How do I compare two strings in Perl

Question

How do I compare two strings in Perl   I am learning Perl  I had this basic question looked it up here on StackOverflow and found no good answer so I thought I would ask

User · Answer

And if you d like to extract the differences between the two strings  you can use String  Diff

User · Answer

See perldoc perlop  Use lt  gt  eq  ne  and cmp as appropriate for string comparisons   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  Binary    does a smartmatch between its arguments      lt  le  ge  gt and cmp use the collation  sort  order specified by the current locale if a legacy use locale  but not use locale   not characters   is in effect  See perllocale  Do not mix these with Unicode  only with legacy binary encodings  The standard Unicode  Collate and Unicode  Collate  Locale modules offer much more powerful solutions to collation issues

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print  Matched  n  if   str1 eq  str2    Perl has seperate string comparison and numeric comparison operators to help with the loose typing in the language  You should read perlop for all the different operators

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cmp Compare   a  cmp  b    -1  b  cmp  a     1  a  cmp  a     0  eq Equal to   a  eq   b     0  b  eq   a     0  a  eq   a     1  ne Not-Equal to   a  ne   b     1  b  ne   a     1  a  ne   a     0  lt Less than   a  lt   b     1  b  lt   a     0  a  lt   a     0  le Less than or equal to   a  le   b     1  b  le   a     0  a  le   a     1  gt Greater than   a  gt   b     0  b  gt   a     1  a  gt   a     0  ge Greater than or equal to   a  ge   b     0  b  ge   a     1  a  ge   a     1    See perldoc perlop for more information     I m simplifying this a little bit as all but cmp return a value that is both an empty string  and a numerically zero value instead of 0  and a value that is both the string  1  and the numeric value 1  These are the same values you will always get from boolean operators in Perl  You should really only be using the return values for boolean or numeric operations  in which case the difference doesn t really matter

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In addtion to Sinan   n  r comprehensive listing of string comparison operators  Perl 5 10 adds the smart match operator   The smart match operator compares two items based on their type   See the chart below for the 5 10 behavior  I believe this behavior is changing slightly in 5 10 1    perldoc perlsyn  Smart matching in detail     The behaviour of a smart match depends on what type of thing its arguments are  It is always commutative  i e   a     b behaves the same as  b     a   The behaviour is determined by the following table  the first row that applies  in either order  determines the match behaviour       a       b        Type of Match Implied    Matching Code                                                               overloading trumps everything     Code    Code      referential equality      a     b      Any     Code      scalar sub truth          b-   a        Hash    Hash      hash keys identical       sort keys   a    sort keys   b    Hash    Array     hash slice existence     grep  exists  a-         b   Hash    Regex     hash key grep            grep   b   keys   a   Hash    Any       hash entry existence     exists  a-   b     Array   Array     arrays are identical      Array   Regex     array grep               grep   b     a   Array   Num       array contains number    grep        b    a    Array   Any       array contains string    grep    eq  b    a     Any     undef     undefined                 defined  a   Any     Regex     pattern match             a      b     Code    Code      results are equal         a-    eq  b-      Any     Code      simple closure truth      b-      ignoring  a   Num     numish    numeric equality          a     b      Any     Str       string equality           a eq  b      Any     Num       numeric equality          a     b       Any     Any       string equality           a eq  b       - this must be a code reference whose prototype  if present  is not     subs with a    prototype are dealt with by the  Code    entry lower down     - that is  each element matches the element of same index in the other array  If a circular reference is found  we fall back to referential  equality       - either a real number  or a string that looks like a number   The  matching code  doesn t represent the real matching code  of course  it s just there to explain the intended meaning  Unlike grep  the smart match operator will short-circuit whenever it can   Custom matching via overloading You can change the way that an object is matched by overloading the    operator  This trumps the usual smart match semantics  See overload

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The obvious subtext of this question is      why can t you just use    to check if two strings are the same    Perl doesn t have distinct data types for text vs  numbers   They are both represented by the type  scalar    Put another way  strings are numbers if you use them as such   if   4     4      print  true     else   print  false     true  if    4      4 0      print  true     else   print  false     true  print  3  4 7   Since text and numbers aren t differentiated by the language  we can t simply overload the    operator to do the right thing for both cases   Therefore  Perl provides eq to compare values as text   if    4  eq  4 0      print  true     else   print  false     false  if    4 0  eq  4 0      print  true     else   print  false     true     In short    Perl doesn t have a data-type exclusively for text strings use    or     to compare two operands as numbers use eq or ne  to compare two operands as text   There are many other functions and operators that can be used to compare scalar values  but knowing the distinction between these two forms is an important first step

[perl] How do I compare two strings in Perl?

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