Perl Learning - 15 (s///)

发布时间：2020-12-15 21:02:16 所属栏目：大数据来源：网络整理

导读：s/// is the most common expression using RE to do "search and replace". ? s/patten/replace/ searches the 'patten' and replaces it to 'replace'. ? 'patten' is the patten we talked in perlRE,it can be a variable though. 'replace' is the char

s/// is the most common expression using RE to do "search and replace".

s/patten/replace/ searches the 'patten' and replaces it to 'replace'.

'patten' is the patten we talked in perlRE,it can be a variable though.
'replace' is the characters whichever you want to replace the result of search,it can be variable too.

$_="He's out bowling with Barney tonight.";
s/Barney/Fred/;?# Barney replaced by Fred
s/with (w+)/agaist $1's team/;
print "$_n";

s/// returns a value: replace success returns true,failure returns false.

$_="fred flintstone";
if(s/fred/wilma/){
?print "Successfully replaced fred with wilma!n";
?print "$_n";
}

/g flag can replace all the result,instead of once by default.

$_="home,sweet home!";
s/home/cave/g;
print "$_n";

$_="?? Input???? data?may have????? extra whitespace.? ";
s/s+/ /g;
print "$_n";

Above example is used to compress multiple whitespaces to one single space.

We can use other symbol in other then s///

$_="?? Input???? data?may have????? extra whitespace.? ";
s<s+>[ ]g;
s(^s+)<>g;
s#s+$##g;
print "$_n";

Note if use the patten symbols different from replace symbols,they need two pairs of () [] {} ... those pair'ed symbols. /// ### !!! ... those single don't have to.

Flags /i /x /s used in m// can also be used in s///

$_="hello 1
hello 2
wilma again
LOL
Fred,WILMA come on!
_ _END_ _
line 1
line 2
line 3";
?s#wilma#Wilma#gi;
?s{_ _END_ _.*}{}gs;
?print;

All wilma/wiLMA/WIlmA are replaced by Wilma,lines starting with '_ _END_ _' all?are deleted.

Also,=~ can be used to replace variables other than $_ by default.

$file_name =~ s#^.*/##s;?# remove all unix style path

/U changes all characters after it to upper case;
/L changes all characters after it to lower case;
/E close the window of /U or /L;
/u changes one character after it to upper case;
/l changes one character after it to loser case;
/u/L changes one character after it to upper case and all other characters to lower case;
/l/U changes one character after it to lower case and all other characters to upper case.

$_ =“I saw Barney with Fred.”;
s/(fred|barney)/U$1/gi;

$_="I saw barney with FREd.";
s/(w+) with (w+)/uL$2E with uL$1/i;
print "$_n";

They can be used in " " as well:

$name="fred flintstone";print "Hello,Lu$nameE,would you LIKE to play a game?n";

（编辑：李大同）

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