mishandling
newlines in pathnames, which you can fix if
you follow the example under -0.
"BEGIN" and "END" blocks may be used to capture control
before or after the implicit program loop, just
as in awk.
-p causes Perl to assume the following loop around your
program, which makes it iterate over filename arguments
somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!0;
}
If a file named by an argument cannot be opened for
some reason, Perl warns you about it, and moves on to
the next file. Note that the lines are printed automatically.
An error occurring during printing is
treated as fatal. To suppress printing use the -n
switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control
before or after the implicit loop, just as in
awk.
-P NOTE: Use of -P is strongly discouraged because of
its inherent problems, including poor portability.
This option causes your program to be run through the
C preprocessor before compilation by Perl. Because
both comments and cpp directives begin with the #
character, you should avoid starting comments with
any words recognized by the C preprocessor such as
"if", "else", or "define".
If you're considering using "-P", you might also want
to look at the Filter::cpp module from CPAN.
The problems of -P include, but are not limited to:
* The "#!" line is stripped, so any switches
there don't apply.
* A "-P" on a "#!" line doesn't work.
* All lines that begin with (whitespace and)
a "#" but do not look like cpp commands,
are stripped, including anything inside
Perl strings, regular expressions, and
here-docs .
* In some platforms the C preprocessor knows
too much: it knows about the C++ -style
until-end-of-line comments starting with
"//". This will cause problems with common
Perl constructs like
s/foo//;
because after -P this will became illegal
code
s/foo
The workaround is to use some other quoting
separator than "/", like for example "!":
s!foo!!;
* It requires not only a working C preprocessor
but also a working sed. If not on
UNIX, you are probably out of luck on this.
* Script line numbers are not preserved.
* The "-x" does not work with "-P".
-s enables rudimentary switch parsing for switches on
the command line after the program name but before
any filename arguments (or before an argument of --).
This means you can have switches with two leading
dashes (--help). Any switch found there is removed
from @ARGV and sets the corresponding variable in the
Perl program. The following program prints "1" if
the program is invoked with a -xyz switch, and "abc"
if it is invoked with -xyz=abc.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz0 }
Do note that --help creates the variable ${-help},
which is not compliant with "strict refs".
-S makes Perl use the PATH environment variable to
search for the program (unless the name of the program
contains directory separators).
On some platforms, this also makes Perl append suffixes
to the filename while searching for it. For
example, on Win32 platforms, the ".bat" and ".cmd"
suffixes are appended if a lookup for the original
name fails, and if the name does not already end in
one of those suffixes. If your Perl was compiled
with DEBUGGING turned on, using the -Dp switch to
Perl shows how the search progresses.
Typically this is used to emulate #! startup on platforms
that don't support #!. This example works on
many platforms that have a shell compatible with
Bourne shell:
#!/usr/bin/perl
eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
The system ignores the first line and feeds the program
to /bin/sh, which proceeds to try to execute the
Perl program as a shell script. The shell executes
the second line as a normal shell command, and thus
starts up the Perl interpreter. On some systems $0
doesn't always contain the full pathname, so the -S
tells Perl to search for the program if necessary.
After Perl locates the program, it parses the lines
and ignores them because the variable $running_under_some_shell
is never true. If the program
will be interpreted by csh, you will need to replace
"${1+"$@"}" with $*, even though that doesn't understand
embedded spaces (and such) in the argument
list. To start up sh rather than csh, some systems
may have to replace the #! line with a line containing
just a colon, which will be politely ignored by
Perl. Other systems can't control that, and need a
totally devious construct that will work under any of
csh, sh, or Perl, such as the following:
eval '(exit $?0)' && eval 'exec perl -wS $0
${1+"$@"}'
& eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;
If the filename supplied contains directory separators
(i.e., is an absolute or relative pathname), and
if that file is not found, platforms that append file
extensions will do so and try to look for the file
with those extensions added, one by one.
On DOS-like platforms, if the program does not contain
directory separators, it will first be searched
for in the current directory before being searched
for on the PATH. On Unix platforms, the program will
be searched for strictly on the PATH.
-t Like -T, but taint checks will issue warnings rather
than fatal errors. These warnings can be controlled
normally with "no warnings qw(taint)".
NOTE: this is not a substitute for -T. This is meant
only to be used as a temporary development aid while
securing legacy code: for real production code and
for new secure code written from scratch always use
the real -T.
-T forces "taint" checks to be turned on so you can test
them. Ordinarily these checks are done only when
running setuid or setgid. It's a good idea to turn
them on explicitly for programs that run on behalf of
someone else whom you might not necessarily trust,
such as CGI programs or any internet servers you
might write in Perl. See perlsec for details. For
security reasons, this option must be seen by Perl
quite early; usually this means it must appear early
on the command line or in the #! line for systems
which support that construct.
-u This obsolete switch causes Perl to dump core after
compiling your program. You can then in theory take
this core dump and turn it into an executable file by
using the undump program (not supplied). This speeds
startup at the expense of some disk space (which you
can minimize by stripping the executable). (Still, a
"hello world" executable comes out to about 200K on
my machine.) If you want to execute a portion of
your program before dumping, use the dump() operator
instead. Note: availability of undump is platform
specific and may not be available for a specific port
of Perl.
This switch has been superseded in favor of the new
Perl code generator backends to the compiler. See B
and B::Bytecode for details.
-U allows Perl to do unsafe operations. Currently the
only "unsafe" operations are the unlinking of directories
while running as superuser, and running setuid
programs with fatal taint checks turned into warnings.
Note that the -w switch (or the $^W variable)
must be used along with this option to actually gen-
erate the taint-check warnings.
-v prints the version and patchlevel of your perl executable.
-V prints summary of the major perl configuration values
and the current values of @INC.
-V:name
Prints to STDOUT the value of the named configuration
variable(s), with multiples when your query looks
like a regex. For example,
$ perl -V:lib.
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
libc='/lib/libc-2.2.4.so';
$ perl -V:lib.*
libpth='/usr/local/lib /lib /usr/lib';
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
lib_ext='.a';
libc='/lib/libc-2.2.4.so';
libperl='libperl.a';
....
Additionally, extra colons can be used to control
formatting. A trailing colon suppresses the linefeed
and terminator ';', allowing you to embed queries
into shell commands. (mnemonic: PATH separator ':'.)
$ echo "compression-vars: " `perl -V:z.*: ` " are
here !"
compression-vars: zcat='' zip='zip' are here !
A leading colon removes the 'name=' part of the
response, this allows you to map to the name you
need.
$ echo "goodvfork="`./perl -Ilib -V::usevfork`
goodvfork=false;
Leading and trailing colons can be used together if
you need positional parameter values without the
names. Note that in the case below, the PERL_API
params are returned in alphabetical order.
$ echo building_on `perl -V::osname:
-V::PERL_API_.*:` now
building_on 'linux' '5' '1' '9' now
-w prints warnings about dubious constructs, such as
variable names that are mentioned only once and
scalar variables that are used before being set,
redefined subroutines, references to undefined filehandles
or filehandles opened read-only that you are
attempting to write on, values used as a number that
doesn't look like numbers, using an array as though
it were a scalar, if your subroutines recurse more
than 100 deep, and innumerable other things.
This switch really just enables the internal $^W
variable. You can disable or promote into fatal
errors specific warnings using "__WARN__" hooks, as
described in perlvar and "warn" in perlfunc. See
also perldiag and perltrap. A new, fine-grained
warning facility is also available if you want to
manipulate entire classes of warnings; see warnings
or perllexwarn.
-W Enables all warnings regardless of "no warnings" or
$^W. See perllexwarn.
-X Disables all warnings regardless of "use warnings" or
$^W. See perllexwarn.
-x
-x directory
tells Perl that the program is embedded in a larger
chunk of unrelated ASCII text, such as in a mail message.
Leading garbage will be discarded until the
first line that starts with #! and contains the
string "perl". Any meaningful switches on that line
will be applied. If a directory name is specified,
Perl will switch to that directory before running the
program. The -x switch controls only the disposal of
leading garbage. The program must be terminated with
"__END__" if there is trailing garbage to be ignored
(the program can process any or all of the trailing
garbage via the DATA filehandle if desired).
HOME Used if chdir has no argument.
LOGDIR Used if chdir has no argument and HOME is not
set.
PATH Used in executing subprocesses, and in finding
the program if -S is used.
PERL5LIB A list of directories in which to look for
Perl library files before looking in the standard
library and the current directory. Any
architecture-specific directories under the
specified locations are automatically included
if they exist. If PERL5LIB is not defined,
PERLLIB is used. Directories are separated
(like in PATH) by a colon on unixish platforms
and by a semicolon on Windows (the proper path
separator being given by the command "perl
-V:path_sep").
When running taint checks (either because the
program was running setuid or setgid, or the
-T switch was used), neither variable is used.
The program should instead say:
use lib "/my/directory";
PERL5OPT Command-line options (switches). Switches in
this variable are taken as if they were on
every Perl command line. Only the -[DIMUdmtw]
switches are allowed. When running taint
checks (because the program was running setuid
or setgid, or the -T switch was used), this
variable is ignored. If PERL5OPT begins with
-T, tainting will be enabled, and any subsequent
options ignored.
PERLIO A space (or colon) separated list of PerlIO
layers. If perl is built to use PerlIO system
for IO (the default) these layers effect
perl's IO.
It is conventional to start layer names with a
colon e.g. ":perlio" to emphasise their similarity
to variable "attributes". But the code
that parses layer specification strings (which
is also used to decode the PERLIO environment
variable) treats the colon as a separator.
An unset or empty PERLIO is equivalent to
":stdio".
The list becomes the default for all perl's
IO. Consequently only built-in layers can
appear in this list, as external layers (such
as :encoding()) need IO in order to load
them!. See "open pragma" for how to add external
encodings as defaults.
The layers that it makes sense to include in
the PERLIO environment variable are briefly
summarised below. For more details see PerlIO.
:bytes A pseudolayer that turns off the
":utf8" flag for the layer below.
Unlikely to be useful on its own in
the global PERLIO environment variable.
You perhaps were thinking of
":crlf:bytes" or ":perlio:bytes".
:crlf A layer which does CRLF to "0 translation
distinguishing "text" and
"binary" files in the manner of MS-DOS
and similar operating systems. (It
currently does not mimic MS-DOS as far
as treating of Control-Z as being an
end-of-file marker.)
:mmap A layer which implements "reading" of
files by using "mmap()" to make
(whole) file appear in the process's
address space, and then using that as
PerlIO's "buffer".
:perlio This is a re-implementation of
"stdio-like" buffering written as a
PerlIO "layer". As such it will call
whatever layer is below it for its
operations (typically ":unix").
:pop An experimental pseudolayer that
removes the topmost layer. Use with
the same care as is reserved for
nitroglycerin.
:raw A pseudolayer that manipulates other
layers. Applying the ":raw" layer is
equivalent to calling "binmode($fh)".
It makes the stream pass each byte asis
without any translation. In particular
CRLF translation, and/or :utf8
intuited from locale are disabled.
Unlike in the earlier versions of Perl
":raw" is not just the inverse of
":crlf" - other layers which would
affect the binary nature of the stream
are also removed or disabled.
:stdio This layer provides PerlIO interface
by wrapping system's ANSI C "stdio"
library calls. The layer provides both
buffering and IO. Note that ":stdio"
layer does not do CRLF translation
even if that is platforms normal
behaviour. You will need a ":crlf"
layer above it to do that.
:unix Low level layer which calls "read",
"write" and "lseek" etc.
:utf8 A pseudolayer that turns on a flag on
the layer below to tell perl that output
should be in utf8 and that input
should be regarded as already in utf8
form. May be useful in PERLIO environment
variable to make UTF-8 the
default. (To turn off that behaviour
use ":bytes" layer.)
:win32 On Win32 platforms this experimental
layer uses native "handle" IO rather
than unix-like numeric file descriptor
layer. Known to be buggy in this
release.
On all platforms the default set of layers
should give acceptable results.
For UNIX platforms that will equivalent of
"unix perlio" or "stdio". Configure is setup
to prefer "stdio" implementation if system's
library provides for fast access to the
buffer, otherwise it uses the "unix perlio"
implementation.
On Win32 the default in this release is "unix
crlf". Win32's "stdio" has a number of
bugs/mis-features for perl IO which are somewhat
C compiler vendor/version dependent.
Using our own "crlf" layer as the buffer
avoids those issues and makes things more uniform.
The "crlf" layer provides CRLF to/from
"0 conversion as well as buffering.
This release uses "unix" as the bottom layer
on Win32 and so still uses C compiler's
numeric file descriptor routines. There is an
experimental native "win32" layer which is
expected to be enhanced and should eventually
be the default under Win32.
PERLIO_DEBUG
If set to the name of a file or device then
certain operations of PerlIO sub-system will
be logged to that file (opened as append).
Typical uses are UNIX:
PERLIO_DEBUG=/dev/tty perl script ...
and Win32 approximate equivalent:
set PERLIO_DEBUG=CON
perl script ...
PERLLIB A list of directories in which to look for
Perl library files before looking in the standard
library and the current directory. If
PERL5LIB is defined, PERLLIB is not used.
PERL5DB The command used to load the debugger code.
The default is:
BEGIN { require 'perl5db.pl' }
PERL5SHELL (specific to the Win32 port)
May be set to an alternative shell that perl
must use internally for executing "backtick"
commands or system(). Default is "cmd.exe
/x/d/c" on WindowsNT and "command.com /c" on
Windows95. The value is considered to be
space-separated. Precede any character that
needs to be protected (like a space or backslash)
with a backslash.
Note that Perl doesn't use COMSPEC for this
purpose because COMSPEC has a high degree of
variability among users, leading to portability
concerns. Besides, perl can use a shell
that may not be fit for interactive use, and
setting COMSPEC to such a shell may interfere
with the proper functioning of other programs
(which usually look in COMSPEC to find a shell
fit for interactive use).
PERL_DEBUG_MSTATS
Relevant only if perl is compiled with the
malloc included with the perl distribution
(that is, if "perl -V:d_mymalloc" is
'define'). If set, this causes memory statistics
to be dumped after execution. If set to
an integer greater than one, also causes memory
statistics to be dumped after compilation.
PERL_DESTRUCT_LEVEL
Relevant only if your perl executable was
built with -DDEBUGGING, this controls the
behavior of global destruction of objects and
other references. See "PERL_DESTRUCT_LEVEL"
in perlhack for more information.
PERL_DL_NONLAZY
Set to one to have perl resolve all undefined
symbols when it loads a dynamic library. The
default behaviour is to resolve symbols when
they are used. Setting this variable is useful
during testing of extensions as it ensures
that you get an error on misspelled function
names even if the test suite doesn't call it.
PERL_ENCODING
If using the "encoding" pragma without an
explicit encoding name, the PERL_ENCODING
environment variable is consulted for an
encoding name.
PERL_HASH_SEED
(Since Perl 5.8.1.) Used to randomise Perl's
internal hash function. To emulate the
pre-5.8.1 behaviour, set to an integer (zero
means exactly the same order as 5.8.0).
"Pre-5.8.1" means, among other things, that
hash keys will be ordered the same between
different runs of Perl.
The default behaviour is to randomise unless
the PERL_HASH_SEED is set. If Perl has been
compiled with "-DUSE_HASH_SEED_EXPLICIT", the
default behaviour is not to randomise unless
the PERL_HASH_SEED is set.
If PERL_HASH_SEED is unset or set to a nonnumeric
string, Perl uses the pseudorandom
seed supplied by the operating system and
libraries. This means that each different run
of Perl will have a different ordering of the
results of keys(), values(), and each().
Please note that the hash seed is sensitive [Toc] [Back]
information. Hashes are randomized to protect
against local and remote attacks against Perl
code. By manually setting a seed this protection
may be partially or completely lost.
See "Algorithmic Complexity Attacks" in
perlsec and "PERL_HASH_SEED_DEBUG" for more
information.
PERL_HASH_SEED_DEBUG
(Since Perl 5.8.1.) Set to one to display (to
STDERR) the value of the hash seed at the
beginning of execution. This, combined with
"PERL_HASH_SEED" is intended to aid in debugging
nondeterministic behavior caused by hash
randomization.
Note that the hash seed is sensitive informa- [Toc] [Back]
tion: by knowing it one can craft a denial-ofservice
attack against Perl code, even
remotely, see "Algorithmic Complexity Attacks"
in perlsec for more information. Do not dis-
close the hash seed to people who don't need
to know it. See also hash_seed() of
Hash::Util.
PERL_ROOT (specific to the VMS port)
A translation concealed rooted logical name
that contains perl and the logical device for
the @INC path on VMS only. Other logical
names that affect perl on VMS include PERLSHR,
PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL
but are optional and discussed further in perlvms
and in README.vms in the Perl source distribution.
PERL_SIGNALS
In Perls 5.8.1 and later. If set to "unsafe"
the pre-Perl-5.8.0 signals behaviour (immediate
but unsafe) is restored. If set to "safe"
the safe (or deferred) signals are used. See
"Deferred Signals (Safe signals)" in perlipc.
PERL_UNICODE
Equivalent to the -C command-line switch.
Note that this is not a boolean variable--
setting this to "1" is not the right way to
"enable Unicode" (whatever that would mean).
You can use "0" to "disable Unicode", though
(or alternatively unset PERL_UNICODE in your
shell before starting Perl). See the description
of the "-C" switch for more information.
SYS$LOGIN (specific to the VMS port)
Used if chdir has no argument and HOME and
LOGDIR are not set.
Perl also has environment variables that control how Perl
handles data specific to particular natural languages.
See perllocale.
Apart from these, Perl uses no other environment variables,
except to make them available to the program being
executed, and to child processes. However, programs running
setuid would do well to execute the following lines
before doing anything else, just to keep people honest:
$ENV{PATH} = '/bin:/usr/bin'; # or whatever you
need
$ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
perl v5.8.5 2002-11-06 24 [ Back ] |
