I have a CGI script that's used by our employees to fetch logs from servers that they don't have direct access to. For reasons I won't go into, after a recent update to our app some of these logs now have characters like linefeeds, tabs, backslashes, etc. translated into their text equivalents. As such, I've modified the CGI script to invoke the following to convert these back to their original values:
perl -i -pe 's/\\r/\r/g && s/\\n/\n/g && s/\\t/\t/g && s/\\\//\//g' $filename
I was just informed that some people are now getting out of memory errors when they try to fetch logs that are fairly large (a few hundred MB).
My question: How does perl manage memory when an inline command like this is invoked? Is it reading the whole file in, processing it, then writing it out, or is it creating a temporary file, processing the lines from the input file one at a time then replacing the file once complete?
This is using perl 5.10.1 on a 64-bit Amazon linux instance.
The -p switch creates a while(<>){...; print} loop to iterate on each “line” in your input file.
If all of your newlines have been converted into "\\n", then your file would just be a single very long line. Therefore, your command would be loading the entire file into memory to perform your fix.
To avoid that, you'll have to intentionally buffer the file using either sysread or $/.
It would probably be easiest to create an actual script instead of a one-liner to do the work. However, if you know that all of your newlines are converted, then one simple fix would be to use $/ = "\\n"
As a secondary note, your regex is flawed. You're currently listing out your translations s/// using a shortcut operator. If any one of the earlier regexes doesn't match for a particular line, then no other translations would be attempted. You should instead use simple semicolons to separate your regexes:
's/\\r/\r/g; s/\\n/\n/g; s/\\t/\t/g; s|\\/|/|g'
Related
I am trying to identify misspelled words with Aspell via Perl. I am working on a Linux server without administrator privileges which means I have access to Perl and Aspell but not, for example, Text::Aspell which is a Perl interface for Aspell.
I want to do the very simple task of passing a list of words to Aspell and having it return the words that are misspelled. If the words I want to check are "dad word lkjlkjlkj" I can do this through the command line with the following commands:
aspell list
dad word lkjlkjlkj
Aspell requires CTRL + D at the end to submit the word list. It would then return "lkjlkjlkj", as this isn't in the dictionary.
In order to do the exact same thing, but submitted via Perl (because I need to do this for thousands of documents) I have tried:
my $list = q(dad word lkjlkjlkj):
my #arguments = ("aspell list", $list, "^D");
my $aspell_out=`#arguments`;
print "Aspell output = $aspell_out\n";
The expected output is "Aspell output = lkjlkjlkj" because this is the output that Aspell gives when you submit these commands via the command line. However, the actual output is just "Aspell output = ". That is, Perl does not capture any output from Aspell. No errors are thrown.
I am not an expert programmer, but I thought this would be a fairly simple task. I've tried various iterations of this code and nothing works. I did some digging and I'm concerned that perhaps because Aspell is interactive, I need to use something like Expect, but I cannot figure out how to use it. Nor am I sure that it is actually the solution to my problem. I also think ^D should be an appropriate replacement for CTRL+D at the end of the commands, but all I know is it doesn't throw an error. I also tried \cd instead. Whatever it is, there is obviously an issue in either submitting the command or capturing the output.
The complication with using aspell out of a program is that it is an interactive and command-line driver tool, as you suspect. However, there is a simple way to do what you need.
In order to use aspell's command list one needs to pass it words via STDIN, as its man page says. While I find the GNU Aspell manual a little difficult to get going with, passing input to a program via its STDIN is easy enough and we can rewrite the invocation as
echo dad word lkj | aspell list
We get lkj printed back, as due. Now this can run out of a program just as it stands
my $word_list = q(word lkj good asdf);
my $cmd = qq(echo $word_list | aspell list);
my #aspell_out = qx($cmd);
print for #aspell_out;
This prints lines lkj and asdf.
I assemble the command in a string (as opposed to an array) for specific reasons, explained below. The qx is the operator form of backticks, which I prefer for its far superior readability.
Note that qx can return all output in a string, if in scalar context (assigned to a scalar for example), or in a list when in list context. Here I assign to an array so you get each word as an element (alas, each also comes with a newline, so may want to do chomp #aspell_out;).
Comment on a list vs string form of a command
I think that it's safe to recommend to use a list-form for a command, in general. So we'd say
my #cmd = ('ls', '-l', $dir); # to be run as an external command
instead of
my $cmd = "ls -l $dir"; # to be run as an external command
The list form generally makes it easier to manage the command, and it avoids the shell altogether.
However, this case is a little different
The qx operator doesn't really behave differently -- the array gets concatenated into a string, and that runs. The very fact that we can pass it an array is incidental, and not even documented
We need to pipe input to aspell's STDIN, and shell does that for us simply. We can use a shell with command's LIST form as well, but then we'd need to invoke it explicitly. We can also go for aspell's STDIN by means other than the shell but that's more complex
With a command in a list the command name must be the first word, so that "aspell list" from the question is wrong and it should fail (there is no command named that) ... except that in this case it wouldn't (if the rest were correct), since for qx the array gets collapsed into a string
Finally, apsell nicely exposes its API in a C library and that's been utilized for the module you mention. I'd suggest to install it as a user (no privileges needed) and use that.
You should take a step back and investigate if you can install Text::Aspell without administrator privilige. In most cases that's perfectly possible.
You can install modules into your home directory. If there is no C-compiler available on the server you can install the module on a compatible machine, compile and copy the files.
I wrote a Perl script to convert from TEX format to JSON format.
Calling in the batch file:
perl -w C:\test\support.pl TestingSample.tex
This is working fine now.
Perl script having two types of input from another program (might be any platform/technology) one is file (*TEX) or else content (*TEX file) either this or that option.
How can I receive the full content as the input to the Perl script?
Now my Perl script is:
my $texfile = $ARGV[0]; my $texcnt = "";
readFileinString($texfile, \$texcnt);
I am trying to update:
perl -w C:/test/support.pl --input $texcnt" #Content is Input
I am receiving error message:
The command line is too long.
Could someone please advice?
First of all regarding the error you're getting:
Perl (or your shell) is complaining that your input argument is too long.
Parsing entire files as arguments to scripts is generally a bad idea anyway, for example quotation mark escaping etc. might not be handled and thus leave a wide open vulnarbility to your entire system!
So the solution to this is to modify your script so that it can take the file as an argument (if that isn't already the case) and if you really need to have an entire file's content parsed as an argument I'd really advise you to create a temporary file in /tmp/ (if on Linux) or in your %TEMP% directory on Windows and parse the file the content into the file and after that give your support.pl script the new temp file as an argument.
I am currently working on a project but I have one big problem. I have some picture with a whitespace in the name and I want to do a montage. The problem is that I can't rename my picture and my code is like that :
$pic1 = qq(picture one.png);
$pic2 = qq(picture two.png);
my $cmd = "C:\...\montage.exe $pic1 $pic2 output.png";
system($cmd);
but because of the whitespace montage.exe doesn't work. How can I execute my code without renaming all my pictures?
Thanks a lot for your answer!
You can properly quote the filenames within the string you pass to system, as #Borodin shows in his answer. Something like: system("montage.exe '$pic1' '$pic2'")
However, A more reliable and safer solution is to pass the arguments to montage.exe as extra parameters in the system call:
system('montage.exe', $pic2, $pic2, 'output.png')
Now you don't have to worry about nesting the correct quotes, or worry about files with unexpected characters. Not only is this simpler code, but it avoids malicious injection issues, should those file names ever come from a tainted source. Someone could enter | rm *, but your system call will not remove all your files for you.
Further, in real life, you probably are not going to have a separate scalar variable for each file name. You'll have them in an array. This makes your system call even easier:
system('montage.exe', #filenames, 'output.png')
Not only is that super easy, but it avoids the pitfall of having a command line too long. If your filenames have nice long paths (maybe 50-100 characters), a Windows command line will exceed the max command length after around 100 files. Passing the arguments through system() instead of in one big string avoids that limitation.
Alternatively, you can pass the arguments to montage.exe as a list (instead of concatenating them all into a string):
use strict;
use warnings;
my $pic1 = qq(picture one.png);
my $pic2 = qq(picture two.png);
my #cmd = ("C:\...\montage.exe", $pic1, $pic2, "output.png");
system(#cmd);
You need to put quotes around the file names that have spaces. You also need to escape the backslashes
my $cmd = qq{C:\\...\\montage.exe "$pic1" "$pic2" output.png};
In unix systems, the best approach is the multi-argument form of system because 1) it avoids invoking a shell, and 2) that's the format accepted by the OS call. Neither of those are true in Windows. The OS call to spawn a program expects a command line, and system's attempt to form this command line is sometimes incorrect. The safest approach is to use Win32::ShellQuote.
use Win32::ShellQuote qw( quote_system );
system quote_system("C:\\...\\montage.exe", $pic1, $pic2, "output.png");
While using tar->write() I am getting errors while using complex file names.
The code is:
my $filename= $archive_type."_".$from_date_time."_".$to_date_time."tar";
$tar->write($filename);
The error i get is:
Could not create filehandle for 'postProcessProbe_2010/6/23/3_2010/6/23/7.tar':
No such file or directory at test.pl line 24
If I change the $filename to a simple string like out.tar everything works.
Well, / is the directory separator on *nix systems (and, internally Windows treats / and \ interchangeably) and I believe tar files, regardless of platform use it internally as the directory separator.
I do not think you can create file names containing / on either *nix or Windows based systems. Even if you could, that would probably create a whole bunch of headaches down the road.
It would be better in my humble opinion to switch to a saner date format such as YYYYMMDD.
Also, you are using string concatenation when sprintf would have been much clearer:
my $filename= sprintf '%s_%s_%s.tar', $archive_type, $from_date_time, , $to_date_time;
I am trying to create my first zsh completion script, in this case for the command netcfg.
Lame as it may sound I have stuck on the first hurdle, disclaimer, I know how to do this crudely, however I seek the "ZSH WAY" to do this.
I need to list the files in /etc/networking but only the files, not the directory component, so I do the following.
echo $(ls /etc/network.d/*(.))
/etc/network.d/ethernet-dhcp /etc/network.d/wireless-wpa-config
What I wanted was:
ethernet-dhcp wireless-wpa-config
So I try (excuse my naivity) :
echo ${(s/*\/)$(ls /etc/network.d/*(.))}
/etc/network.d/ethernet-dhcp /etc/network.d/wireless-wpa-config
It seems that this doesn't work, I'm sure there must be some clever way of doing this by splitting into an array and getting the last part but as I say, I'm complete noob at this.
Any advice gratefully received.
General note: There is no need to use ls to generate the filenames. You might as well use echo some*glob. But if you want to protect the possible embedded newline characters even that is a bad idea. The first example below globs directly into an array to protect embedded newlines. The second one uses printf to generate NUL terminated data to accomplish the same thing without using a variable.
It is easy to do if you are willing to use a variable:
typeset -a entries
entries=(/etc/network.d/*(.)) # generate the list
echo ${entries#/etc/network.d/} # strip the prefix from each one
You can also do it without a variable, but the extra stuff to isolate individual entries is a bit ugly:
# From the inside, to the outside:
# * glob the entries
# * NUL terminate them into a single string
# * split at NUL
# * strip the prefix from each one
echo ${${(0)"$(printf '%s\0' /etc/network.d/*(.))"}#/etc/network.d/}
Or, if you are going to use a subshell anyway (i.e. the command substitution in the previous example), just cd to the directory so it is not part of the glob expansion (plus, you do not have to repeat the directory name):
echo ${(0)"$(cd /etc/network.d && printf '%s\0' *(.))"}
Chris Johnsen's answer is full of useful information about zsh, however it doesn't mention the much simpler solution that works in this particular case:
echo /etc/network.d/*(:t)
This is using the t history modifier as a glob qualifier.
Thanks for your suggestions guys, having done yet more reading of ZSH and coming back to the problem a couple of days later, I think I've got a very terse solution which I would like to share for your benefit.
echo ${$(print /etc/network.d/*(.)):t}
I'm used to seeing basename(1) stripping off directory components; also, you can use echo /etc/network/* to get the file listing without running the external ls program. (Running external programs can slow down completion more than you'd like; I didn't find a zsh-builtin for basename, but that doesn't mean that there isn't one.)
Here's something I hope will help:
haig% for f in /etc/network/* ; do basename $f ; done
if-down.d
if-post-down.d
if-pre-up.d
if-up.d
interfaces