Finds the statement labeled with LABEL and resumes execution there. Currently you may only go to statements in the main body of the program that are not nested inside a do {} construct. This statement is not implemented very efficiently, and is here only to make the sed-to-perl translator easier. Use at your own risk. Returns the decimal value of EXPR interpreted as an hex string. (To interpret strings that might start with 0 or 0x see oct().) Returns the position of SUBSTR in STR, based at 0, or whatever you've set the $[ variable to. If the substring is not found, returns one less than the base, ordinarily -1. Returns the integer portion of EXPR. Joins the separate strings of LIST or ARRAY into a single string with fields separated by the value of EXPR, and returns the string. Example:

    $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
See Returns a normal array consisting of all the keys of the named associative array. The keys are returned in an apparently random order, but it is the same order as either the values() or each() function produces (given that the associative array has not been modified). Here is yet another way to print your environment:
	@keys = keys(ENV);
	@values = values(ENV);
	while ($#keys >= 0) {
		print pop(keys),'=',pop(values),";
	}
Sends a signal to a list of processes. The first element of the list must be the (numerical) signal to send. LIST may be an array, in which case you may wish to use the unshift command to put the signal on the front of the array. Returns the number of processes successfully signaled. Note: in order to use the value you must put the whole thing in parentheses:
	$cnt = (kill 9,$child1,$child2);
The command is like the statement in C (as used in loops); it immediately exits the loop in question. If the LABEL is omitted, the command refers to the innermost enclosing loop. The block, if any, is not executed:
	line: while (<stdin>) {
		last line if /^$/;	# exit when done with header
		...
	}
Converts a time as returned by the time function to a 9-element array with the time analyzed for the local timezone. Typically used as follows:
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)
       = localtime(time);
All array elements are numeric. Returns logarithm (base e) of EXPR. The command is like the statement in C; it starts the next iteration of the loop:
	line: while (<stdin>) {
		next line if /^#/;	# discard comments
		...
	}
Note that if there were a block on the above, it would get executed even on discarded lines. If the LABEL is omitted, the command refers to the innermost enclosing loop. Returns the length in characters of the value of EXPR. Creates a new filename linked to the old filename. Returns 1 for success, 0 otherwise. Returns the decimal value of EXPR interpreted as an octal string. (If EXPR happens to start off with 0x, interprets it as a hex string instead.) The following will handle decimal, octal and hex in the standard notation:
	$val = oct($val) if $val =~ /^0/;
Opens the file whose filename is given by EXPR, and associates it with FILEHANDLE. If EXPR is omitted, the string variable of the same name as the FILEHANDLE contains the filename. If the filename begins with ">", the file is opened for output. If the filename begins with ">>", the file is opened for appending. If the filename begins with "|", the filename is interpreted as a command to which output is to be piped, and if the filename ends with a "|", the filename is interpreted as command which pipes input to us. (You may not have a command that pipes both in and out.) Opening '-' opens stdin and opening '>-' opens stdout. Open returns 1 upon success, '' otherwise. Examples:

    $article = 100;
    open article || die "Can't find article $article";
    while (<article>) {...
    open(log, '>>/usr/spool/news/twitlog');
    open(article, "caeser <$article |");		# decrypt article
    open(extract, "|sort >/tmp/Tmp$$");		# $$ is our process#
Returns the ascii value of the first character of EXPR. Pops and returns the last value of the array, shortening the array by 1. Prints a string or comma-separated list of strings. If FILEHANDLE is omitted, prints by default to standard output (or to the last selected output channel--see select()). If LIST is also omitted, prints $_ to stdout. LIST may also be an array value. To set the default output channel to something other than stdout use the select operation. Equivalent to a "print FILEHANDLE sprintf(LIST)". Treats ARRAY (@ is optional) as a stack, and pushes the value of EXPR onto the end of ARRAY. The length of ARRAY increases by 1. Has the same effect as
    $ARRAY[$#ARRAY+1] = EXPR;
but is more efficient. The command restarts the loop block without evaluating the conditional again. The block, if any, is not executed. If the LABEL is omitted, the command refers to the innermost enclosing loop. This command is normally used by programs that want to lie to themselves about what was just input:
	# a simpleminded Pascal comment stripper
	# (warning: assumes no { or } in strings)
	line: while (<stdin>) {
		while (s|({.*}.*){.*}|$1 |) {}
		s|{.*}| |;
		if (s|{.*| |) {
			$front = $_;
			while (<stdin>) {
				if (/}/) {	# end of comment?
					s|^|$front{|;
					redo line;
				}
			}
		}
		print;
	}
Changes the name of a file. Returns 1 for success, 0 otherwise. Generally used in a block at the end of a loop to clear variables and reset ?? searches so that they work again. The expression is interpreted as a list of single characters (hyphens allowed for ranges). All string variables beginning with one of those letters are set to the null string. If the expression is omitted, one-match searches (?pattern?) are reset to match again. Always returns 1. Examples:
    reset 'X';	# reset all X variables
    reset 'a-z';# reset lower case variables
    reset;	# just reset ?? searches
Searches a string for a pattern, and if found, replaces that pattern with the replacement text and returns the number of substitutions made. Otherwise it returns false (0). The "g" is optional, and if present, indicates that all occurences of the pattern are to be replaced. Any delimiter may replace the slashes; if single quotes are used, no interpretation is done on the replacement string. If no string is specified via the =~ or !~ operator, the $_ string is searched and modified. (The string specified with =~ must be a string variable or array element, i.e. an lvalue.) If the pattern contains a $ that looks like a variable rather than an end-of-string test, the variable will be interpolated into the pattern at run-time. See also the section on regular expressions. Examples:
    s/\bgreen\b/mauve/g;		# don't change wintergreen
    $path =~ s|/usr/bin|/usr/local/bin|;
    s/Login: $foo/Login: $bar/; # run-time pattern
    s/([^ ]*) *([^ ]*)/$2 $1/;	# reverse 1st two fields
(Note the use of $ instead of \ in the last example. See section on regular expressions.) Randomly positions the file pointer for FILEHANDLE, just like the fseek() call of stdio. Returns 1 upon success, 0 otherwise. Sets the current default filehandle for output. This has two effects: first, a or a without a filehandle will default to this FILEHANDLE. Second, references to variables related to output will refer to this output channel. For example, if you have to set the top of form format for more than one output channel, you might do the following:
    select(report1);
    $^ = 'report1_top';
    select(report2);
    $^ = 'report2_top';
Select happens to return TRUE if the file is currently open and FALSE otherwise, but this has no effect on its operation. Shifts the first value of the array off, shortening the array by 1 and moving everything down. If ARRAY is omitted, shifts the ARGV array. See also unshift(), push() and pop(). Shift() and unshift() do the same thing to the left end of an array that push() and pop() do to the right end. Causes the script to sleep for EXPR seconds, or forever if no EXPR. May be interrupted by sending the process a SIGALARM. Returns the number of seconds actually slept. Splits a string into an array of strings, and returns it. If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, splits on whitespace (/[ \t\n]+/). Anything matching PATTERN is taken to be a delimiter separating the fields. (Note that the delimiter may be longer than one character.) Trailing null fields are stripped, which potential users of pop() would do well to remember. A pattern matching the null string (not to be confused with a null pattern) will split the value of EXPR into separate characters at each point it matches that way. For example:
	print join(':',split(/ */,'hi there'));
produces the output 'h:i:t:h:e:r:e'. The pattern /PATTERN/ may be replaced with an expression to specify patterns that vary at runtime. As a special case, specifying a space (' ') will split on white space just as split with no arguments does, but leading white space does NOT produce a null first field. Thus, split(' ') can be used to emulate awk's default behavior, whereas split(/ /) will give you as many null initial fields as there are leading spaces.

Example:
	open(passwd, '/etc/passwd');
	while (<passwd>) {
($login, $passwd, $uid, $gid, $gcos, $home, $shell)
			= split(/:/);
		...
	}
(Note that $shell above will still have a newline on it. See chop().) See also Returns a string formatted by the usual printf conventions. The * character is not supported. Return the square root of EXPR. Returns a 13-element array giving the statistics for a file, either the file opened via FILEHANDLE, or named by EXPR. Typically used as follows:
    ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
       $atime,$mtime,$ctime,$blksize,$blocks)
           = stat($filename);
Extracts a substring out of EXPR and returns it. First character is at offset 0, or whatever you've set $[ to. Does exactly the same thing as "exec LIST" except that a fork is done first, and the parent process waits for the child process to complete. Note that argument processing varies depending on the number of arguments. The return value is the exit status of the program. See exec. Returns the current file position for FILEHANDLE. If FILEHANDLE is omitted, assumes the file last read. Returns the number of seconds since January 1, 1970. Suitable for feeding to gmtime() and localtime(). Returns a four-element array giving the user and system times, in seconds, for this process and the children of this process.

($user,$system,$cuser,$csystem) = times;

Translates all occurences of the characters found in the search list with the corresponding character in the replacement list. It returns the number of characters replaced. If no string is specified via the =~ or !~ operator, the $_ string is translated. (The string specified with =~ must be a string variable or array element, i.e. an lvalue.) For devotees, is provided as a synonym for Examples:
    $ARGV[1] =~ y/A-Z/a-z/;	# canonicalize to lower case
    $cnt = tr/*/*/;		# count the stars in $_
Sets the umask for the process and returns the old one. Deletes a list of files. LIST may be an array. Returns the number of files successfully deleted. Note: in order to use the value you must put the whole thing in parentheses:
	$cnt = (unlink 'a','b','c');
Does the opposite of a shift. Prepends list to the front of the array, and returns the number of elements in the new array.
	unshift(ARGV,'-e') unless $ARGV[0] =~ /^-/;
Returns a normal array consisting of all the values of the named associative array. The values are returned in an apparently random order, but it is the same order as either the keys() or each() function produces (given that the associative array has not been modified). See also keys() and each(). Writes a formatted record (possibly multi-line) to the specified file, using the format associated with that file. By default the format for a file is the one having the same name is the filehandle, but the format for the current output channel (see may be set explicitly by assigning the name of the format to the $~ variable.

Top of form processing is handled automatically: if there is insufficient room on the current page for the formatted record, the page is advanced, a special top-of-page format is used to format the new page header, and then the record is written. By default the top-of-page format is "top", but it may be set to the format of your choice by assigning the name to the $^ variable.

If FILEHANDLE is unspecified, output goes to the current default output channel, which starts out as stdout but may be changed by the operator. If the FILEHANDLE is an EXPR, then the expression is evaluated and the resulting string is used to look up the name of the FILEHANDLE at run time. For more on formats, see the section on formats later on.

Subroutines
A subroutine may be declared as follows:
    sub NAME BLOCK
Any arguments passed to the routine come in as array @_, that is ($_[0], $_[1], ...). The return value of the subroutine is the value of the last expression evaluated. There are no local variables--everything is a global variable. A subroutine is called using the operator. (CAVEAT: For efficiency reasons recursive subroutine calls are not currently supported. This restriction may go away in the future. Then again, it may not.)
Example:
	sub MAX {
		$max = pop(@_);
		while ($foo = pop(@_)) {
			$max = $foo if $max < $foo;
		}
		$max;
	}
	...
	$bestday = do MAX($mon,$tue,$wed,$thu,$fri);
Example:
	# get a line, combining continuation lines
	#  that start with whitespace
	sub get_line {
		$thisline = $lookahead;
		line: while ($lookahead = <stdin>) {
			if ($lookahead =~ /^[ \t]/) {
				$thisline .= $lookahead;
			}
			else {
				last line;
			}
		}
		$thisline;
	}
	$lookahead = <stdin>;	# get first line
	while ($_ = get_line()) {
		...
	}
Use array assignment to name your formal arguments:
	sub maybeset {
		($key,$value) = @_;
		$foo{$key} = $value unless $foo{$key};
	}

Regular Expressions
The patterns used in pattern matching are regular expressions such as those used by In addition, \w matches an alphanumeric character and \W a nonalphanumeric. Word boundaries may be matched by \b, and non-boundaries by \B. The bracketing construct ( ... ) may also be used, $<digit> matches the digit'th substring, where digit can range from 1 to 9. (You can also use the old standby \<digit> in search patterns, but $<digit> also works in replacement patterns and in the block controlled by the current conditional.) $+ returns whatever the last bracket match matched. $& returns the entire matched string. Up to 10 alternatives may given in a pattern, separated by |, with the caveat that ( ... | ... ) is illegal. Examples:

	s/^([^ ]*) *([^ ]*)/$2 $1/;	# swap first two words
	if (/Time: (..):(..):(..)/) {
		$hours = $1;
		$minutes = $2;
		$seconds = $3;
	}
By default, the ^ character matches only the beginning of the string, and does certain optimizations with the assumption that the string contains only one line. You may, however, wish to treat a string as a multi-line buffer, such that the ^ will match after any newline within the string. At the cost of a little more overhead, you can do this by setting the variable $* to 1. Setting it back to 0 makes revert to its old behavior.

Formats
Output record formats for use with the operator may declared as follows:
    format NAME =
    FORMLIST
    .
If name is omitted, format "stdout" is defined. FORMLIST consists of a sequence of lines, each of which may be of one of three types: A comment. A "picture" line giving the format for one output line. An argument line supplying values to plug into a picture line. Picture lines are printed exactly as they look, except for certain fields that substitute values into the line. Each picture field starts with either @ or ^. The @ field (not to be confused with the array marker @) is the normal case; ^ fields are used to do rudimentary multi-line text block filling. The length of the field is supplied by padding out the field with multiple <, >, or | characters to specify, respectively, left justfication, right justification, or centering. If any of the values supplied for these fields contains a newline, only the text up to the newline is printed. The special field @* can be used for printing multi-line values. It should appear by itself on a line. The values are specified on the following line, in the same order as the picture fields. They must currently be either string variable names or string literals (or pseudo-literals). Currently you can separate values with spaces, but commas may be placed between values to prepare for possible future versions in which full expressions are allowed as values. Picture fields that begin with ^ rather than @ are treated specially. The value supplied must be a string variable name which contains a text string. puts as much text as it can into the field, and then chops off the front of the string so that the next time the string variable is referenced, more of the text can be printed. Normally you would use a sequence of fields in a vertical stack to print out a block of text. If you like, you can end the final field with ..., which will appear in the output if the text was too long to appear in its entirety. Since use of ^ fields can produce variable length records if the text to be formatted is short, you can suppress blank lines by putting the tilde (~) character anywhere in the line. (Normally you should put it in the front if possible.) The tilde will be translated to a space upon output. Examples:
# a report on the /etc/passwd file
format top =
                        Passwd File
Name                Login    Office   Uid   Gid Home
------------------------------------------------------------------
.
format stdout =
@<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
$name               $login   $office $uid $gid  $home
.
# a report from a bug report form
format top =
                        Bug Reports
@<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
$system;                      $%;         $date
------------------------------------------------------------------
.
format stdout =
Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
         $subject
Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
       $index                        $description
Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
          $priority         $date    $description
From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
      $from                          $description
Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
             $programmer             $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...
                                     $description
.
It is possible to intermix prints with writes on the same output channel,
but you'll have to handle $- (lines left on the page) yourself.
If you are printing lots of fields that are usually blank, you should consider using the reset operator between records. Not only is it more efficient, but it can prevent the bug of adding another field and forgetting to zero it.

Predefined Names
The following names have special meaning to I could have used alphabetic symbols for some of these, but I didn't want to take the chance that someone would say reset "a-zA-Z" and wipe them all out. You'll just have to suffer along with these silly symbols. Most of them have reasonable mnemonics, or analogues in one of the shells. The default input and pattern-searching space. The following pairs are equivalent:
	while (<>) {...	# only equivalent in while!
	while ($_ = <>) {...
	/^Subject:/
	$_ =~ /^Subject:/
	y/a-z/A-Z/
	$_ =~ y/a-z/A-Z/
	chop
	chop($_)
(Mnemonic: underline is understood in certain operations.) The current input line number of the last file that was read. Readonly. (Mnemonic: many programs use . to mean the current line number.) The input record separator, newline by default. Works like awk's RS variable, including treating blank lines as delimiters if set to the null string. If set to a value longer than one character, only the first character is used. (Mnemonic: / is used to delimit line boundaries when quoting poetry.) The output field separator for the print operator. Ordinarily the print operator simply prints out the comma separated fields you specify. In order to get behavior more like awk, set this variable as you would set awk's OFS variable to specify what is printed between fields. (Mnemonic: what is printed when there is a , in your print statement.) The output record separator for the print operator. Ordinarily the print operator simply prints out the comma separated fields you specify, with no trailing newline or record separator assumed. In order to get behavior more like awk, set this variable as you would set awk's ORS variable to specify what is printed at the end of the print. (Mnemonic: you set $\ instead of adding \n at the end of the print. Also, it's just like /, but it's what you get "back" from perl.) The output format for printed numbers. This variable is a half-hearted attempt to emulate awk's OFMT variable. There are times, however, when awk and perl have differing notions of what is in fact numeric. Also, the initial value is %.20g rather than %.6g, so you need to set $# explicitly to get awk's value. (Mnemonic: # is the number sign.) The current page number of the currently selected output channel. (Mnemonic: % is page number in nroff.) The current page length (printable lines) of the currently selected output channel. Default is 60. (Mnemonic: = has horizontal lines.) The number of lines left on the page of the currently selected output channel. (Mnemonic: lines_on_page - lines_printed.) The name of the current report format for the currently selected output channel. (Mnemonic: brother to $^.) The name of the current top-of-page format for the currently selected output channel. (Mnemonic: points to top of page.) If set to nonzero, forces a flush after every write or print on the currently selected output channel. Default is 0. Note that stdout will typically be line buffered if output is to the terminal and block buffered otherwise. Setting this variable is useful primarily when you are outputting to a pipe, such as when you are running a perl script under rsh and want to see the output as it's happening. (Mnemonic: when you want your pipes to be piping hot.) The process number of the running this script. (Mnemonic: same as shells.) The status returned by the last backtick (``) command. (Mnemonic: same as sh and ksh.) The last bracket matched by the last search pattern. This is useful if you don't know which of a set of alternative patterns matched. For example:
    /Version: (.*)|Revision: (.*)/ && ($rev = $+);
(Mnemonic: be positive and forward looking.) Set to 1 to do multiline matching within a string, 0 to assume strings contain a single line. Default is 0. (Mnemonic: * matches multiple things.) Contains the name of the file containing the script being executed. The value should be copied elsewhere before any pattern matching happens, which clobbers $0. (Mnemonic: same as sh and ksh.) Contains the subpattern from the corresponding set of parentheses in the last pattern matched, not counting patterns matched in nested blocks that have been exited already. (Mnemonic: like \digit.) The index of the first element in an array, and of the first character in a substring. Default is 0, but you could set it to 1 to make behave more like (or Fortran) when subscripting and when evaluating the index() and substr() functions. (Mnemonic: [ begins subscripts.) The current value of errno, with all the usual caveats. (Mnemonic: What just went bang?) The error message from the last eval command. If null, the last eval parsed and executed correctly. (Mnemonic: Where was the syntax error "at"?) The array ARGV contains the command line arguments intended for the script. Note that $#ARGV is the generally number of arguments minus one, since $ARGV[0] is the first argument, NOT the command name. See $0 for the command name. The associative array ENV contains your current environment. Setting a value in ENV changes the environment for child processes. The associative array SIG is used to set signal handlers for various signals. Example:
	sub handler {	# 1st argument is signal name
		($sig) = @_;
		print "Caught a SIG$sig--shutting down;
		close(log);
		exit(0);
	}
	$SIG{'INT'} = 'handler';
	$SIG{'QUIT'} = 'handler';
	...
	$SIG{'INT'} = 'DEFAULT';	# restore default action
	$SIG{'QUIT'} = 'IGNORE';	# ignore SIGQUIT
currently uses no environment variables, except to make them available to the script being executed, and to child processes. However, scripts 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 $ENV{'SHELL'};
    $ENV{'IFS'} = '' if $ENV{'IFS'};
Larry Wall <lwall@jpl-devvax.Jpl.Nasa.Gov> /tmp/perl-eXXXXXX temporary file for commands. a2p awk to perl translator
s2p sed to perl translator
perldb interactive perl debugger Compilation errors will tell you the line number of the error, with an indication of the next token or token type that was to be examined. (In the case of a script passed to via switches, each is counted as one line.) Accustomed awk users should take special note of the following: Semicolons are required after all simple statements in perl. Newline is not a statement delimiter. Curly brackets are required on ifs and whiles. Variables begin with $ or @ in perl. Arrays index from 0 unless you set $[. Likewise string positions in substr() and index(). You have to decide whether your array has numeric or string indices. You have to decide whether you want to use string or numeric comparisons. Reading an input line does not split it for you. You get to split it yourself to an array. And split has different arguments. The current input line is normally in $_, not $0. It generally does not have the newline stripped. ($0 is initially the name of the program executed, then the last matched string.) The current filename is $ARGV, not $FILENAME. NR, RS, ORS, OFS, and OFMT have equivalents with other symbols. FS doesn't have an equivalent, since you have to be explicit about split statements. $<digit> does not refer to fields--it refers to substrings matched by the last match pattern. The print statement does not add field and record separators unless you set $, and $\. You must open your files before you print to them. The range operator is "..", not comma. (The comma operator works as in C.) The match operator is "=~", not "~". ("~" is the one's complement operator.) The concatenation operator is ".", not the null string. (Using the null string would render "/pat/ /pat/" unparseable, since the third slash would be interpreted as a division operator--the tokener is in fact slightly context sensitive for operators like /, ?, and <. And in fact, . itself can be the beginning of a number.) The \nnn construct in patterns must be given as [\nnn] to avoid interpretation as a backreference. Next, exit, and continue work differently. When in doubt, run the awk construct through a2p and see what it gives you. Cerebral C programmers should take note of the following: Curly brackets are required on ifs and whiles. You should use "elsif" rather than "else if" Break and continue become last and next, respectively. There's no switch statement. Variables begin with $ or @ in perl. Printf does not implement *. Comments begin with #, not /*. You can't take the address of anything. Subroutines are not reentrant. ARGV must be capitalized. The "system" calls link, unlink, rename, etc. return 1 for success, not 0. Signal handlers deal with signal names, not numbers. Seasoned sed programmers should take note of the following: Backreferences in substitutions use $ rather than \. The pattern matching metacharacters (, ), and | do not have backslashes in front. You can't currently dereference array elements inside a double-quoted string. You must assign them to a temporary and interpolate that. Associative arrays really ought to be first class objects. Recursive subroutines are not currently supported, due to the way temporary values are stored in the syntax tree. Arrays ought to be passable to subroutines just as strings are. The array literal consisting of one element is currently misinterpreted, i.e.
	@array = (123);
doesn't work right. actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.