I know that normally you can just use touch filename to create new files via command line. But, in the text file I have a list of about 500 cities and states, each on a new line. I need to use command line to create a new text file for each of the cities/states. For example, Texas.txt, New York.txt, California.txt
The name of the file that contains the list is newcities.txt - Is this possible to do in command line or through Perl?
You can do this directly in the shell, no need for perl
cat myfile | while read f; do echo "Creating file $f"; touch "$f"; done
perl -lnwe 'open my $fh,">", "$_.txt" or die "$_: $!";' cities.txt
Using the -l option to autochomp the input. The open will create a new empty file, and the file handle will be autoclosed when it goes out of scope.
how about a simple:
cat fileName | xargs touch
Here's a one-liner in perl, assuming each city is on a new line
perl -ne 'chomp; `touch $_`;' newcities.txt
Here's the script version:
#!/usr/bin/perl
use warnings;
use strict;
open my $fh, "<", "./newcities.txt"
or die "Cannot open file: $!";
while( my $line = <$fh> ){
chomp $line;
system("touch $line");
}
close $fh;
Related
I want to make the same calculations in two similar files, but I do not want to double the code for each file nor to create two scripts for this.
my $file = "file1.txt";
my $tempfile = "file1_temp.txt";
if (not defined $file) {
die "Input file not found";
}
open(my $inputFileHandler, '<:encoding(UTF-8)', $file)
or die "Could not open file '$file' $!";
open(my $outs, '>', $tempfile) or die $!;
/*Calculations made*/
close($outs);
copy($tempfile,$file) or die "Copy failed: $!";
unlink($tempfile) or die "Could not delete the file!\n";
close($inputFileHandler);
So i want to do the exact calculations for file2.txt_temp and copy it in file2.txt is there a way to do it without writing the code again for file2?
Thank you very much.
Write your code as a Unix filter. Read the data from STDIN and write it to STDOUT. Your code will be simpler and your program will be more flexible.
#!/usr/bin/perl
use strict;
use warnings;
while (<STDIN>) {
# do a calculation using the data that is in $_
print $output_data
}
The cleverness is in how you call the program:
$ ./my_clever_filter < file1.txt > file1_out.txt
$ ./my_clever_filter < file2.txt > file2_out.txt
See The Unix Filter Model: What, Why and How? for far more information.
Assuming your code is well written (not manipulating any globals, ...) you could use a for-loop
foreach my $prefix ('file1', 'file2') {
my $file = $prefix . ".txt";
my $tempfile = $prefix . "_temp.txt";
...
}
There is a certain Perl feature that is designed especially for cases like this, and that is this:
$ perl -pi -e'/*Calculations made*/' file1.txt file2.txt ... fileN.txt
Loosely referred to as "in-place edit", which basically does what your code does: It writes to a temp file and then overwrites the original.
Which will apply your calculations to the files named as arguments. If you have complex calculations you can put them in a file and skip the -e'....' part
$ perl -pi foo.pl file1.txt ...
Say for example that your "calculations" consist of incrementing each pair of numbers by 1:
s/(\d+) (\d+)/($1 + 1) . ($2 + 1)/ge
You would do either
$ perl -pi -e's/(\d+) (\d+)/($1 + 1) . ($2 + 1)/ge' file1.txt file2.txt
$ perl -pi foo.pl file1.txt file2.txt
Where foo.pl contains the code.
Be aware that the -i switch is destructive, so make backups before running the command. You can supply a backup extension to save a backup, but that backup is overwritten if you run the command again. E.g. -i.bak.
-p places a while (<>) loop around your code, followed by a print of each line,
-i.bak does the editing of the original file, and saves a backup with the extension, if it is supplied.
I want to search for a string and get the full line from a text file through Perl scripting.
So the text file will be like the following.
data-key-1,col-1.1,col-1.2
data-key-2,col-2.1,col-2.2
data-key-3,col-3.1,col-3.2
Here I want to apply data-key-1 as the search string and get the full line into a Perl variable.
Here I want the exact replacement of grep "data-key-1" data.csv in the shell.
Some syntax like the following worked while running in the console.
perl -wln -e 'print if /\bAPPLE\b/' your_file
But how can I place it in a script? With the perl keyword we can't put it into a script. Is there a way to avoid the loops?
If you'd know the command line options you are giving for your one-liner, you'd know exactly what to write inside your perl script. When you read a file, you need a loop. Choice of loop can yield different results performance wise. Using for loop to read a while is more expensive than using a while loop to read a file.
Your one-liner:
perl -wln -e 'print if /\bAPPLE\b/' your_file
is basically saying:
-w : Use warnings
-l : Chomp the newline character from each line before processing and place it back during printing.
-n : Create an implicit while(<>) { ... } loop to perform an action on each line
-e : Tell perl interpreter to execute the code that follows it.
print if /\bAPPLE\b/ to print entire line if line contains the word APPLE.
So to use the above inside a perl script, you'd do:
#!usr/bin/perl
use strict;
use warnings;
open my $fh, '<', 'your_file' or die "Cannot open file: $!\n";
while(<$fh>) {
my $line = $_ if /\bAPPLE\b/;
# do something with $line
}
chomp is not really required here because you are not doing anything with the line other then checking for an existence of a word.
open($file, "<filename");
while(<$file>) {
print $_ if ($_ =~ /^data-key-3,/);
}
use strict;
use warnings;
# the file name of your .csv file
my $file = 'data.csv';
# open the file for reading
open(FILE, "<$file") or
die("Could not open log file. $!\n");
#process line by line:
while(<FILE>) {
my($line) = $_;
# remove any trail space (the newline)
# not necessary, but again, good habit
chomp($line);
my #result = grep (/data-key-1/, $line);
push (#final, #result);
}
print #final;
I have a lot of text files in a folder. The folder is 'c:\vehicles'. For every text file, I want to copy any row that includes the words: model, make, year. The file I want to write to is 'vehicles.txt' and located in 'c:\'.
I know I've written the code wrong. What should I do to correct it? Thanks for the help.
C:\vehicles $ ls -A | xargs head -qn 30 | perl -Mstrict -wne 'if( $ +_ =~ /(make)|(model)|(year)/ ) { print "$_"; }' > vehicles.txt
grep -rE "(make|model|year)" c:
Perhaps the following will help:
use strict;
use warnings;
for my $file (<*.txt>) {
open my $fh, '<', $file or die $!;
while (<$fh>) {
chomp;
print "$_\n" if /(?:\b(?:model|make|year)\b)/i;
}
close $fh;
}
Assuming the script will be in c:\vehicles, type perl scriptName.pl >vehicles.txt at the command prompt.
The <*.txt> notation returns a list of all text files in the directory. Each of these files are opened and read, line by line. If any of the words your looking for are found on a line, it's printed. The >vehicles.txt notation means to print to the file.
Greetings,
I have the following code and am stuck on how I would proceed to modify it so it will ask for the directory, read all files in the directory, then extract specific strings and ouput to an html file? Thanks in advance.
#!/usr/local/bin/perl
use warnings;
use strict;
use Cwd;
print "Enter filename: "; # Should be Enter directory
my $perlfile =STDIN;
open INPUT_FILE, $perlfile || die "Could not open file: $!";
open OUTPUT, '>out.html' || die "Could not open file: $!";
# Evaluates the file and imports it into an array.
my #comment_array = ;
close(INPUT_FILE);
chomp #comment_array;
#comment_array = grep /^\s*#/g, #comment_array;
my $comment;
foreach $comment (#comment_array) {
$comment =~ /####/; #Pattern match to grab only #s
# Prints comments to screen
Print results in html format
# Writes comments to output.html
Writes results to html file
}
close (OUTPUT);
Take it one step at a time. You have a lot planned, but so far you haven't even changed your prompt string to ask for a directory.
To read the entered directory name, your:
my $perlfile =STDIN;
gives an error (under use strict;). Start by looking that error up (use diagnostics; automates this) and trying to figure out what you should be doing instead.
Once you can prompt for a directory name and print it out, then add code to open the directory and read the directory. Directories can be opened and read with opendir and readdir. Make sure you can read the directory and print out the filenames before going on to the next step.
a good starting point to learn about specific functions (from the cmd line)
perldoc -f opendir
However, your particular problem is answered as follows, you can also use command line programs and pipe them into a string to simplify file handling ('cat') and pattern matching ('grep').
#!/usr/bin/perl -w
use strict;
my $dir = "/tmp";
my $dh;
my #patterns;
my $file;
opendir($dh,$dir);
while ($file = readdir($dh)){
if (-f "$dir/$file"){
my $string = `cat $dir/$file | grep pattern123`;
push #patterns, $string;
}
}
closedir($dh);
my $html = join("<br>",#patterns);
open F, ">out.html";
print F $html;
close F;
file1.txt
hello
tom
well
file2.txt
world
jerry
done
How to merge file1.txt with file2.txt; then create a new file - file3.txt
hello world
tom jerry
well done
thank you for reading and reply.
Attached the completed code which based on the answer.
#!/usr/bin/perl
use strict;
use warnings;
open(F1,"<","1.txt") or die "Cannot open file1:$!\n";
open(F2,"<","2.txt") or die "Cannot open file2:$!\n";
open (MYFILE, '>>3.txt');
while(<F1>){
chomp;
chomp(my $f2=<F2>);
print MYFILE $_ . $f2 ."\n";
}
if Perl is not a must, you can just use paste on *nix. If you are on Windows, you can also use paste. Just download from GNU win32
$ paste file1 file2
else, in Perl
open(F1,"<","file1") or die "Cannot open file1:$!\n";
open(F2,"<","file2") or die "Cannot open file2:$!\n";
while(<F1>){
chomp;
chomp($f2=<F2>);
print $_ . $f2 ."\n";
}
I don't think anyone should give a full answer for this.
Just open both files, then loop through both at the same time and write out to a new file.
If you don't know how to read and write files in perl, here is a tutorial:
http://perl.about.com/od/perltutorials/a/readwritefiles.htm