I'm very new to Perl, and I would like to make a program that creates a directory and moves a file into that directory using the Unix command like:
mkdir test
Which I know would make a directory called "test". From there I would like to give more options like:
mv *.jpg test
That would move all .jpg files into my new directory.
So far I have this:
#!/usr/bin/perl
print "Folder Name:";
$fileName = <STDIN>;
chomp($fileType);
$result=`mkdir $fileName`;
print"Your folder was created \n";
Can anyone help me out with this?
Try doing this :
#!/usr/bin/perl
use strict; use warnings;
print "Folder Name:";
$dirName = <STDIN>;
chomp($dirName);
mkdir($dirName) && print "Your folder was created \n";
rename $_, "$dirName/$_" for <*.jpg>;
You will have a better control when using built-in perl functions than using Unix commands. That's the point of my snippet.
Most (if not all) Unix commands have a corresponding version as a function
e.g
mkdir - see here
mv - See here
Etc. either get a print out of the various manual pages (or probably have a trip down to the book shop - O'Reilly nut shell book is quite good along with others).
In perl you can use bash commands in backticks. However, what happens when the directory isn't created by the mkdir command? Your program doesn't get notified of this and continues on its merry way thinking that everything is fine.
You should use built in command in perl that do the same thing.
http://perldoc.perl.org/functions/mkdir.html
http://perldoc.perl.org/functions/rename.html
It is much easier to trap errors with those functions and fail gracefully. In addition, they run faster because you don't have to fork a new process for each command you run.
Perl has some functions similar to those of the shell. You can just use
mkdir $filename;
You can use backquotes to run a shell command, but it is only usefull if the command returns anything to its standard output, which mkdir does not. For commands without output, use system:
0 == system "mv *.jpg $folder" or die "Cannot move: $?";
Related
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($command, #arguments);
For example:
system("sh", "script.sh", "--help" );
system("sh script.sh --help");
System will execute the $command with
#arguments and return to your script when finished. You may check $!
for certain errors passed to the OS by the external application. Read
the documentation for system for the nuances of how various
invocations are slightly different.
2. Using exec
This is very similar to the use of system, but it will
terminate your script upon execution. Again, read the documentation
for exec for more.
3. Using backticks or qx//
my $output = `script.sh --option`;
my $output = qx/script.sh --option/;
The backtick operator and it's equivalent qx//, excute the command and options inside the operator and return that commands output to STDOUT when it finishes.
There are also ways to run external applications through creative use of open, but this is advanced use; read the documentation for more.
From Perl HowTo, the most common ways to execute external commands from Perl are:
my $files = `ls -la` — captures the output of the command in $files
system "touch ~/foo" — if you don't want to capture the command's output
exec "vim ~/foo" — if you don't want to return to the script after executing the command
open(my $file, '|-', "grep foo"); print $file "foo\nbar" — if you want to pipe input into the command
Examples
`ls -l`;
system("ls -l");
exec("ls -l");
Look at the open function in Perl - especially the variants using a '|' (pipe) in the arguments. Done correctly, you'll get a file handle that you can use to read the output of the command. The back tick operators also do this.
You might also want to review whether Perl has access to the C functions that the command itself uses. For example, for ls -a, you could use the opendir function, and then read the file names with the readdir function, and finally close the directory with (surprise) the closedir function. This has a number of benefits - precision probably being more important than speed. Using these functions, you can get the correct data even if the file names contain odd characters like newline.
As you become more experienced with using Perl, you'll find that there are fewer and fewer occasions when you need to run shell commands. For example, one way to get a list of files is to use Perl's built-in glob function. If you want the list in sorted order you could combine it with the built-in sort function. If you want details about each file, you can use the stat function. Here's an example:
#!/usr/bin/perl
use strict;
use warnings;
foreach my $file ( sort glob('/home/grant/*') ) {
my($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks)
= stat($file);
printf("%-40s %8u bytes\n", $file, $size);
}
There are a lot of ways you can call a shell command from a Perl script, such as:
back tick
ls which captures the output and gives back to you.
system
system('ls');
open
Refer #17 here: Perl programming tips
You might want to look into open2 and open3 in case you need bidirectional communication.
I have been using system and qq to run linux programs inside perl. And it has worked well.
#!/usr/bin/perl # A hashbang line in perl
use strict; # It can save you a lot of time and headache
use warnings; # It helps you find typing mistakes
# my keyword in Perl declares the listed variable
my $adduser = '/usr/sbin/adduser';
my $edquota = '/usr/sbin/edquota';
my $chage = '/usr/bin/chage';
my $quota = '/usr/bin/quota';
my $nomeinteiro;
my $username;
my $home;
# system() function executes a system shell command
# qq() can be used in place of double quotes
system qq($adduser --home $home --gecos "$fullname" $username);
system qq($edquota -p john $username);
system qq($chage -E \$(date -d +180days +%Y-%m-%d) $username);
system qq($chage -l $username);
system qq($quota -s $username);
I want to rename *.DIF files to *.SUC files
But the following script is giving "sh: bad substitution" error
I cannot use "rename" becuase my OS is not Linux.
$com="for i in *.DIF; do mv \$i \${i/DIF/SUC}; done;";
print $com."\n";
print `$com`;
Output :
for i in *.DIF; do mv $i ${i/DIF/SUC}; done;
sh: bad substitution
If you are having problems with Perl's rename, use File::Copy, a platform-independent module for moving and copying files. It is a core module, so it should be already part of your Perl installation.
If the system command works when you enter it in the shell, but not in Perl, the most likely reason is that Perl isn't using the shell you expect. We would need more information about your system to be sure, though.
There's no need to shell out for file operations that you can easily do within Perl.
The following renames all of your .dif extension files as .suc.
use strict;
use warnings;
use File::Copy qw(move);
move($_, s/dif$/suc/r) for glob('*.dif');
be default perl was using sh, instead of bash, which allows {//}
this question helped.
Finally I used :
open my $bash_handle, '| bash' or die "Cannot open bash: $!";
print $bash_handle 'for i in *.SUC; do mv $i ${i/SUC/DIF}; done;';
context: I'm a beginner in Perl and struggling, please be patient, thanks.
the question: there is a one-liner that seems to do the job I want (in a cygwin console it does fine on my test file). So now I would need to turn it into a script, but I can't manage that unfortunately.
The one-liner in question is provided in the answer by Aki here Delete lines in perl
perl -ne 'print unless /HELLO/../GOODBYE/' <file_name>
Namely I would like to have a script that opens my file "test.dat" and removes the lines between some strings HELLO and GOODBYE. Here is what I tried and which fails (the path is fine for cygwin):
#!/bin/perl
use strict;
use warnings;
open (THEFILE, "+<test.dat") || die "error opening";
my $line;
while ($line =<THEFILE>){
next if /hello/../goodbye/;
print THEFILE $line;
}
close (THEFILE);
Many thanks in advance!
Your one-liner is equivalent to the following
while (<>) {
print unless /HELLO/../GOODBYE/;
}
Your code does something quite different. You should not attempt to read and write to the same file handle, that usually does not do what you think. When you want to quickly edit a file, you can use the -i "in-place edit" switch:
perl -ni -e 'print unless /HELLO/../GOODBYE/' file
Do note that changes to the file are irreversible, so you should make backups. You can use the backup option for that switch, e.g. -i.bak, but be aware that it is not flawless, as running the same command twice will still overwrite your backup (by saving to the same file name twice).
The simplest and safest way to do it, IMO, is to simply use shell redirection
perl script.pl file.txt > newfile.txt
While using the script file I showed at the top.
What would be an example of how I can call a shell command, say 'ls -a' in a Perl script and the way to retrieve the output of the command as well?
How to run a shell script from a Perl program
1. Using system system($command, #arguments);
For example:
system("sh", "script.sh", "--help" );
system("sh script.sh --help");
System will execute the $command with
#arguments and return to your script when finished. You may check $!
for certain errors passed to the OS by the external application. Read
the documentation for system for the nuances of how various
invocations are slightly different.
2. Using exec
This is very similar to the use of system, but it will
terminate your script upon execution. Again, read the documentation
for exec for more.
3. Using backticks or qx//
my $output = `script.sh --option`;
my $output = qx/script.sh --option/;
The backtick operator and it's equivalent qx//, excute the command and options inside the operator and return that commands output to STDOUT when it finishes.
There are also ways to run external applications through creative use of open, but this is advanced use; read the documentation for more.
From Perl HowTo, the most common ways to execute external commands from Perl are:
my $files = `ls -la` — captures the output of the command in $files
system "touch ~/foo" — if you don't want to capture the command's output
exec "vim ~/foo" — if you don't want to return to the script after executing the command
open(my $file, '|-', "grep foo"); print $file "foo\nbar" — if you want to pipe input into the command
Examples
`ls -l`;
system("ls -l");
exec("ls -l");
Look at the open function in Perl - especially the variants using a '|' (pipe) in the arguments. Done correctly, you'll get a file handle that you can use to read the output of the command. The back tick operators also do this.
You might also want to review whether Perl has access to the C functions that the command itself uses. For example, for ls -a, you could use the opendir function, and then read the file names with the readdir function, and finally close the directory with (surprise) the closedir function. This has a number of benefits - precision probably being more important than speed. Using these functions, you can get the correct data even if the file names contain odd characters like newline.
As you become more experienced with using Perl, you'll find that there are fewer and fewer occasions when you need to run shell commands. For example, one way to get a list of files is to use Perl's built-in glob function. If you want the list in sorted order you could combine it with the built-in sort function. If you want details about each file, you can use the stat function. Here's an example:
#!/usr/bin/perl
use strict;
use warnings;
foreach my $file ( sort glob('/home/grant/*') ) {
my($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks)
= stat($file);
printf("%-40s %8u bytes\n", $file, $size);
}
There are a lot of ways you can call a shell command from a Perl script, such as:
back tick
ls which captures the output and gives back to you.
system
system('ls');
open
Refer #17 here: Perl programming tips
You might want to look into open2 and open3 in case you need bidirectional communication.
I have been using system and qq to run linux programs inside perl. And it has worked well.
#!/usr/bin/perl # A hashbang line in perl
use strict; # It can save you a lot of time and headache
use warnings; # It helps you find typing mistakes
# my keyword in Perl declares the listed variable
my $adduser = '/usr/sbin/adduser';
my $edquota = '/usr/sbin/edquota';
my $chage = '/usr/bin/chage';
my $quota = '/usr/bin/quota';
my $nomeinteiro;
my $username;
my $home;
# system() function executes a system shell command
# qq() can be used in place of double quotes
system qq($adduser --home $home --gecos "$fullname" $username);
system qq($edquota -p john $username);
system qq($chage -E \$(date -d +180days +%Y-%m-%d) $username);
system qq($chage -l $username);
system qq($quota -s $username);
How do I run a Perl script on multiple input files with the same extension?
perl scriptname.pl file.aspx
I'm looking to have it run for all aspx files in the current directory
Thanks!
In your Perl file,
my #files = <*.aspx>;
for $file (#files) {
# do something.
}
The <*.aspx> is called a glob.
you can pass those files to perl with wildcard
in your script
foreach (#ARGV){
print "file: $_\n";
# open your file here...
#..do something
# close your file
}
on command line
$ perl myscript.pl *.aspx
You can use glob explicitly, to use shell parameters without depending to much on the shell behaviour.
for my $file ( map {glob($_)} #ARGV ) {
print $file, "\n";
};
You may need to control the possibility of a filename duplicate with more than one parameter expanded.
For a simple one-liner with -n or -p, you want
perl -i~ -pe 's/foo/bar/' *.aspx
The -i~ says to modify each target file in place, and leave the original as a backup with an ~ suffix added to the file name. (Omit the suffix to not leave a backup. But if you are still learning or experimenting, that's a bad idea; removing the backups when you're done is a much smaller hassle than restoring the originals from a backup if you mess something up.)
If your Perl code is too complex for a one-liner (or just useful enough to be reusable) obviously replace -e '# your code here' with scriptname.pl ... though then maybe refactor scriptname.pl so that it accepts a list of file name arguments, and simply use scriptname.pl *.aspx to run it on all *.aspx files in the current directory.
If you need to recurse a directory structure and find all files with a particular naming pattern, the find utility is useful.
find . -name '*.aspx' -exec perl -pi~ -e 's/foo/bar/' {} +
If your find does not support -exec ... + try with -exec ... \; though it will be slower and launch more processes (one per file you find instead of as few as possible to process all the files).
To only scan some directories, replace . (which names the current directory) with a space-separated list of the directories to examine, or even use find to find the directories themselves (and then perhaps explore -execdir for doing something in each directory that find selects with your complex, intricate, business-critical, maybe secret list of find option predicates).
Maybe also explore find2perl to do this directory recursion natively in Perl.
If you are on Linux machine, you could try something like this.
for i in `ls /tmp/*.aspx`; do perl scriptname.pl $i; done
For example to handle perl scriptname.pl *.aspx *.asp
In linux: The shell expands wildcards, so the perl can simply be
for (#ARGV) {
operation($_); # do something with each file
}
Windows doesn't expand wildcards so expand the wildcards in each argument in perl as follows. The for loop then processes each file in the same way as above
for (map {glob} #ARGV) {
operation($_); # do something with each file
}
For example, this will print the expanded list under Windows
print "$_\n" for(map {glob} #ARGV);
You can also pass the path where you have your aspx files and read them one by one.
#!/usr/bin/perl -w
use strict;
my $path = shift;
my #files = split/\n/, `ls *.aspx`;
foreach my $file (#files) {
do something...
}