I am stuck in a problem in Perl.
I want to read multiple columns in 1 line using while loop.
I know I can achieve this using shell script like below
cat file.txt|while read field1 field2 field3 field4
do
statement1
statement2
done
The same thing I want in Perl but don't understand how to get this.
Please help me.
Thanks in advance,
Sumana
In a loop, you can do this:
#!/usr/bin/perl -w
use strict;
my $file = "MYFILE";
open (my $fh, '<', $file) or die "Can't open $file for read: $!";
my #lines;
while (<$fh>) {
my ($field1, $field2, $field3) = split;
}
close $fh or die "Cannot close $file: $!";
In the loop, Perl will assign $_ the next line of the file, and with no args, split will split that variable on white space.
use
perl -F -ane '....' your file
-F flag will store each field in an array #F.so u can use $F[0] for the first field.
for example:
perl -F -ane 'print $F[0]' your file
will print the first field of every line
if you are concerned about performance:
perl -lne "my($f,$s,$t)=split;print 'first='.$f.' second='.$s.' third='.$t" your_file
for a big example :also check this
Related
I have set of strings say "-f /path/filename1.f", "-f $path/filename2.f", etc in a single file file.f I want to read file.f and extract /path/filename1.f, $path/filename2.f, etc in another file.
I tried finding solution online but it looks like a mess.
Is there any clean and simple solution there for these kind of simple pattern searching?
below is the requirement
Example,
file.f (input file to perl script)
-f /path/filename1.f
-f $path1/filename2.f
-f /path/filename3.f
-f $path2/filename4.f
outputfile.f
/path/filename1.f
$path1/filename2.f
/path/filename3.f
$path2/filename4.f
Basically I just want path string from the file.f
Some perl code to solve your problem:
use strict;
use warnings;
open my $fhi, "<", "file.f" or die "Error: $!";
open my $fho, ">", "output.f" or die "Error: $!";
while( <$fhi> ) { # Read each line in $_ variable
s/^-f //; # Remove "-f " at the beginning of $_
print $fho $_; # print $_ to output.f file
}
close $fhi;
close $fho;
The simplest way is using cut:
cut -f2 -d’ ‘ input_file > output_file
Or you can use Perl:
perl -lane ‘print $F[1]’ input_file > output_file
These solutions extract the second field of the input and print it.
Look into the below solution -
Here everything after -f will be taken out.
#!/usr/bin/perl
use strict;
use warnings;
open(FILE,"<file.f");
while(<FILE>)
print "$1\n" if($_ =~ /^-f\s(.*)/);
}
I have a text file that looks like this:
... //John/box/sandbox/users/abc/project/build/file2
... //John/box/sandbox/users/cde/project/build/file1
... //John/box/sandbox/users/hdf/project/config/file
Using a Perl script, how can I parse this file so that my final output is:
//John/box/sandbox/users/abc/project/
//John/box/sandbox/users/cde/project/
//John/box/sandbox/users/hdf/project/
Basically my ultimate goal is to search for "//" and "project" on the same line and then take everything between them.
Thanks for the fast response, Both doesn't seems to work for me
I'm using perl 5.8.3 build 809
perl -nle 'print $1 if m#(//.*project/)#;' output.txt
use FileHandle;
use Env;
use Tk;
use File::Copy;
open(DAT, "output.txt") || die("Could not open file!");
my $input = <DAT>;
while (<$input>){
chomp;
print "$1\n" if ($_ =~ /(^\/\/.*project\/)/);
}
Everyone thank you for your help. It worked fine, i had to remove ^.
For future questions i will add my work, sorry this is my first question. Human make mistakes :)
my $infile = 'in.txt';
open my $input, '<', $infile or die "Can't open to $infile: $!";
while (<$input>){
chomp;
print "$1\n" if ($_ =~ /(\/\/.*project\/)/);
}
This is simple enough to do as a command-line filter:
perl -nle'print $1 if m#(//.*project/)#;' output.txt
I have a file that looks like this:
I,like
blah...
I want to replace only the first line with 'i,am' to get:
i,am
blah...
These are big files, so this is what I did (based on this):
open(FH, "+< input.txt") or die "FAIL!";
my $header = <FH>;
chop($header);
$header =~ s/I,like/i,am/g;
seek FH, 0, 0; # go back to start of file
printf FH $header;
close FH;
However, I get this when I run it:
i,amke
blah...
I looks like the 'ke' from like is still there. How do I get rid of it?
What I would do is probably something like this:
perl -i -pe 'if ($. == 1) { s/.*/i,am/; }' yourfile.txt
Which will only affect the first line, when the line counter for the current file handle $. is equal to 1. The regex will replace everything except newline. If you need it to match your specific line, you can include that in the if-statement:
perl -i -pe 'if ($. == 1 and /^I,like$/) { s/.*/i,am/; }' yourfile.txt
You can also look into Tie::File, which allows you to treat the file like an array, which means you can simply do $line[0] = "i,am\n". It is mentioned that there may be performance issues with this module, however.
If the replacement has a different length than the original, you cannot use this technique. You can for example create a new file and then rename it to the original name.
open my $IN, '<', 'input.txt' or die $!;
open my $OUT, '>', 'input.new' or die $!;
my $header = <$IN>;
$header =~ s/I,like/i,am/g;
print $OUT $header;
print $OUT $_ while <$IN>; # Just copy the rest.
close $IN;
close $OUT or die $!;
rename 'input.new', 'input.txt' or die $!;
I'd just use Tie::File:
#! /usr/bin/env perl
use common::sense;
use Tie::File;
sub firstline {
tie my #f, 'Tie::File', shift or die $!;
$f[0] = shift;
untie #f;
}
firstline $0, '#! ' . qx(which perl);
Usage:
$ ./example
$ head -2 example
#! /bin/perl
use common::sense;
I have a Long File Say 10000 Lines.
That is same set of Data Repeated , Like 10 lines and next ten line will be Same.
I want to Find Say "ObjectName" String in that file and Count it, How Many Times is appearing in that file.
Can anyone post detailed code. I am new to Perl.
Using Perl:
perl -ne '$x+=s/objname//g;END{print $x,"\n";}' file
Updated:
Since OP wants the solution using handlers:
#!/usr/bin/perl
use warnings;
use strict;
open my $fh , '<' , 'f.txt' or die 'Cannot open file';
my $x=0;
while (<$fh>){
chomp;
$x+=s/objname//g;
}
close $fh;
print "$x";
Here's another option that also addresses your comment about searching in a whole directory:
#!/usr/bin/env perl
use warnings;
use strict;
my $dir = '.';
my $count = 0;
my $find = 'ObjectName';
for my $file (<$dir/*.txt>) {
open my $fh, '<', $file or die $!;
while (<$fh>) {
$count += /\Q$find\E/g;
}
close $fh;
}
print $count;
The glob denoted by <$dir/*.txt> will non-recursively get the names of all text files in the directory $dir. If you want all files, change it to <$dir/*>. Each file is opened and read, line-by-line. The regex /\Q$find\E/g globally matches the contents of $find against each line. The \Q ... \E notation escapes any meta-characters in the string you're looking for, else those characters may interfere with the matching.
Hope this helps!
This could be a one liner in bash
grep "ObjectName " <filename> | wc -l
People keep asking this question and I keep answering it with the same answer from perlfaq5. Now it's something we can point to on Stackoverflow.
From perlfaq5:
The basic idea of inserting, changing, or deleting a line from a text file involves reading and printing the file to the point you want to make the change, making the change, then reading and printing the rest of the file. Perl doesn't provide random access to lines (especially since the record input separator, $/, is mutable), although modules such as Tie::File can fake it.
A Perl program to do these tasks takes the basic form of opening a file, printing its lines, then closing the file:
open my $in, '<', $file or die "Can't read old file: $!";
open my $out, '>', "$file.new" or die "Can't write new file: $!";
while( <$in> )
{
print $out $_;
}
close $out;
Within that basic form, add the parts that you need to insert, change, or delete lines.
To prepend lines to the beginning, print those lines before you enter the loop that prints the existing lines.
open my $in, '<', $file or die "Can't read old file: $!";
open my $out, '>', "$file.new" or die "Can't write new file: $!";
print $out "# Add this line to the top\n"; # <--- HERE'S THE MAGIC
while( <$in> )
{
print $out $_;
}
close $out;
To change existing lines, insert the code to modify the lines inside the while loop. In this case, the code finds all lowercased versions of "perl" and uppercases them. It happens for every line, so be sure that you're supposed to do that on every line!
open my $in, '<', $file or die "Can't read old file: $!";
open my $out, '>', "$file.new" or die "Can't write new file: $!";
print $out "# Add this line to the top\n";
while( <$in> )
{
s/\b(perl)\b/Perl/g;
print $out $_;
}
close $out;
To change only a particular line, the input line number, $., is useful. First read and print the lines up to the one you want to change. Next, read the single line you want to change, change it, and print it. After that, read the rest of the lines and print those:
while( <$in> ) # print the lines before the change
{
print $out $_;
last if $. == 4; # line number before change
}
my $line = <$in>;
$line =~ s/\b(perl)\b/Perl/g;
print $out $line;
while( <$in> ) # print the rest of the lines
{
print $out $_;
}
To skip lines, use the looping controls. The next in this example skips comment lines, and the last stops all processing once it encounters either __END__ or __DATA__.
while( <$in> )
{
next if /^\s+#/; # skip comment lines
last if /^__(END|DATA)__$/; # stop at end of code marker
print $out $_;
}
Do the same sort of thing to delete a particular line by using next to skip the lines you don't want to show up in the output. This example skips every fifth line:
while( <$in> )
{
next unless $. % 5;
print $out $_;
}
If, for some odd reason, you really want to see the whole file at once rather than processing line-by-line, you can slurp it in (as long as you can fit the whole thing in memory!):
open my $in, '<', $file or die "Can't read old file: $!"
open my $out, '>', "$file.new" or die "Can't write new file: $!";
my #lines = do { local $/; <$in> }; # slurp!
# do your magic here
print $out #lines;
Modules such as File::Slurp and Tie::File can help with that too. If you can, however, avoid reading the entire file at once. Perl won't give that memory back to the operating system until the process finishes.
You can also use Perl one-liners to modify a file in-place. The following changes all 'Fred' to 'Barney' in inFile.txt, overwriting the file with the new contents. With the -p switch, Perl wraps a while loop around the code you specify with -e, and -i turns on in-place editing. The current line is in $_. With -p, Perl automatically prints the value of $_ at the end of the loop. See perlrun for more details.
perl -pi -e 's/Fred/Barney/' inFile.txt
To make a backup of inFile.txt, give -i a file extension to add:
perl -pi.bak -e 's/Fred/Barney/' inFile.txt
To change only the fifth line, you can add a test checking $., the input line number, then only perform the operation when the test passes:
perl -pi -e 's/Fred/Barney/ if $. == 5' inFile.txt
To add lines before a certain line, you can add a line (or lines!) before Perl prints $_:
perl -pi -e 'print "Put before third line\n" if $. == 3' inFile.txt
You can even add a line to the beginning of a file, since the current line prints at the end of the loop:
perl -pi -e 'print "Put before first line\n" if $. == 1' inFile.txt
To insert a line after one already in the file, use the -n switch. It's just like -p except that it doesn't print $_ at the end of the loop, so you have to do that yourself. In this case, print $_ first, then print the line that you want to add.
perl -ni -e 'print; print "Put after fifth line\n" if $. == 5' inFile.txt
To delete lines, only print the ones that you want.
perl -ni -e 'print unless /d/' inFile.txt
... or ...
perl -pi -e 'next unless /d/' inFile.txt