perlrun - how to execute the Perl interpreter
perl [ -sTtuUWX ] [ -hv ] [ -V[:configvar] ] [ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ] [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ] [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -f ] [ -C [number/list] ] [ -S ] [ -x[dir] ] [ -i[extension] ] [ [-e|-E] 'command' ] [ -- ] [ programfile ] [ argument ]...
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:
Specified line by line via -e or -E switches on the command line.
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".)
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 behaviour 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{ $/ = "\0digits"; }.
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 -x -wS $0 ${1+"$@"}'
if 0;to let Perl see the "-p" switch.
A similar trick involves the env program, if you have it.
#!/usr/bin/env perlThe 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, perl5.14.1, you should place that directly in the #! line's path.
If the #! line does not contain the word "perl" nor the word "indir", 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 part-way 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.
Unix's #! technique can be simulated on other systems:
Put
extproc perl -S -your_switchesas the first line in *.cmd file ("-S" due to a bug in cmd.exe's `extproc' handling).
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).
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.
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 (*, \ and " are common) and how to protect whitespace 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 world\n"'
# MS-DOS, etc.
perl -e "print \"Hello world\n\""
# VMS
perl -e "print ""Hello world\n"""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 world\n<Ctrl-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.
There is no general solution to all of this. It's just a mess.
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/perl5.14or if you just want to be running at least version, place a statement like this at the top of your program:
use 5.014;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.origA -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments.
Switches include:
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 unlinkThe special value 00 will cause Perl to slurp files in paragraph mode. Any value 0400 or above will cause Perl to slurp files whole, but by convention the value 0777 is the one normally used for this purpose.
You can also specify the separator character using hexadecimal notation: -0xHHH..., where the H are valid hexadecimal digits. Unlike the octal form, this one may be used to specify any Unicode character, even those beyond 0xFF. So if you really want a record separator of 0777, specify it as -0x1FF. (This means that you cannot use the "-x" option with a directory name that consists of hexadecimal digits, or else Perl will think you have specified a hex number to -0.)
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), "\n";'is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}An alternate delimiter may be specified using -F.
-a implicitly sets "-n".
The -C flag controls some 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_CTYPE, and LANG, in the order of
decreasing precedence) -- if the variables indicate
UTF-8, then the selected "IOEioA" are in effect
a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
code in debugging mode.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) in main program scope 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 set via ${^OPEN}, with explicit layers in open() and with binmode() one can manipulate streams as usual. This has no effect on code run in modules.
-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. (See "UTF-8 no longer default under UTF-8 locales" in perl581delta.)
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 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 two-arg 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 Unicode-aware "wide system call" Win32 APIs. This feature was practically unused, however, and the command line switch was therefore "recycled".)
Note: Since perl 5.10.1, if the -C option is used on the #! line, it must be specified on the command line as well, since the standard streams are already set up at this point in the execution of the perl interpreter. You can also use binmode() to set the encoding of an I/O stream.
causes Perl to check the syntax of the program and then exit without executing it. Actually, it will execute any BEGIN, UNITCHECK, or CHECK blocks and any use statements: these are considered as occurring outside the execution of your program. INIT and END blocks, however, will be skipped.
runs the program under the Perl debugger. See perldebug. If t is specified, it indicates to the debugger that threads will be used in the code being debugged.
runs the program under the control of a debugging, profiling, or tracing module installed as Devel::MOD. E.g., -d:DProf executes the program using the Devel::DProf profiler. As with the -M flag, options may be passed to the Devel::MOD package where they will be received and interpreted by the Devel::MOD::import routine. Again, like -M, use --d:-MOD to call Devel::MOD::unimport instead of import. The comma-separated list of options must follow a = character. If t is specified, it indicates to the debugger that threads will be used in the code being debugged. See perldebug.
sets debugging flags. This switch is enabled only if your perl binary has been built with debugging enabled: normal production perls won't have been.
For example, to watch how perl executes your program, use -Dtls. 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 (with v, displays parse
stack)
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, source file input state
128 m Memory and SV allocation
256 f Format processing
512 r Regular expression parsing and execution
1024 x Syntax tree dump
2048 u Tainting checks
4096 U Unofficial, User hacking (reserved for private,
unreleased use)
16384 X Scratchpad allocation
32768 D Cleaning up
65536 S Op slab allocation
131072 T Tokenizing
262144 R Include reference counts of dumped variables
(eg when using -Ds)
524288 J show s,t,P-debug (don't Jump over) on opcodes within
package DB
1048576 v Verbose: use in conjunction with other flags to
increase the verbosity of the output. Is a no-op on
many of the other flags
2097152 C Copy On Write
4194304 A Consistency checks on internal structures
8388608 q quiet - currently only suppresses the "EXECUTING"
message
16777216 M trace smart match resolution
33554432 B dump suBroutine definitions, including special
Blocks like BEGIN
67108864 L trace Locale-related info; what gets output is very
subject to change
134217728 i trace PerlIO layer processing. Set PERLIO_DEBUG to
the filename to trace to.
268435456 y trace y///, tr/// compilation and executionAll these flags require -DDEBUGGING when you compile the Perl executable (but see :opd in Devel::Peek or "'debug' mode" in re which may change this). See the INSTALL file in the Perl source distribution for how to do this.
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.
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.
behaves just like -e, except that it implicitly enables all optional features (in the main compilation unit). See feature.
Disable executing $Config{sitelib}/sitecustomize.pl at startup.
Perl can be built so that it by default will try to execute $Config{sitelib}/sitecustomize.pl at startup (in a BEGIN block). This is a hook that allows the sysadmin to customize how Perl behaves. It can for instance be used to add entries to the @INC array to make Perl find modules in non-standard locations.
Perl actually inserts the following code:
BEGIN {
do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
&& do "$Config{sitelib}/sitecustomize.pl";
}Since it is an actual do (not a require), sitecustomize.pl doesn't need to return a true value. The code is run in package main, in its own lexical scope. However, if the script dies, $@ will not be set.
The value of $Config{sitelib} is also determined in C code and not read from Config.pm, which is not loaded.
The code is executed very early. For example, any changes made to @INC will show up in the output of `perl -V`. Of course, END blocks will be likewise executed very late.
To determine at runtime if this capability has been compiled in your perl, you can check the value of $Config{usesitecustomize}.
specifies the pattern to split on for "-a". The pattern may be surrounded by //, "", or '', otherwise it will be put in single quotes. You can't use literal whitespace or NUL characters in the pattern.
prints a summary of the options.
specifies that files processed by the <> construct are to be edited in-place. It does this by renaming the input file, opening the output file by the original name, and selecting that output file as the default for print() statements. The extension, if supplied, is used to modify the name of the old file to make a backup copy, following these rules:
If no extension is supplied, and your system supports it, the original file is kept open without a name while the output is redirected to a new file with the original filename. When perl exits, cleanly or not, the original file is unlinked.
If the extension doesn't contain a *, then it is appended to the end of the current filename as a suffix. If the extension does contain one or more * characters, then each * is replaced with the current filename. In Perl terms, you could think of this as:
($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 read-only 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...Note that because -i renames or deletes the original file before creating a new file of the same name, Unix-style soft and hard links will not be preserved.
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.
Directories specified by -I are prepended to the search path for modules (@INC).
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 $\ (the output record separator) to have the value of octnum so that any print statements will have that separator added back on. If octnum is omitted, sets $\ to the current value of $/. For instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 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 $\ to newline and then sets $/ to the null character.