filehandle regex

pinnacle has asked for the wisdom of the Perl Monks concerning the following question:

Question

I am trying to print line above the the regex in below program in if statement in the file. I am using $` but it does not display any output. I checked my syntax which is correct. Please assist

#!/usr/bin/perl

use strict;

open(ORA, "/usr/cle_un");

while(<ORA>){

print "test: $`\n" if /^Func_file_permission$/;

}
close(ORA);
[download]

File details

ram: 702
Func: Func_file_permission
testing

tam: 768
Func: Func_file_permission
test

cham: 803
Func: Func_file_permission
test
[download]

I want my results to show:

ram: 702
tam: 768
cham:803
[download]

Comment on filehandle regex Select or Download Code

Replies are listed 'Best First'.
Re: filehandle regex by ikegami (Patriarch) on Nov 16, 2010 at 19:57 UTC
I am using $` but it does not display any output. There's nothing before /^/ in the matched variable, so there's nothing in $`. The solution is to stop overwriting the value you want. `my $prev; while (<>) { print($prev) if /^Func_file_permission$/; $prev = $_; }` [download]	[reply] [d/l] [select]
Re: filehandle regex by jwkrahn (Abbot) on Nov 16, 2010 at 20:43 UTC
`$ echo " ram: 702 Func: Func_file_permission testing tam: 768 Func: Func_file_permission test cham: 803 Func: Func_file_permission test " \| perl -e' local $/ = ""; while ( <> ) { print /\A(.*\n)/ if /Func_file_permission$/m; } ' ram: 702 tam: 768 cham: 803` [download]	[reply] [d/l]
Re: filehandle regex by 7stud (Deacon) on Nov 16, 2010 at 20:13 UTC
Also learn to open() a file correctly: `open my $INFILE, '<', 'filename' or die "Couldn't open file: $!"; while (my $line = <$INFILE>) { ...` [download]	[reply] [d/l]
Re: filehandle regex by JavaFan (Canon) on Nov 16, 2010 at 20:59 UTC
To print the previous line, one way of doing it is: `my $prev = ""; while (<ORA>) { print $prev if /^Func_file_permission$/; $prev = $_; }` [download]	[reply] [d/l]
Re^2: filehandle regex by pinnacle (Acolyte) on Nov 17, 2010 at 00:21 UTC
Thanks for the solution it works!! One thing I don't understand why we are using my $prev = ""; also $prev = $_; due to which I am getting previous line from the file What's the magic behind it Thanks!!	[reply]
Re^3: filehandle regex by CountZero (Bishop) on Nov 17, 2010 at 06:58 UTC
Yes, it will also work, but then the script will not run under `use strict;`. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply] [d/l]
Re^3: filehandle regex by JavaFan (Canon) on Nov 17, 2010 at 09:54 UTC
The `my $prev` part is there to properly declare the variable. The `= ""` is there to not have warnings if the first line actually matches. The `;` is there to separate statements.	[reply] [d/l] [select]
Re: filehandle regex by CountZero (Bishop) on Nov 17, 2010 at 07:18 UTC
If you are sure the data you want is always on the first line of each block, you could try this: `use Modern::Perl; { local $/ = ''; say +(split /\n/)[0] while <DATA>; } __DATA__ ram: 702 Func: Func_file_permission testing tam: 768 Func: Func_file_permission test cham: 803 Func: Func_file_permission test` [download] CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply] [d/l]
Re: filehandle regex by aquarium (Curate) on Nov 16, 2010 at 22:38 UTC
instead of using the following static text line as an anchor..why not use a regex to match what looks like a pattern...e.g. `/^[a-z]+:\s[0-9]+$/` the hardest line to type correctly is: stty erase ^H	[reply] [d/l]