Perl script learning notes

1. When chomp does not have a parameter, use the default parameter to operate on $.
2. array @ array .. can be referenced by $ array [number. $ # Array... indicates the number of indexes in the array.
3. $! Contains error information;
4. By default, the file handle is opened by "<", that is, input. The difference between ">>" and"> "lies in the operation of adding a file handle. Composition Parts.
If (@ argv <2 ){
Die "not enough arguments \ n ";
}
5. Select log; change the default handle; you do not need to enter the handle parameter for subsequent output;
Print log "Hello world! \ N ";
6. opening a new handle will close the previous file handle;
7. My @ k = keys % hash; my @ v = values % hash return key value or variable value;
The exists function in hask determines that a key exists. The delete function deletes the key and value;
8. "." is a metacharacter wildcard. The asterisk ("*") matches the first item zero or multiple times (simple quantifiers). "+" refers to one or more ,"? "Yes indicates not to appear once.
9. "/I" is case-insensitive; "/s" matches any symbol; "/X" adds a space; "/is" is used together ";
10. "m //" actually represents the normal pattern matching "//" you can also use M (), m {}, m <> .. similar to "QW //".
11., \ B, is used for words. For example,/\ bfred \ B/can match the word Fred.
12. $1, $2 is the same as the matching item in the logarithm of brackets in the pattern;
13. The three special variables ($ ', $ &, $') are used to indicate where the match is located, which are left, right, and right.
14. "/s" can be executed only once without "/g;
15. Unless and if are used on the contrary. At the same time, a statement can be formed immediately after the modifier is controlled. elsif is not an elseif statement, but an E is missing;
16. The break and continue of other languages corresponding to last and next. The next loop of redo without a conditional expression directly jumps to the top of the loop content.
17. unlink "file"; rename "old", "new"; Link "file"; mkdir "file", OCT ("permission"); rmdir "file"; chmod 0755, "Fred", "Barney"; chown $ user, $ group, glob "*. O "; utime $ now, $ ago, glob" * ";
18. Index... $ where = index ($ big, $ small); the index returns 0 if it is found at the beginning. If a character is followed, 1 is returned, and so on. If the substring does not exist,-1; rindex... is returned...
19. $ part = substr ($ string, $ initial_position, $ length );
20. My $ money = sprintf "%. 2f", 2.49997;
21. System "date ";
22. My (UNDEF, $ card_num, UNDEF, $ count) = Split /:/;