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PERLOP(1) User Contributed Perl Documentation PERLOP(1) NNNNAAAAMMMMEEEE perlop - Perl operators and precedence SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS Perl operators have the following associativity and precedence, listed from highest precedence to lowest. Note that all operators borrowed from C keep the same precedence relationship with each other, even where C's precedence is slightly screwy. (This makes learning Perl easier for C folks.) With very few exceptions, these all operate on scalar values only, not array values. lllleeeefffftttt tttteeeerrrrmmmmssss aaaannnndddd lllliiiisssstttt ooooppppeeeerrrraaaattttoooorrrrssss ((((lllleeeeffffttttwwwwaaaarrrrdddd)))) lllleeeefffftttt ---->>>> nnnnoooonnnnaaaassssssssoooocccc ++++++++ -------- rrrriiiigggghhhhtttt ******** rrrriiiigggghhhhtttt !!!! ~~~~ \\\\ aaaannnndddd uuuunnnnaaaarrrryyyy ++++ aaaannnndddd ---- lllleeeefffftttt ====~~~~ !!!!~~~~ lllleeeefffftttt **** //// %%%% xxxx lllleeeefffftttt ++++ ---- .... lllleeeefffftttt <<<<<<<< >>>>>>>> nnnnoooonnnnaaaassssssssoooocccc nnnnaaaammmmeeeedddd uuuunnnnaaaarrrryyyy ooooppppeeeerrrraaaattttoooorrrrssss nnnnoooonnnnaaaassssssssoooocccc <<<< >>>> <<<<==== >>>>==== lllltttt ggggtttt lllleeee ggggeeee nnnnoooonnnnaaaassssssssoooocccc ======== !!!!==== <<<<====>>>> eeeeqqqq nnnneeee ccccmmmmpppp lllleeeefffftttt &&&& lllleeeefffftttt |||| ^^^^ lllleeeefffftttt &&&&&&&& lllleeeefffftttt |||||||| nnnnoooonnnnaaaassssssssoooocccc ........ rrrriiiigggghhhhtttt ????:::: rrrriiiigggghhhhtttt ==== ++++==== ----==== ****==== eeeettttcccc.... lllleeeefffftttt ,,,, ====>>>> nnnnoooonnnnaaaassssssssoooocccc lllliiiisssstttt ooooppppeeeerrrraaaattttoooorrrrssss ((((rrrriiiigggghhhhttttwwwwaaaarrrrdddd)))) rrrriiiigggghhhhtttt nnnnooootttt lllleeeefffftttt aaaannnndddd lllleeeefffftttt oooorrrr xxxxoooorrrr In the following sections, these operators are covered in precedence order. DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN TTTTeeeerrrrmmmmssss aaaannnndddd LLLLiiiisssstttt OOOOppppeeeerrrraaaattttoooorrrrssss ((((LLLLeeeeffffttttwwwwaaaarrrrdddd)))) Any TERM is of highest precedence of Perl. These includes variables, quote and quotelike operators, any expression in parentheses, and any function whose arguments are parenthesized. Actually, there aren't really functions in this sense, just list operators and unary operators behaving as functions because you put parentheses around the arguments. These are all documented in the _p_e_r_l_f_u_n_c manpage. If any list operator (_p_r_i_n_t_(_), etc.) or any unary operator (_c_h_d_i_r_(_), etc.) is followed by a left parenthesis as the 13/Feb/96 perl 5.002 with 1 PERLOP(1) User Contributed Perl Documentation PERLOP(1) next token, the operator and arguments within parentheses are taken to be of highest precedence, just like a normal function call. In the absence of parentheses, the precedence of list operators such as pppprrrriiiinnnntttt, ssssoooorrrrtttt, or cccchhhhmmmmoooodddd is either very high or very low depending on whether you look at the left side of operator or the right side of it. For example, in @@@@aaaarrrryyyy ==== ((((1111,,,, 3333,,,, ssssoooorrrrtttt 4444,,,, 2222))));;;; pppprrrriiiinnnntttt @@@@aaaarrrryyyy;;;; #### pppprrrriiiinnnnttttssss 1111333322224444 the commas on the right of the sort are evaluated before the sort, but the commas on the left are evaluated after. In other words, list operators tend to gobble up all the arguments that follow them, and then act like a simple TERM with regard to the preceding expression. Note that you have to be careful with parens: #### TTTThhhheeeesssseeee eeeevvvvaaaalllluuuuaaaatttteeee eeeexxxxiiiitttt bbbbeeeeffffoooorrrreeee ddddooooiiiinnnngggg tttthhhheeee pppprrrriiiinnnntttt:::: pppprrrriiiinnnntttt(((($$$$ffffoooooooo,,,, eeeexxxxiiiitttt))));;;; #### OOOObbbbvvvviiiioooouuuussssllllyyyy nnnnooootttt wwwwhhhhaaaatttt yyyyoooouuuu wwwwaaaannnntttt.... pppprrrriiiinnnntttt $$$$ffffoooooooo,,,, eeeexxxxiiiitttt;;;; #### NNNNoooorrrr iiiissss tttthhhhiiiissss.... #### TTTThhhheeeesssseeee ddddoooo tttthhhheeee pppprrrriiiinnnntttt bbbbeeeeffffoooorrrreeee eeeevvvvaaaalllluuuuaaaattttiiiinnnngggg eeeexxxxiiiitttt:::: ((((pppprrrriiiinnnntttt $$$$ffffoooooooo)))),,,, eeeexxxxiiiitttt;;;; #### TTTThhhhiiiissss iiiissss wwwwhhhhaaaatttt yyyyoooouuuu wwwwaaaannnntttt.... pppprrrriiiinnnntttt(((($$$$ffffoooooooo)))),,,, eeeexxxxiiiitttt;;;; #### OOOOrrrr tttthhhhiiiissss.... pppprrrriiiinnnntttt (((($$$$ffffoooooooo)))),,,, eeeexxxxiiiitttt;;;; #### OOOOrrrr eeeevvvveeeennnn tttthhhhiiiissss.... Also note that pppprrrriiiinnnntttt (((($$$$ffffoooooooo &&&& 222255555555)))) ++++ 1111,,,, """"\\\\nnnn"""";;;; probably doesn't do what you expect at first glance. See the section on _N_a_m_e_d _U_n_a_r_y _O_p_e_r_a_t_o_r_s for more discussion of this. Also parsed as terms are the ddddoooo {{{{}}}} and eeeevvvvaaaallll {{{{}}}} constructs, as well as subroutine and method calls, and the anonymous constructors [[[[]]]] and {{{{}}}}. See also the section on _Q_u_o_t_e _a_n_d _Q_u_o_t_e_l_i_k_e _O_p_e_r_a_t_o_r_s toward the end of this section, as well as the section on _I_/_O _O_p_e_r_a_t_o_r_s. TTTThhhheeee AAAArrrrrrrroooowwww OOOOppppeeeerrrraaaattttoooorrrr Just as in C and C++, "---->>>>" is an infix dereference operator. If the right side is either a [[[[............]]]] or {{{{............}}}} subscript, then the left side must be either a hard or symbolic reference to an array or hash (or a location capable of holding a hard reference, if it's an lvalue (assignable)). See the _p_e_r_l_r_e_f manpage. Otherwise, the right side is a method name or a simple 13/Feb/96 perl 5.002 with 2 PERLOP(1) User Contributed Perl Documentation PERLOP(1) scalar variable containing the method name, and the left side must either be an object (a blessed reference) or a class name (that is, a package name). See the _p_e_r_l_o_b_j manpage. AAAAuuuuttttooooiiiinnnnccccrrrreeeemmmmeeeennnntttt aaaannnndddd AAAAuuuuttttooooddddeeeeccccrrrreeeemmmmeeeennnntttt "++" and "--" work as in C. That is, if placed before a variable, they increment or decrement the variable before returning the value, and if placed after, increment or decrement the variable after returning the value. The autoincrement operator has a little extra built-in magic to it. If you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has only been used in string contexts since it was set, and has a value that is not null and matches the pattern ////^^^^[[[[aaaa----zzzzAAAA---- ZZZZ]]]]****[[[[0000----9999]]]]****$$$$////, the increment is done as a string, preserving each character within its range, with carry: pppprrrriiiinnnntttt ++++++++(((($$$$ffffoooooooo ==== ''''99999999''''))));;;; #### pppprrrriiiinnnnttttssss ''''111100000000'''' pppprrrriiiinnnntttt ++++++++(((($$$$ffffoooooooo ==== ''''aaaa0000''''))));;;; #### pppprrrriiiinnnnttttssss ''''aaaa1111'''' pppprrrriiiinnnntttt ++++++++(((($$$$ffffoooooooo ==== ''''AAAAzzzz''''))));;;; #### pppprrrriiiinnnnttttssss ''''BBBBaaaa'''' pppprrrriiiinnnntttt ++++++++(((($$$$ffffoooooooo ==== ''''zzzzzzzz''''))));;;; #### pppprrrriiiinnnnttttssss ''''aaaaaaaaaaaa'''' The autodecrement operator is not magical. EEEExxxxppppoooonnnneeeennnnttttiiiiaaaattttiiiioooonnnn Binary "**" is the exponentiation operator. Note that it binds even more tightly than unary minus, so -2**4 is -(2**4), not (-2)**4. (This is implemented using C's _p_o_w(3) function, which actually works on doubles internally.) SSSSyyyymmmmbbbboooolllliiiicccc UUUUnnnnaaaarrrryyyy OOOOppppeeeerrrraaaattttoooorrrrssss Unary "!" performs logical negation, i.e. "not". See also nnnnooootttt for a lower precedence version of this. Unary "-" performs arithmetic negation if the operand is numeric. If the operand is an identifier, a string consisting of a minus sign concatenated with the identifier is returned. Otherwise, if the string starts with a plus or minus, a string starting with the opposite sign is returned. One effect of these rules is that ----bbbbaaaarrrreeeewwwwoooorrrrdddd is equivalent to """"----bbbbaaaarrrreeeewwwwoooorrrrdddd"""". Unary "~" performs bitwise negation, i.e. 1's complement. Unary "+" has no effect whatsoever, even on strings. It is useful syntactically for separating a function name from a parenthesized expression that would otherwise be 13/Feb/96 perl 5.002 with 3 PERLOP(1) User Contributed Perl Documentation PERLOP(1) interpreted as the complete list of function arguments. (See examples above under the section on _L_i_s_t _O_p_e_r_a_t_o_r_s.) Unary "\" creates a reference to whatever follows it. See the _p_e_r_l_r_e_f manpage. Do not confuse this behavior with the behavior of backslash within a string, although both forms do convey the notion of protecting the next thing from interpretation. BBBBiiiinnnnddddiiiinnnngggg OOOOppppeeeerrrraaaattttoooorrrrssss Binary "=~" binds a scalar expression to a pattern match. Certain operations search or modify the string $$$$____ by default. This operator makes that kind of operation work on some other string. The right argument is a search pattern, substitution, or translation. The left argument is what is supposed to be searched, substituted, or translated instead of the default $$$$____. The return value indicates the success of the operation. (If the right argument is an expression rather than a search pattern, substitution, or translation, it is interpreted as a search pattern at run time. This is less efficient than an explicit search, since the pattern must be compiled every time the expression is evaluated--unless you've used ////oooo.) Binary "!~" is just like "=~" except the return value is negated in the logical sense. MMMMuuuullllttttiiiipppplllliiiiccccaaaattttiiiivvvveeee OOOOppppeeeerrrraaaattttoooorrrrssss Binary "*" multiplies two numbers. Binary "/" divides two numbers. Binary "%" computes the modulus of the two numbers. Binary "x" is the repetition operator. In a scalar context, it returns a string consisting of the left operand repeated the number of times specified by the right operand. In a list context, if the left operand is a list in parens, it repeats the list. pppprrrriiiinnnntttt ''''----'''' xxxx 88880000;;;; #### pppprrrriiiinnnntttt rrrroooowwww ooooffff ddddaaaasssshhhheeeessss pppprrrriiiinnnntttt """"\\\\tttt"""" xxxx (((($$$$ttttaaaabbbb////8888)))),,,, '''' '''' xxxx (((($$$$ttttaaaabbbb%%%%8888))));;;; #### ttttaaaabbbb oooovvvveeeerrrr @@@@oooonnnneeeessss ==== ((((1111)))) xxxx 88880000;;;; #### aaaa lllliiiisssstttt ooooffff 88880000 1111''''ssss @@@@oooonnnneeeessss ==== ((((5555)))) xxxx @@@@oooonnnneeeessss;;;; #### sssseeeetttt aaaallllllll eeeelllleeeemmmmeeeennnnttttssss ttttoooo 5555 13/Feb/96 perl 5.002 with 4 PERLOP(1) User Contributed Perl Documentation PERLOP(1) AAAAddddddddiiiittttiiiivvvveeee OOOOppppeeeerrrraaaattttoooorrrrssss Binary "+" returns the sum of two numbers. Binary "-" returns the difference of two numbers. Binary "." concatenates two strings. SSSShhhhiiiifffftttt OOOOppppeeeerrrraaaattttoooorrrrssss Binary "<<" returns the value of its left argument shifted left by the number of bits specified by the right argument. Arguments should be integers. Binary ">>" returns the value of its left argument shifted right by the number of bits specified by the right argument. Arguments should be integers. NNNNaaaammmmeeeedddd UUUUnnnnaaaarrrryyyy OOOOppppeeeerrrraaaattttoooorrrrssss The various named unary operators are treated as functions with one argument, with optional parentheses. These include the filetest operators, like ----ffff, ----MMMM, etc. See the _p_e_r_l_f_u_n_c manpage. If any list operator (_p_r_i_n_t_(_), etc.) or any unary operator (_c_h_d_i_r_(_), etc.) is followed by a left parenthesis as the next token, the operator and arguments within parentheses are taken to be of highest precedence, just like a normal function call. Examples: cccchhhhddddiiiirrrr $$$$ffffoooooooo |||||||| ddddiiiieeee;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) |||||||| ddddiiiieeee cccchhhhddddiiiirrrr(((($$$$ffffoooooooo)))) |||||||| ddddiiiieeee;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) |||||||| ddddiiiieeee cccchhhhddddiiiirrrr (((($$$$ffffoooooooo)))) |||||||| ddddiiiieeee;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) |||||||| ddddiiiieeee cccchhhhddddiiiirrrr ++++(((($$$$ffffoooooooo)))) |||||||| ddddiiiieeee;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) |||||||| ddddiiiieeee but, because * is higher precedence than ||: cccchhhhddddiiiirrrr $$$$ffffoooooooo **** 22220000;;;; #### cccchhhhddddiiiirrrr (((($$$$ffffoooooooo **** 22220000)))) cccchhhhddddiiiirrrr(((($$$$ffffoooooooo)))) **** 22220000;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) **** 22220000 cccchhhhddddiiiirrrr (((($$$$ffffoooooooo)))) **** 22220000;;;; #### ((((cccchhhhddddiiiirrrr $$$$ffffoooooooo)))) **** 22220000 cccchhhhddddiiiirrrr ++++(((($$$$ffffoooooooo)))) **** 22220000;;;; #### cccchhhhddddiiiirrrr (((($$$$ffffoooooooo **** 22220000)))) rrrraaaannnndddd 11110000 **** 22220000;;;; #### rrrraaaannnndddd ((((11110000 **** 22220000)))) rrrraaaannnndddd((((11110000)))) **** 22220000;;;; #### ((((rrrraaaannnndddd 11110000)))) **** 22220000 rrrraaaannnndddd ((((11110000)))) **** 22220000;;;; #### ((((rrrraaaannnndddd 11110000)))) **** 22220000 rrrraaaannnndddd ++++((((11110000)))) **** 22220000;;;; #### rrrraaaannnndddd ((((11110000 **** 22220000)))) See also the section on _L_i_s_t _O_p_e_r_a_t_o_r_s. RRRReeeellllaaaattttiiiioooonnnnaaaallll OOOOppppeeeerrrraaaattttoooorrrrssss Binary "<" returns true if the left argument is numerically less than the right argument. 13/Feb/96 perl 5.002 with 5 PERLOP(1) User Contributed Perl Documentation PERLOP(1) Binary ">" returns true if the left argument is numerically greater than the right argument. Binary "<=" returns true if the left argument is numerically less than or equal to the right argument. Binary ">=" returns true if the left argument is numerically greater than or equal to the right argument. Binary "lt" returns true if the left argument is stringwise less than the right argument. Binary "gt" returns true if the left argument is stringwise greater than the right argument. Binary "le" returns true if the left argument is stringwise less than or equal to the right argument. Binary "ge" returns true if the left argument is stringwise greater than or equal to the right argument. EEEEqqqquuuuaaaalllliiiittttyyyy OOOOppppeeeerrrraaaattttoooorrrrssss Binary "==" returns true if the left argument is numerically equal to the right argument. Binary "!=" returns true if the left argument is numerically not equal to the right argument. Binary "<=>" returns -1, 0, or 1 depending on whether the left argument is numerically less than, equal to, or greater than the right argument. Binary "eq" returns true if the left argument is stringwise equal to the right argument. Binary "ne" returns true if the left argument is stringwise not equal to the right argument. Binary "cmp" returns -1, 0, or 1 depending on whether the left argument is stringwise less than, equal to, or greater than the right argument. BBBBiiiittttwwwwiiiisssseeee AAAAnnnndddd Binary "&" returns its operators ANDed together bit by bit. BBBBiiiittttwwwwiiiisssseeee OOOOrrrr aaaannnndddd EEEExxxxcccclllluuuussssiiiivvvveeee OOOOrrrr Binary "|" returns its operators ORed together bit by bit. Binary "^" returns its operators XORed together bit by bit. 13/Feb/96 perl 5.002 with 6 PERLOP(1) User Contributed Perl Documentation PERLOP(1) CCCC----ssssttttyyyylllleeee LLLLooooggggiiiiccccaaaallll AAAAnnnndddd Binary "&&" performs a short-circuit logical AND operation. That is, if the left operand is false, the right operand is not even evaluated. Scalar or list context propagates down to the right operand if it is evaluated. CCCC----ssssttttyyyylllleeee LLLLooooggggiiiiccccaaaallll OOOOrrrr Binary "||" performs a short-circuit logical OR operation. That is, if the left operand is true, the right operand is not even evaluated. Scalar or list context propagates down to the right operand if it is evaluated. The |||||||| and &&&&&&&& operators differ from C's in that, rather than returning 0 or 1, they return the last value evaluated. Thus, a reasonably portable way to find out the home directory (assuming it's not "0") might be: $$$$hhhhoooommmmeeee ==== $$$$EEEENNNNVVVV{{{{''''HHHHOOOOMMMMEEEE''''}}}} |||||||| $$$$EEEENNNNVVVV{{{{''''LLLLOOOOGGGGDDDDIIIIRRRR''''}}}} |||||||| ((((ggggeeeettttppppwwwwuuuuiiiidddd(((($$$$<<<<))))))))[[[[7777]]]] |||||||| ddddiiiieeee """"YYYYoooouuuu''''rrrreeee hhhhoooommmmeeeelllleeeessssssss!!!!\\\\nnnn"""";;;; As more readable alternatives to &&&&&&&& and ||||||||, Perl provides "and" and "or" operators (see below). The short-circuit behavior is identical. The precedence of "and" and "or" is much lower, however, so that you can safely use them after a list operator without the need for parentheses: uuuunnnnlllliiiinnnnkkkk """"aaaallllpppphhhhaaaa"""",,,, """"bbbbeeeettttaaaa"""",,,, """"ggggaaaammmmmmmmaaaa"""" oooorrrr ggggrrrriiiippppeeee(((()))),,,, nnnneeeexxxxtttt LLLLIIIINNNNEEEE;;;; With the C-style operators that would have been written like this: uuuunnnnlllliiiinnnnkkkk((((""""aaaallllpppphhhhaaaa"""",,,, """"bbbbeeeettttaaaa"""",,,, """"ggggaaaammmmmmmmaaaa"""")))) |||||||| ((((ggggrrrriiiippppeeee(((()))),,,, nnnneeeexxxxtttt LLLLIIIINNNNEEEE))));;;; RRRRaaaannnnggggeeee OOOOppppeeeerrrraaaattttoooorrrr Binary ".." is the range operator, which is really two different operators depending on the context. In a list context, it returns an array of values counting (by ones) from the left value to the right value. This is useful for writing ffffoooorrrr ((((1111........11110000)))) loops and for doing slice operations on arrays. Be aware that under the current implementation, a temporary array is created, so you'll burn a lot of memory if you write something like this: ffffoooorrrr ((((1111 ........ 1111____000000000000____000000000000)))) {{{{ #### ccccooooddddeeee }}}} 13/Feb/96 perl 5.002 with 7 PERLOP(1) User Contributed Perl Documentation PERLOP(1) In a scalar context, ".." returns a boolean value. The operator is bistable, like a flip-flop, and emulates the line-range (comma) operator of sssseeeedddd, aaaawwwwkkkk, and various editors. Each ".." operator maintains its own boolean state. It is false as long as its left operand is false. Once the left operand is true, the range operator stays true until the right operand is true, _A_F_T_E_R which the range operator becomes false again. (It doesn't become false till the next time the range operator is evaluated. It can test the right operand and become false on the same evaluation it became true (as in aaaawwwwkkkk), but it still returns true once. If you don't want it to test the right operand till the next evaluation (as in sssseeeedddd), use three dots ("...") instead of two.) The right operand is not evaluated while the operator is in the "false" state, and the left operand is not evaluated while the operator is in the "true" state. The precedence is a little lower than || and &&. The value returned is either the null string for false, or a sequence number (beginning with 1) for true. The sequence number is reset for each range encountered. The final sequence number in a range has the string "E0" appended to it, which doesn't affect its numeric value, but gives you something to search for if you want to exclude the endpoint. You can exclude the beginning point by waiting for the sequence number to be greater than 1. If either operand of scalar ".." is a numeric literal, that operand is implicitly compared to the $$$$.... variable, the current line number. Examples: As a scalar operator: iiiiffff ((((111100001111 ........ 222200000000)))) {{{{ pppprrrriiiinnnntttt;;;; }}}} #### pppprrrriiiinnnntttt 2222nnnndddd hhhhuuuunnnnddddrrrreeeedddd lllliiiinnnneeeessss nnnneeeexxxxtttt lllliiiinnnneeee iiiiffff ((((1111 ........ ////^^^^$$$$////))));;;; #### sssskkkkiiiipppp hhhheeeeaaaaddddeeeerrrr lllliiiinnnneeeessss ssss////^^^^////>>>> //// iiiiffff ((((////^^^^$$$$//// ........ eeeeooooffff(((())))))));;;; #### qqqquuuuooootttteeee bbbbooooddddyyyy As a list operator: ffffoooorrrr ((((111100001111 ........ 222200000000)))) {{{{ pppprrrriiiinnnntttt;;;; }}}} #### pppprrrriiiinnnntttt $$$$____ 111100000000 ttttiiiimmmmeeeessss @@@@ffffoooooooo ==== @@@@ffffoooooooo[[[[$$$$[[[[ ........ $$$$####ffffoooooooo]]]];;;; #### aaaannnn eeeexxxxppppeeeennnnssssiiiivvvveeee nnnnoooo----oooopppp @@@@ffffoooooooo ==== @@@@ffffoooooooo[[[[$$$$####ffffoooooooo----4444 ........ $$$$####ffffoooooooo]]]];;;; #### sssslllliiiicccceeee llllaaaasssstttt 5555 iiiitttteeeemmmmssss The range operator (in a list context) makes use of the magical autoincrement algorithm if the operaands are strings. You can say @@@@aaaallllpppphhhhaaaabbbbeeeetttt ==== ((((''''AAAA'''' ........ ''''ZZZZ''''))));;;; to get all the letters of the alphabet, or $$$$hhhheeeexxxxddddiiiiggggiiiitttt ==== ((((0000 ........ 9999,,,, ''''aaaa'''' ........ ''''ffff''''))))[[[[$$$$nnnnuuuummmm &&&& 11115555]]]];;;; to get a hexadecimal digit, or @@@@zzzz2222 ==== ((((''''00001111'''' ........ ''''33331111''''))));;;; pppprrrriiiinnnntttt $$$$zzzz2222[[[[$$$$mmmmddddaaaayyyy]]]];;;; 13/Feb/96 perl 5.002 with 8 PERLOP(1) User Contributed Perl Documentation PERLOP(1) to get dates with leading zeros. If the final value specified is not in the sequence that the magical increment would produce, the sequence goes until the next value would be longer than the final value specified. CCCCoooonnnnddddiiiittttiiiioooonnnnaaaallll OOOOppppeeeerrrraaaattttoooorrrr Ternary "?:" is the conditional operator, just as in C. It works much like an if-then-else. If the argument before the ? is true, the argument before the : is returned, otherwise the argument after the : is returned. For example: pppprrrriiiinnnnttttffff """"IIII hhhhaaaavvvveeee %%%%dddd ddddoooogggg%%%%ssss....\\\\nnnn"""",,,, $$$$nnnn,,,, (((($$$$nnnn ======== 1111)))) ???? '''''''' :::: """"ssss"""";;;; Scalar or list context propagates downward into the 2nd or 3rd argument, whichever is selected. $$$$aaaa ==== $$$$ooookkkk ???? $$$$bbbb :::: $$$$cccc;;;; #### ggggeeeetttt aaaa ssssccccaaaallllaaaarrrr @@@@aaaa ==== $$$$ooookkkk ???? @@@@bbbb :::: @@@@cccc;;;; #### ggggeeeetttt aaaannnn aaaarrrrrrrraaaayyyy $$$$aaaa ==== $$$$ooookkkk ???? @@@@bbbb :::: @@@@cccc;;;; #### ooooooooppppssss,,,, tttthhhhaaaatttt''''ssss jjjjuuuusssstttt aaaa ccccoooouuuunnnntttt!!!! The operator may be assigned to if both the 2nd and 3rd arguments are legal lvalues (meaning that you can assign to them): (((($$$$aaaa____oooorrrr____bbbb ???? $$$$aaaa :::: $$$$bbbb)))) ==== $$$$cccc;;;; This is not necessarily guaranteed to contribute to the readability of your program. AAAAssssssssiiiiggggnnnnmmmmeeeennnntttt OOOOppppeeeerrrraaaattttoooorrrrssss "=" is the ordinary assignment operator. Assignment operators work as in C. That is, $$$$aaaa ++++==== 2222;;;; is equivalent to $$$$aaaa ==== $$$$aaaa ++++ 2222;;;; although without duplicating any side effects that dereferencing the lvalue might trigger, such as from _t_i_e_(_). Other assignment operators work similarly. The following are recognized: ********==== ++++==== ****==== &&&&==== <<<<<<<<==== &&&&&&&&==== ----==== ////==== ||||==== >>>>>>>>==== ||||||||==== ....==== %%%%==== ^^^^==== xxxx==== 13/Feb/96 perl 5.002 with 9 PERLOP(1) User Contributed Perl Documentation PERLOP(1) Note that while these are grouped by family, they all have the precedence of assignment. Unlike in C, the assignment operator produces a valid lvalue. Modifying an assignment is equivalent to doing the assignment and then modifying the variable that was assigned to. This is useful for modifying a copy of something, like this: (((($$$$ttttmmmmpppp ==== $$$$gggglllloooobbbbaaaallll)))) ====~~~~ ttttrrrr [[[[AAAA----ZZZZ]]]] [[[[aaaa----zzzz]]]];;;; Likewise, (((($$$$aaaa ++++==== 2222)))) ****==== 3333;;;; is equivalent to $$$$aaaa ++++==== 2222;;;; $$$$aaaa ****==== 3333;;;; CCCCoooommmmmmmmaaaa OOOOppppeeeerrrraaaattttoooorrrr Binary "," is the comma operator. In a scalar context it evaluates its left argument, throws that value away, then evaluates its right argument and returns that value. This is just like C's comma operator. In a list context, it's just the list argument separator, and inserts both its arguments into the list. The => digraph is mostly just a synonym for the comma operator. It's useful for documenting arguments that come in pairs. As of release 5.001, it also forces any word to the left of it to be interpreted as a string. LLLLiiiisssstttt OOOOppppeeeerrrraaaattttoooorrrrssss ((((RRRRiiiigggghhhhttttwwwwaaaarrrrdddd)))) On the right side of a list operator, it has very low precedence, such that it controls all comma-separated expressions found there. The only operators with lower precedence are the logical operators "and", "or", and "not", which may be used to evaluate calls to list operators without the need for extra parentheses: ooooppppeeeennnn HHHHAAAANNNNDDDDLLLLEEEE,,,, """"ffffiiiilllleeeennnnaaaammmmeeee"""" oooorrrr ddddiiiieeee """"CCCCaaaannnn''''tttt ooooppppeeeennnn:::: $$$$!!!!\\\\nnnn"""";;;; See also discussion of list operators in the section on _L_i_s_t _O_p_e_r_a_t_o_r_s _(_L_e_f_t_w_a_r_d_). 13/Feb/96 perl 5.002 with 10 PERLOP(1) User Contributed Perl Documentation PERLOP(1) LLLLooooggggiiiiccccaaaallll NNNNooootttt Unary "not" returns the logical negation of the expression to its right. It's the equivalent of "!" except for the very low precedence. LLLLooooggggiiiiccccaaaallll AAAAnnnndddd Binary "and" returns the logical conjunction of the two surrounding expressions. It's equivalent to && except for the very low precedence. This means that it short- circuits: i.e. the right expression is evaluated only if the left expression is true. LLLLooooggggiiiiccccaaaallll oooorrrr aaaannnndddd EEEExxxxcccclllluuuussssiiiivvvveeee OOOOrrrr Binary "or" returns the logical disjunction of the two surrounding expressions. It's equivalent to || except for the very low precedence. This means that it short- circuits: i.e. the right expression is evaluated only if the left expression is false. Binary "xor" returns the exclusive-OR of the two surrounding expressions. It cannot short circuit, of course. CCCC OOOOppppeeeerrrraaaattttoooorrrrssss MMMMiiiissssssssiiiinnnngggg FFFFrrrroooommmm PPPPeeeerrrrllll Here is what C has that Perl doesn't: unary & Address-of operator. (But see the "\" operator for taking a reference.) unary * Dereference-address operator. (Perl's prefix dereferencing operators are typed: $, @, %, and &.) (TYPE) Type casting operator. QQQQuuuuooootttteeee aaaannnndddd QQQQuuuuooootttteeeelllliiiikkkkeeee OOOOppppeeeerrrraaaattttoooorrrrssss While we usually think of quotes as literal values, in Perl they function as operators, providing various kinds of interpolating and pattern matching capabilities. Perl provides customary quote characters for these behaviors, but also provides a way for you to choose your quote character for any of them. In the following table, a {{{{}}}} represents any pair of delimiters you choose. Non- bracketing delimiters use the same character fore and aft, but the 4 sorts of brackets (round, angle, square, curly) will all nest. 13/Feb/96 perl 5.002 with 11 PERLOP(1) User Contributed Perl Documentation PERLOP(1) CCCCuuuussssttttoooommmmaaaarrrryyyy GGGGeeeennnneeeerrrriiiicccc MMMMeeeeaaaannnniiiinnnngggg IIIInnnntttteeeerrrrppppoooollllaaaatttteeeessss '''''''' qqqq{{{{}}}} LLLLiiiitttteeeerrrraaaallll nnnnoooo """""""" qqqqqqqq{{{{}}}} LLLLiiiitttteeeerrrraaaallll yyyyeeeessss ```````` qqqqxxxx{{{{}}}} CCCCoooommmmmmmmaaaannnndddd yyyyeeeessss qqqqwwww{{{{}}}} WWWWoooorrrrdddd lllliiiisssstttt nnnnoooo //////// mmmm{{{{}}}} PPPPaaaatttttttteeeerrrrnnnn mmmmaaaattttcccchhhh yyyyeeeessss ssss{{{{}}}}{{{{}}}} SSSSuuuubbbbssssttttiiiittttuuuuttttiiiioooonnnn yyyyeeeessss ttttrrrr{{{{}}}}{{{{}}}} TTTTrrrraaaannnnssssllllaaaattttiiiioooonnnn nnnnoooo For constructs that do interpolation, variables beginning with "$$$$" or "@@@@" are interpolated, as are the following sequences: \\\\tttt ttttaaaabbbb \\\\nnnn nnnneeeewwwwlllliiiinnnneeee \\\\rrrr rrrreeeettttuuuurrrrnnnn \\\\ffff ffffoooorrrrmmmm ffffeeeeeeeedddd \\\\bbbb bbbbaaaacccckkkkssssppppaaaacccceeee \\\\aaaa aaaallllaaaarrrrmmmm ((((bbbbeeeellllllll)))) \\\\eeee eeeessssccccaaaappppeeee \\\\000033333333 ooooccccttttaaaallll cccchhhhaaaarrrr \\\\xxxx1111bbbb hhhheeeexxxx cccchhhhaaaarrrr \\\\cccc[[[[ ccccoooonnnnttttrrrroooollll cccchhhhaaaarrrr \\\\llll lllloooowwwweeeerrrrccccaaaasssseeee nnnneeeexxxxtttt cccchhhhaaaarrrr \\\\uuuu uuuuppppppppeeeerrrrccccaaaasssseeee nnnneeeexxxxtttt cccchhhhaaaarrrr \\\\LLLL lllloooowwwweeeerrrrccccaaaasssseeee ttttiiiillllllll \\\\EEEE \\\\UUUU uuuuppppppppeeeerrrrccccaaaasssseeee ttttiiiillllllll \\\\EEEE \\\\EEEE eeeennnndddd ccccaaaasssseeee mmmmooooddddiiiiffffiiiiccccaaaattttiiiioooonnnn \\\\QQQQ qqqquuuuooootttteeee rrrreeeeggggeeeexxxxpppp mmmmeeeettttaaaacccchhhhaaaarrrraaaacccctttteeeerrrrssss ttttiiiillllllll \\\\EEEE Patterns are subject to an additional level of interpretation as a regular expression. This is done as a second pass, after variables are interpolated, so that regular expressions may be incorporated into the pattern from the variables. If this is not what you want, use \\\\QQQQ to interpolate a variable literally. Apart from the above, there are no multiple levels of interpolation. In particular, contrary to the expectations of shell programmers, backquotes do _N_O_T interpolate within double quotes, nor do single quotes impede evaluation of variables when used within double quotes. RRRReeeeggggeeeexxxxpppp QQQQuuuuooootttteeeelllliiiikkkkeeee OOOOppppeeeerrrraaaattttoooorrrrssss Here are the quotelike operators that apply to pattern matching and related activities. ?PATTERN? This is just like the ////ppppaaaatttttttteeeerrrrnnnn//// search, except that it matches only once between calls to the _r_e_s_e_t_(_) operator. This is a useful optimization when you only want to see the first occurrence of 13/Feb/96 perl 5.002 with 12 PERLOP(1) User Contributed Perl Documentation PERLOP(1) something in each file of a set of files, for instance. Only ???????? patterns local to the current package are reset. This usage is vaguely deprecated, and may be removed in some future version of Perl. m/PATTERN/gimosx /PATTERN/gimosx Searches a string for a pattern match, and in a scalar context returns true (1) or false (''). If no string is specified via the ====~~~~ or !!!!~~~~ operator, the $$$$____ string is searched. (The string specified with ====~~~~ need not be an lvalue--it may be the result of an expression evaluation, but remember the ====~~~~ binds rather tightly.) See also the _p_e_r_l_r_e manpage. Options are: gggg MMMMaaaattttcccchhhh gggglllloooobbbbaaaallllllllyyyy,,,, iiii....eeee.... ffffiiiinnnndddd aaaallllllll ooooccccccccuuuurrrrrrrreeeennnncccceeeessss.... iiii DDDDoooo ccccaaaasssseeee----iiiinnnnsssseeeennnnssssiiiittttiiiivvvveeee ppppaaaatttttttteeeerrrrnnnn mmmmaaaattttcccchhhhiiiinnnngggg.... mmmm TTTTrrrreeeeaaaatttt ssssttttrrrriiiinnnngggg aaaassss mmmmuuuullllttttiiiipppplllleeee lllliiiinnnneeeessss.... oooo OOOOnnnnllllyyyy ccccoooommmmppppiiiilllleeee ppppaaaatttttttteeeerrrrnnnn oooonnnncccceeee.... ssss TTTTrrrreeeeaaaatttt ssssttttrrrriiiinnnngggg aaaassss ssssiiiinnnngggglllleeee lllliiiinnnneeee.... xxxx UUUUsssseeee eeeexxxxtttteeeennnnddddeeeedddd rrrreeeegggguuuullllaaaarrrr eeeexxxxpppprrrreeeessssssssiiiioooonnnnssss.... If "/" is the delimiter then the initial mmmm is optional. With the mmmm you can use any pair of non- alphanumeric, non-whitespace characters as delimiters. This is particularly useful for matching Unix path names that contain "/", to avoid LTS (leaning toothpick syndrome). PATTERN may contain variables, which will be interpolated (and the pattern recompiled) every time the pattern search is evaluated. (Note that $$$$)))) and $$$$|||| might not be interpolated because they look like end-of-string tests.) If you want such a pattern to be compiled only once, add a ////oooo after the trailing delimiter. This avoids expensive run-time recompilations, and is useful when the value you are interpolating won't change over the life of the script. However, mentioning ////oooo constitutes a promise that you won't change the variables in the pattern. If you change them, Perl won't even notice. If the PATTERN evaluates to a null string, the last successfully executed regular expression is used instead. If used in a context that requires a list value, a 13/Feb/96 perl 5.002 with 13 PERLOP(1) User Contributed Perl Documentation PERLOP(1) pattern match returns a list consisting of the subexpressions matched by the parentheses in the pattern, i.e. ($1, $$$$2222, $$$$3333...). (Note that here $$$$1111 etc. are also set, and that this differs from Perl 4's behavior.) If the match fails, a null array is returned. If the match succeeds, but there were no parentheses, a list value of (1) is returned. Examples: ooooppppeeeennnn((((TTTTTTTTYYYY,,,, ''''////ddddeeeevvvv////ttttttttyyyy''''))));;;; <<<<TTTTTTTTYYYY>>>> ====~~~~ ////^^^^yyyy////iiii &&&&&&&& ffffoooooooo(((())));;;; #### ddddoooo ffffoooooooo iiiiffff ddddeeeessssiiiirrrreeeedddd iiiiffff ((((////VVVVeeeerrrrssssiiiioooonnnn:::: ****(((([[[[0000----9999....]]]]****))))////)))) {{{{ $$$$vvvveeeerrrrssssiiiioooonnnn ==== $$$$1111;;;; }}}} nnnneeeexxxxtttt iiiiffff mmmm####^^^^////uuuussssrrrr////ssssppppoooooooollll////uuuuuuuuccccpppp####;;;; #### ppppoooooooorrrr mmmmaaaannnn''''ssss ggggrrrreeeepppp $$$$aaaarrrrgggg ==== sssshhhhiiiifffftttt;;;; wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{ pppprrrriiiinnnntttt iiiiffff ////$$$$aaaarrrrgggg////oooo;;;; #### ccccoooommmmppppiiiilllleeee oooonnnnllllyyyy oooonnnncccceeee }}}} iiiiffff (((((((($$$$FFFF1111,,,, $$$$FFFF2222,,,, $$$$EEEEttttcccc)))) ==== (((($$$$ffffoooooooo ====~~~~ ////^^^^((((\\\\SSSS++++))))\\\\ssss++++((((\\\\SSSS++++))))\\\\ssss****((((....****))))////)))))))) This last example splits $$$$ffffoooooooo into the first two words and the remainder of the line, and assigns those three fields to $$$$FFFF1111, $$$$FFFF2222 and $$$$EEEEttttcccc. The conditional is true if any variables were assigned, i.e. if the pattern matched. The ////gggg modifier specifies global pattern matching--that is, matching as many times as possible within the string. How it behaves depends on the context. In a list context, it returns a list of all the substrings matched by all the parentheses in the regular expression. If there are no parentheses, it returns a list of all the matched strings, as if there were parentheses around the whole pattern. In a scalar context, mmmm////////gggg iterates through the string, returning TRUE each time it matches, and FALSE when it eventually runs out of matches. (In other words, it remembers where it left off last time and restarts the search at that point. You can actually find the current match position of a string using the _p_o_s_(_) function--see the _p_e_r_l_f_u_n_c manpage.) If you modify the string in any way, the match position is reset to the beginning. Examples: 13/Feb/96 perl 5.002 with 14 PERLOP(1) User Contributed Perl Documentation PERLOP(1) #### lllliiiisssstttt ccccoooonnnntttteeeexxxxtttt (((($$$$oooonnnneeee,,,,$$$$ffffiiiivvvveeee,,,,$$$$ffffiiiifffftttteeeeeeeennnn)))) ==== ((((````uuuuppppttttiiiimmmmeeee```` ====~~~~ ////((((\\\\dddd++++\\\\....\\\\dddd++++))))////gggg))));;;; #### ssssccccaaaallllaaaarrrr ccccoooonnnntttteeeexxxxtttt $$$$//// ==== """""""";;;; $$$$**** ==== 1111;;;; #### $$$$**** ddddeeeepppprrrreeeeccccaaaatttteeeedddd iiiinnnn PPPPeeeerrrrllll 5555 wwwwhhhhiiiilllleeee (((($$$$ppppaaaarrrraaaaggggrrrraaaapppphhhh ==== <<<<>>>>)))) {{{{ wwwwhhhhiiiilllleeee (((($$$$ppppaaaarrrraaaaggggrrrraaaapppphhhh ====~~~~ ////[[[[aaaa----zzzz]]]][[[[''''""""))))]]]]****[[[[....!!!!????]]]]++++[[[[''''""""))))]]]]****\\\\ssss////gggg)))) {{{{ $$$$sssseeeennnntttteeeennnncccceeeessss++++++++;;;; }}}} }}}} pppprrrriiiinnnntttt """"$$$$sssseeeennnntttteeeennnncccceeeessss\\\\nnnn"""";;;; q/STRING/ ''''SSSSTTTTRRRRIIIINNNNGGGG'''' A single-quoted, literal string. Backslashes are ignored, unless followed by the delimiter or another backslash, in which case the delimiter or backslash is interpolated. $$$$ffffoooooooo ==== qqqq!!!!IIII ssssaaaaiiiidddd,,,, """"YYYYoooouuuu ssssaaaaiiiidddd,,,, ''''SSSShhhheeee ssssaaaaiiiidddd iiiitttt....''''""""!!!!;;;; $$$$bbbbaaaarrrr ==== qqqq((((''''TTTThhhhiiiissss iiiissss iiiitttt....''''))));;;; qq/STRING/ "STRING" A double-quoted, interpolated string. $$$$____ ....==== qqqqqqqq ((((************ TTTThhhheeee pppprrrreeeevvvviiiioooouuuussss lllliiiinnnneeee ccccoooonnnnttttaaaaiiiinnnnssss tttthhhheeee nnnnaaaauuuugggghhhhttttyyyy wwwwoooorrrrdddd """"$$$$1111""""....\\\\nnnn)))) iiiiffff ////((((ttttccccllll||||rrrreeeexxxxxxxx||||ppppyyyytttthhhhoooonnnn))))////;;;; #### ::::----)))) qx/STRING/ `STRING` A string which is interpolated and then executed as a system command. The collected standard output of the command is returned. In scalar context, it comes back as a single (potentially multi-line) string. In list context, returns a list of lines (however you've defined lines with $/ or $$$$IIIINNNNPPPPUUUUTTTT____RRRREEEECCCCOOOORRRRDDDD____SSSSEEEEPPPPAAAARRRRAAAATTTTOOOORRRR). $$$$ttttooooddddaaaayyyy ==== qqqqxxxx{{{{ ddddaaaatttteeee }}}};;;; See the section on _I_/_O _O_p_e_r_a_t_o_r_s for more discussion. qw/STRING/ Returns a list of the words extracted out of STRING, using embedded whitespace as the word 13/Feb/96 perl 5.002 with 15 PERLOP(1) User Contributed Perl Documentation PERLOP(1) delimiters. It is exactly equivalent to sssspppplllliiiitttt(((('''' '''',,,, qqqq////SSSSTTTTRRRRIIIINNNNGGGG////))));;;; Some frequently seen examples: uuuusssseeee PPPPOOOOSSSSIIIIXXXX qqqqwwww(((( sssseeeettttllllooooccccaaaalllleeee llllooooccccaaaalllleeeeccccoooonnnnvvvv )))) @@@@EEEEXXXXPPPPOOOORRRRTTTT ==== qqqqwwww(((( ffffoooooooo bbbbaaaarrrr bbbbaaaazzzz ))));;;; s/PATTERN/REPLACEMENT/egimosx Searches a string for a pattern, and if found, replaces that pattern with the replacement text and returns the number of substitutions made. Otherwise it returns false (0). If no string is specified via the ====~~~~ or !!!!~~~~ operator, the $$$$____ variable is searched and modified. (The string specified with ====~~~~ must be a scalar variable, an array element, a hash element, or an assignment to one of those, i.e. an lvalue.) If the delimiter chosen is single quote, no variable interpolation is done on either the PATTERN or the REPLACEMENT. Otherwise, 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. If you only want the pattern compiled once the first time the variable is interpolated, use the ////oooo option. If the pattern evaluates to a null string, the last successfully executed regular expression is used instead. See the _p_e_r_l_r_e manpage for further explanation on these. Options are: eeee EEEEvvvvaaaalllluuuuaaaatttteeee tttthhhheeee rrrriiiigggghhhhtttt ssssiiiiddddeeee aaaassss aaaannnn eeeexxxxpppprrrreeeessssssssiiiioooonnnn.... gggg RRRReeeeppppllllaaaacccceeee gggglllloooobbbbaaaallllllllyyyy,,,, iiii....eeee.... aaaallllllll ooooccccccccuuuurrrrrrrreeeennnncccceeeessss.... iiii DDDDoooo ccccaaaasssseeee----iiiinnnnsssseeeennnnssssiiiittttiiiivvvveeee ppppaaaatttttttteeeerrrrnnnn mmmmaaaattttcccchhhhiiiinnnngggg.... mmmm TTTTrrrreeeeaaaatttt ssssttttrrrriiiinnnngggg aaaassss mmmmuuuullllttttiiiipppplllleeee lllliiiinnnneeeessss.... oooo OOOOnnnnllllyyyy ccccoooommmmppppiiiilllleeee ppppaaaatttttttteeeerrrrnnnn oooonnnncccceeee.... ssss TTTTrrrreeeeaaaatttt ssssttttrrrriiiinnnngggg aaaassss ssssiiiinnnngggglllleeee lllliiiinnnneeee.... xxxx UUUUsssseeee eeeexxxxtttteeeennnnddddeeeedddd rrrreeeegggguuuullllaaaarrrr eeeexxxxpppprrrreeeessssssssiiiioooonnnnssss.... Any non-alphanumeric, non-whitespace delimiter may replace the slashes. If single quotes are used, no interpretation is done on the replacement string (the ////eeee modifier overrides this, however). If backquotes are used, the replacement string is a command to execute whose output will be used as the actual replacement text. If the PATTERN is delimited by bracketing quotes, the REPLACEMENT has its own pair of quotes, which may or may not 13/Feb/96 perl 5.002 with 16 PERLOP(1) User Contributed Perl Documentation PERLOP(1) be bracketing quotes, e.g. ssss((((ffffoooooooo))))((((bbbbaaaarrrr)))) or ssss<<<<ffffoooooooo>>>>////bbbbaaaarrrr////. A ////eeee will cause the replacement portion to be interpreter as a full-fledged Perl expression and _e_v_a_l_(_)ed right then and there. It is, however, syntax checked at compile-time. Examples: ssss////\\\\bbbbggggrrrreeeeeeeennnn\\\\bbbb////mmmmaaaauuuuvvvveeee////gggg;;;; #### ddddoooonnnn''''tttt cccchhhhaaaannnnggggeeee wwwwiiiinnnntttteeeerrrrggggrrrreeeeeeeennnn $$$$ppppaaaatttthhhh ====~~~~ ssss||||////uuuussssrrrr////bbbbiiiinnnn||||////uuuussssrrrr////llllooooccccaaaallll////bbbbiiiinnnn||||;;;; ssss////LLLLooooggggiiiinnnn:::: $$$$ffffoooooooo////LLLLooooggggiiiinnnn:::: $$$$bbbbaaaarrrr////;;;; #### rrrruuuunnnn----ttttiiiimmmmeeee ppppaaaatttttttteeeerrrrnnnn (((($$$$ffffoooooooo ==== $$$$bbbbaaaarrrr)))) ====~~~~ ssss////tttthhhhiiiissss////tttthhhhaaaatttt////;;;; $$$$ccccoooouuuunnnntttt ==== (((($$$$ppppaaaarrrraaaaggggrrrraaaapppphhhh ====~~~~ ssss////MMMMiiiisssstttteeeerrrr\\\\bbbb////MMMMrrrr....////gggg))));;;; $$$$____ ==== ''''aaaabbbbcccc111122223333xxxxyyyyzzzz'''';;;; ssss////\\\\dddd++++////$$$$&&&&****2222////eeee;;;; #### yyyyiiiieeeellllddddssss ''''aaaabbbbcccc222244446666xxxxyyyyzzzz'''' ssss////\\\\dddd++++////sssspppprrrriiiinnnnttttffff((((""""%%%%5555dddd"""",,,,$$$$&&&&))))////eeee;;;; #### yyyyiiiieeeellllddddssss ''''aaaabbbbcccc 222244446666xxxxyyyyzzzz'''' ssss////\\\\wwww////$$$$&&&& xxxx 2222////eeeegggg;;;; #### yyyyiiiieeeellllddddssss ''''aaaaaaaabbbbbbbbcccccccc 222222224444444466666666xxxxxxxxyyyyyyyyzzzzzzzz'''' ssss////%%%%((((....))))////$$$$ppppeeeerrrrcccceeeennnntttt{{{{$$$$1111}}}}////gggg;;;; #### cccchhhhaaaannnnggggeeee ppppeeeerrrrcccceeeennnntttt eeeessssccccaaaappppeeeessss;;;; nnnnoooo ////eeee ssss////%%%%((((....))))////$$$$ppppeeeerrrrcccceeeennnntttt{{{{$$$$1111}}}} |||||||| $$$$&&&&////ggggeeee;;;; #### eeeexxxxpppprrrr nnnnoooowwww,,,, ssssoooo ////eeee ssss////^^^^====((((\\\\wwww++++))))////&&&&ppppoooodddd(((($$$$1111))))////ggggeeee;;;; #### uuuusssseeee ffffuuuunnnnccccttttiiiioooonnnn ccccaaaallllllll #### ////eeee''''ssss ccccaaaannnn eeeevvvveeeennnn nnnneeeesssstttt;;;; tttthhhhiiiissss wwwwiiiillllllll eeeexxxxppppaaaannnndddd #### ssssiiiimmmmpppplllleeee eeeemmmmbbbbeeeeddddddddeeeedddd vvvvaaaarrrriiiiaaaabbbblllleeeessss iiiinnnn $$$$____ ssss////((((\\\\$$$$\\\\wwww++++))))////$$$$1111////eeeeeeeegggg;;;; #### DDDDeeeelllleeeetttteeee CCCC ccccoooommmmmmmmeeeennnnttttssss.... $$$$pppprrrrooooggggrrrraaaammmm ====~~~~ ssss {{{{ ////\\\\**** #### MMMMaaaattttcccchhhh tttthhhheeee ooooppppeeeennnniiiinnnngggg ddddeeeelllliiiimmmmiiiitttteeeerrrr.... ....****???? #### MMMMaaaattttcccchhhh aaaa mmmmiiiinnnniiiimmmmaaaallll nnnnuuuummmmbbbbeeeerrrr ooooffff cccchhhhaaaarrrraaaacccctttteeeerrrrssss.... \\\\****//// #### MMMMaaaattttcccchhhh tttthhhheeee cccclllloooossssiiiinnnngggg ddddeeeelllliiiimmmmiiiitttteeeerrrr.... }}}} [[[[]]]]ggggssssxxxx;;;; ssss////^^^^\\\\ssss****((((....****????))))\\\\ssss****$$$$////$$$$1111////;;;; #### ttttrrrriiiimmmm wwwwhhhhiiiitttteeee ssssppppaaaacccceeee ssss////(((([[[[^^^^ ]]]]****)))) ****(((([[[[^^^^ ]]]]****))))////$$$$2222 $$$$1111////;;;; #### rrrreeeevvvveeeerrrrsssseeee 1111sssstttt ttttwwwwoooo ffffiiiieeeellllddddssss Note the use of $ instead of \ in the last example. Unlike sssseeeedddd, we only use the \<_d_i_g_i_t> form in the left hand side. Anywhere else it's $<_d_i_g_i_t>. Occasionally, you can't just use a ////gggg to get all the changes to occur. Here are two common cases: #### ppppuuuutttt ccccoooommmmmmmmaaaassss iiiinnnn tttthhhheeee rrrriiiigggghhhhtttt ppppllllaaaacccceeeessss iiiinnnn aaaannnn iiiinnnntttteeeeggggeeeerrrr 1111 wwwwhhhhiiiilllleeee ssss////((((....****\\\\dddd))))((((\\\\dddd\\\\dddd\\\\dddd))))////$$$$1111,,,,$$$$2222////gggg;;;; #### ppppeeeerrrrllll4444 1111 wwwwhhhhiiiilllleeee ssss////((((\\\\dddd))))((((\\\\dddd\\\\dddd\\\\dddd))))((((????!!!!\\\\dddd))))////$$$$1111,,,,$$$$2222////gggg;;;; #### ppppeeeerrrrllll5555 13/Feb/96 perl 5.002 with 17 PERLOP(1) User Contributed Perl Documentation PERLOP(1) #### eeeexxxxppppaaaannnndddd ttttaaaabbbbssss ttttoooo 8888----ccccoooolllluuuummmmnnnn ssssppppaaaacccciiiinnnngggg 1111 wwwwhhhhiiiilllleeee ssss////\\\\tttt++++////'''' '''' xxxx ((((lllleeeennnnggggtttthhhh(((($$$$&&&&))))****8888 ---- lllleeeennnnggggtttthhhh(((($$$$````))))%%%%8888))))////eeee;;;; tr/SEARCHLIST/REPLACEMENTLIST/cds y/SEARCHLIST/REPLACEMENTLIST/cds Translates all occurrences of the characters found in the search list with the corresponding character in the replacement list. It returns the number of characters replaced or deleted. If no string is specified via the =~ or !~ operator, the $$$$____ string is translated. (The string specified with =~ must be a scalar variable, an array element, or an assignment to one of those, i.e. an lvalue.) For sssseeeedddd devotees, yyyy is provided as a synonym for ttttrrrr. If the SEARCHLIST is delimited by bracketing quotes, the REPLACEMENTLIST has its own pair of quotes, which may or may not be bracketing quotes, e.g. ttttrrrr[[[[AAAA----ZZZZ]]]][[[[aaaa----zzzz]]]] or ttttrrrr((((++++----****////))))////AAAABBBBCCCCDDDD////. Options: cccc CCCCoooommmmpppplllleeeemmmmeeeennnntttt tttthhhheeee SSSSEEEEAAAARRRRCCCCHHHHLLLLIIIISSSSTTTT.... dddd DDDDeeeelllleeeetttteeee ffffoooouuuunnnndddd bbbbuuuutttt uuuunnnnrrrreeeeppppllllaaaacccceeeedddd cccchhhhaaaarrrraaaacccctttteeeerrrrssss.... ssss SSSSqqqquuuuaaaasssshhhh dddduuuupppplllliiiiccccaaaatttteeee rrrreeeeppppllllaaaacccceeeedddd cccchhhhaaaarrrraaaacccctttteeeerrrrssss.... If the ////cccc modifier is specified, the SEARCHLIST character set is complemented. If the ////dddd modifier is specified, any characters specified by SEARCHLIST not found in REPLACEMENTLIST are deleted. (Note that this is slightly more flexible than the behavior of some ttttrrrr programs, which delete anything they find in the SEARCHLIST, period.) If the ////ssss modifier is specified, sequences of characters that were translated to the same character are squashed down to a single instance of the character. If the ////dddd modifier is used, the REPLACEMENTLIST is always interpreted exactly as specified. Otherwise, if the REPLACEMENTLIST is shorter than the SEARCHLIST, the final character is replicated till it is long enough. If the REPLACEMENTLIST is null, the SEARCHLIST is replicated. This latter is useful for counting characters in a class or for squashing character sequences in a class. Examples: $$$$AAAARRRRGGGGVVVV[[[[1111]]]] ====~~~~ ttttrrrr////AAAA----ZZZZ////aaaa----zzzz////;;;; #### ccccaaaannnnoooonnnniiiiccccaaaalllliiiizzzzeeee ttttoooo lllloooowwwweeeerrrr ccccaaaasssseeee $$$$ccccnnnntttt ==== ttttrrrr////****////****////;;;; #### ccccoooouuuunnnntttt tttthhhheeee ssssttttaaaarrrrssss iiiinnnn $$$$____ 13/Feb/96 perl 5.002 with 18 PERLOP(1) User Contributed Perl Documentation PERLOP(1) $$$$ccccnnnntttt ==== $$$$sssskkkkyyyy ====~~~~ ttttrrrr////****////****////;;;; #### ccccoooouuuunnnntttt tttthhhheeee ssssttttaaaarrrrssss iiiinnnn $$$$sssskkkkyyyy $$$$ccccnnnntttt ==== ttttrrrr////0000----9999////////;;;; #### ccccoooouuuunnnntttt tttthhhheeee ddddiiiiggggiiiittttssss iiiinnnn $$$$____ ttttrrrr////aaaa----zzzzAAAA----ZZZZ////////ssss;;;; #### bbbbooooooookkkkkkkkeeeeeeeeppppeeeerrrr ---->>>> bbbbooookkkkeeeeppppeeeerrrr (((($$$$HHHHOOOOSSSSTTTT ==== $$$$hhhhoooosssstttt)))) ====~~~~ ttttrrrr////aaaa----zzzz////AAAA----ZZZZ////;;;; ttttrrrr////aaaa----zzzzAAAA----ZZZZ//// ////ccccssss;;;; #### cccchhhhaaaannnnggggeeee nnnnoooonnnn----aaaallllpppphhhhaaaassss ttttoooo ssssiiiinnnngggglllleeee ssssppppaaaacccceeee ttttrrrr [[[[\\\\222200000000----\\\\333377777777]]]] [[[[\\\\000000000000----\\\\111177777777]]]];;;; #### ddddeeeelllleeeetttteeee 8888tttthhhh bbbbiiiitttt If multiple translations are given for a character, only the first one is used: ttttrrrr////AAAAAAAAAAAA////XXXXYYYYZZZZ//// will translate any A to X. Note that because the translation table is built at compile time, neither the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote interpolation. That means that if you want to use variables, you must use an _e_v_a_l_(_): eeeevvvvaaaallll """"ttttrrrr////$$$$oooollllddddlllliiiisssstttt////$$$$nnnneeeewwwwlllliiiisssstttt////"""";;;; ddddiiiieeee $$$$@@@@ iiiiffff $$$$@@@@;;;; eeeevvvvaaaallll """"ttttrrrr////$$$$oooollllddddlllliiiisssstttt////$$$$nnnneeeewwwwlllliiiisssstttt////,,,, 1111"""" oooorrrr ddddiiiieeee $$$$@@@@;;;; IIII////OOOO OOOOppppeeeerrrraaaattttoooorrrrssss There are several I/O operators you should know about. A string is enclosed by backticks (grave accents) first undergoes variable substitution just like a double quoted string. It is then interpreted as a command, and the output of that command is the value of the pseudo-literal, like in a shell. In a scalar context, a single string consisting of all the output is returned. In a list context, a list of values is returned, one for each line of output. (You can set $$$$//// to use a different line terminator.) The command is executed each time the pseudo-literal is evaluated. The status value of the command is returned in $$$$???? (see the _p_e_r_l_v_a_r manpage for the interpretation of $$$$????). Unlike in ccccsssshhhh, no translation is done on the return data--newlines remain newlines. Unlike in any of the shells, single quotes do not hide variable names in the command from interpretation. To pass a $ through to the shell you need to hide it with a backslash. The generalized form of backticks is qqqqxxxx////////. (Because backticks always undergo shell expansion as well, see the _p_e_r_l_s_e_c manpage for security concerns.) 13/Feb/96 perl 5.002 with 19 PERLOP(1) User Contributed Perl Documentation PERLOP(1) Evaluating a filehandle in angle brackets yields the next line from that file (newline included, so it's never false until end of file, at which time an undefined value is returned). Ordinarily you must assign that value to a variable, but there is one situation where an automatic assignment happens. _I_f _a_n_d _O_N_L_Y _i_f the input symbol is the only thing inside the conditional of a wwwwhhhhiiiilllleeee loop, the value is automatically assigned to the variable $$$$____. The assigned value is then tested to see if it is defined. (This may seem like an odd thing to you, but you'll use the construct in almost every Perl script you write.) Anyway, the following lines are equivalent to each other: wwwwhhhhiiiilllleeee ((((ddddeeeeffffiiiinnnneeeedddd(((($$$$____ ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>)))))))) {{{{ pppprrrriiiinnnntttt;;;; }}}} wwwwhhhhiiiilllleeee ((((<<<<SSSSTTTTDDDDIIIINNNN>>>>)))) {{{{ pppprrrriiiinnnntttt;;;; }}}} ffffoooorrrr ((((;;;;<<<<SSSSTTTTDDDDIIIINNNN>>>>;;;;)))) {{{{ pppprrrriiiinnnntttt;;;; }}}} pppprrrriiiinnnntttt wwwwhhhhiiiilllleeee ddddeeeeffffiiiinnnneeeedddd(((($$$$____ ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>))));;;; pppprrrriiiinnnntttt wwwwhhhhiiiilllleeee <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; The filehandles STDIN, STDOUT and STDERR are predefined. (The filehandles ssssttttddddiiiinnnn, ssssttttddddoooouuuutttt and ssssttttddddeeeerrrrrrrr will also work except in packages, where they would be interpreted as local identifiers rather than global.) Additional filehandles may be created with the _o_p_e_n_(_) function. See the ooooppppeeeennnn(((()))) entry in the _p_e_r_l_f_u_n_c manpage for details on this. If a <FILEHANDLE> is used in a context that is looking for a list, a list consisting of all the input lines is returned, one line per list element. It's easy to make a _L_A_R_G_E data space this way, so use with care. The null filehandle <> is special and can be used to emulate the behavior of sssseeeedddd and aaaawwwwkkkk. Input from <> comes either from standard input, or from each file listed on the command line. Here's how it works: the first time <> is evaluated, the @@@@AAAARRRRGGGGVVVV array is checked, and if it is null, $$$$AAAARRRRGGGGVVVV[[[[0000]]]] is set to "-", which when opened gives you standard input. The @@@@AAAARRRRGGGGVVVV array is then processed as a list of filenames. The loop wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{ ............ #### ccccooooddddeeee ffffoooorrrr eeeeaaaacccchhhh lllliiiinnnneeee }}}} is equivalent to the following Perl-like pseudo code: uuuunnnnsssshhhhiiiifffftttt((((@@@@AAAARRRRGGGGVVVV,,,, ''''----'''')))) iiiiffff $$$$####AAAARRRRGGGGVVVV <<<< $$$$[[[[;;;; wwwwhhhhiiiilllleeee (((($$$$AAAARRRRGGGGVVVV ==== sssshhhhiiiifffftttt)))) {{{{ ooooppppeeeennnn((((AAAARRRRGGGGVVVV,,,, $$$$AAAARRRRGGGGVVVV))));;;; wwwwhhhhiiiilllleeee ((((<<<<AAAARRRRGGGGVVVV>>>>)))) {{{{ ............ #### ccccooooddddeeee ffffoooorrrr eeeeaaaacccchhhh lllliiiinnnneeee }}}} }}}} 13/Feb/96 perl 5.002 with 20 PERLOP(1) User Contributed Perl Documentation PERLOP(1) except that it isn't so cumbersome to say, and will actually work. It really does shift array @@@@AAAARRRRGGGGVVVV and put the current filename into variable $$$$AAAARRRRGGGGVVVV. It also uses filehandle _A_R_G_V internally--<> is just a synonym for <ARGV>, which is magical. (The pseudo code above doesn't work because it treats <ARGV> as non-magical.) You can modify @@@@AAAARRRRGGGGVVVV before the first <> as long as the array ends up containing the list of filenames you really want. Line numbers ($$$$....) continue as if the input were one big happy file. (But see example under _e_o_f_(_) for how to reset line numbers on each file.) If you want to set @@@@AAAARRRRGGGGVVVV to your own list of files, go right ahead. If you want to pass switches into your script, you can use one of the Getopts modules or put a loop on the front like this: wwwwhhhhiiiilllleeee (((($$$$____ ==== $$$$AAAARRRRGGGGVVVV[[[[0000]]]],,,, ////^^^^----////)))) {{{{ sssshhhhiiiifffftttt;;;; llllaaaasssstttt iiiiffff ////^^^^--------$$$$////;;;; iiiiffff ((((////^^^^----DDDD((((....****))))////)))) {{{{ $$$$ddddeeeebbbbuuuugggg ==== $$$$1111 }}}} iiiiffff ((((////^^^^----vvvv////)))) {{{{ $$$$vvvveeeerrrrbbbboooosssseeee++++++++ }}}} ............ #### ooootttthhhheeeerrrr sssswwwwiiiittttcccchhhheeeessss }}}} wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{ ............ #### ccccooooddddeeee ffffoooorrrr eeeeaaaacccchhhh lllliiiinnnneeee }}}} The <> symbol will return FALSE only once. If you call it again after this it will assume you are processing another @@@@AAAARRRRGGGGVVVV list, and if you haven't set @@@@AAAARRRRGGGGVVVV, will input from STDIN. If the string inside the angle brackets is a reference to a scalar variable (e.g. <$foo>), then that variable contains the name of the filehandle to input from, or a reference to the same. For example: $$$$ffffhhhh ==== \\\\****SSSSTTTTDDDDIIIINNNN;;;; $$$$lllliiiinnnneeee ==== <<<<$$$$ffffhhhh>>>>;;;; If the string inside angle brackets is not a filehandle or a scalar variable containing a filehandle name or reference, then it is interpreted as a filename pattern to be globbed, and either a list of filenames or the next filename in the list is returned, depending on context. One level of $ interpretation is done first, but you can't say <<<<$$$$ffffoooooooo>>>> because that's an indirect filehandle as explained in the previous paragraph. In older version of Perl, programmers would insert curly brackets to force interpretation as a filename glob: <<<<$$$${{{{ffffoooooooo}}}}>>>>. These days, it's consdired cleaner to call the internal function directly as gggglllloooobbbb(((($$$$ffffoooooooo)))), which is probably the right way to 13/Feb/96 perl 5.002 with 21 PERLOP(1) User Contributed Perl Documentation PERLOP(1) have done it in the first place.) Example: wwwwhhhhiiiilllleeee ((((<<<<****....cccc>>>>)))) {{{{ cccchhhhmmmmoooodddd 0000666644444444,,,, $$$$____;;;; }}}} is equivalent to ooooppppeeeennnn((((FFFFOOOOOOOO,,,, """"eeeecccchhhhoooo ****....cccc |||| ttttrrrr ----ssss '''' \\\\tttt\\\\rrrr\\\\ffff'''' ''''\\\\\\\\000011112222\\\\\\\\000011112222\\\\\\\\000011112222\\\\\\\\000011112222''''||||""""))));;;; wwwwhhhhiiiilllleeee ((((<<<<FFFFOOOOOOOO>>>>)))) {{{{ cccchhhhoooopppp;;;; cccchhhhmmmmoooodddd 0000666644444444,,,, $$$$____;;;; }}}} In fact, it's currently implemented that way. (Which means it will not work on filenames with spaces in them unless you have _c_s_h(1) on your machine.) Of course, the shortest way to do the above is: cccchhhhmmmmoooodddd 0000666644444444,,,, <<<<****....cccc>>>>;;;; Because globbing invokes a shell, it's often faster to call _r_e_a_d_d_i_r_(_) yourself and just do your own _g_r_e_p_(_) on the filenames. Furthermore, due to its current implementation of using a shell, the _g_l_o_b_(_) routine may get "Arg list too long" errors (unless you've installed _t_c_s_h(1L) as _/_b_i_n_/_c_s_h). A glob only evaluates its (embedded) argument when it is starting a new list. All values must be read before it will start over. In a list context this isn't important, because you automatically get them all anyway. In a scalar context, however, the operator returns the next value each time it is called, or a FALSE value if you've just run out. Again, FALSE is returned only once. So if you're expecting a single value from a glob, it is much better to say (((($$$$ffffiiiilllleeee)))) ==== <<<<bbbblllluuuurrrrcccchhhh****>>>>;;;; than $$$$ffffiiiilllleeee ==== <<<<bbbblllluuuurrrrcccchhhh****>>>>;;;; because the latter will alternate between returning a filename and returning FALSE. It you're trying to do variable interpolation, it's definitely better to use the _g_l_o_b_(_) function, because the older notation can cause people to become confused with the indirect filehandle notatin. @@@@ffffiiiilllleeeessss ==== gggglllloooobbbb((((""""$$$$ddddiiiirrrr////****....[[[[cccchhhh]]]]""""))));;;; @@@@ffffiiiilllleeeessss ==== gggglllloooobbbb(((($$$$ffffiiiilllleeeessss[[[[$$$$iiii]]]]))));;;; 13/Feb/96 perl 5.002 with 22 PERLOP(1) User Contributed Perl Documentation PERLOP(1) CCCCoooonnnnssssttttaaaannnntttt FFFFoooollllddddiiiinnnngggg Like C, Perl does a certain amount of expression evaluation at compile time, whenever it determines that all of the arguments to an operator are static and have no side effects. In particular, string concatenation happens at compile time between literals that don't do variable substitution. Backslash interpretation also happens at compile time. You can say ''''NNNNoooowwww iiiissss tttthhhheeee ttttiiiimmmmeeee ffffoooorrrr aaaallllllll'''' .... """"\\\\nnnn"""" .... ''''ggggoooooooodddd mmmmeeeennnn ttttoooo ccccoooommmmeeee ttttoooo....'''' and this all reduces to one string internally. Likewise, if you say ffffoooorrrreeeeaaaacccchhhh $$$$ffffiiiilllleeee ((((@@@@ffffiiiilllleeeennnnaaaammmmeeeessss)))) {{{{ iiiiffff ((((----ssss $$$$ffffiiiilllleeee >>>> 5555 ++++ 111100000000 **** 2222********11116666)))) {{{{ ............ }}}} }}}} the compiler will pre-compute the number that expression represents so that the interpreter won't have to. IIIInnnntttteeeeggggeeeerrrr aaaarrrriiiitttthhhhmmmmeeeettttiiiicccc By default Perl assumes that it must do most of its arithmetic in floating point. But by saying uuuusssseeee iiiinnnntttteeeeggggeeeerrrr;;;; you may tell the compiler that it's okay to use integer operations from here to the end of the enclosing BLOCK. An inner BLOCK may countermand this by saying nnnnoooo iiiinnnntttteeeeggggeeeerrrr;;;; which lasts until the end of that BLOCK. 13/Feb/96 perl 5.002 with 23