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~and s in perl


 
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# 1  
Old 09-11-2013
~and s in perl

HI I am new to perl .

can you lease give me explanation of these commands .


Code:
 
$Program = $0 ; $Program =~ s/.*\/// ;
$MyDir = $0 ; $MyDir =~ s/[^\/]*$// ;
 
what does these lines mean "~ s/.*\/// " ,"~ s/[^\/]*$// " ?
 
use DBI;
use DBD::Oracle qw(:ora_types);
use File::Copy;

what does above lines refer to ?


Code:
 
if ( defined ( $opt_v ) )

what does this mean?

Last edited by zaxxon; 09-11-2013 at 04:09 AM.. Reason: changed icode to code
# 2  
Old 09-11-2013
s/.*\/// - replaces everything in front of / with nothing
s/[^\/]*$// - replaces the characters in between the last / and the end of the string with nothing

Code:
if ( defined ( $opt_v ) ) 

if variable $opt_v is defined
# 3  
Old 09-11-2013
Quote:
Originally Posted by ptappeta
what does these lines mean "~ s/.*\/// " ,"~ s/[^\/]*$// " ?
This is a substitute command similar to sed on the unix shell.
s/.*\/// --> delete all the characters in $Program variable from the beginning till the last occurrence of '/' (rather it substitutes the characters from the beginning till the last occurrence of '/' with nothing)

s/[^\/]*$// --> delete all the characters in $Mydir from the last occurrence of '/' till the end (substitute the characters from the last occurrence of '/' till the end with nothing).

To give a better picture these two 's' commands work similar to "basename" and "dirname" utilities in unix.

Quote:
Code:
use DBI;
use DBD::Oracle qw(:ora_types);
use File::Copy;

what does above lines refer to ?
You're asking the perl compiler to use these modules (load these modules) so that the sub-routines in these modules can be used in your current program. You may want to read more about modules in perl.

Quote:
Code:
 
if ( defined ( $opt_v ) )

what does this mean?
This is plain English: If $opt_v is defined, then do this...

Sometimes $opt_v may not be defined or defined with "undef", in that case, this condition will fail.

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