I've been trying to grep an exact shell 'variable' using word boundaries,
grep "\<$variable\>" file.txt
but haven't managed to; I've tried everything else but haven't succeeded.
Actually I'm invoking grep from a Perl script:
$attrval=`/usr/bin/grep "\<$_[0]\>" $upgradetmpdir/fullConfiguration.txt`
$_[0] and $upgradetmpdir/fullConfiguration.txt contains some matching "text".
But $attrval is empty after the operation.
#OP, you should do that 'grepping' in Perl. don't call system commands unnecessarily unless there is no choice.
$mysearch="pattern";
while (<>){
chomp;
#s = split /\s+/;
foreach my $line (#s){
if ($line eq $mysearch){
print "found: $line\n";
}
}
}
I'm not seeing the problem here:
file.txt:
hello
hi
anotherline
Now,
mala#human ~ $ export GREPVAR="hi"
mala#human ~ $ echo $GREPVAR
hi
mala#human ~ $ grep "\<$GREPVAR\>" file.txt
hi
What exactly isn't working for you?
Not every grep supports the ex(1) / vi(1) word boundary syntax.
I think I would just do:
grep -w "$variable" ...
Using single quotes works for me in tcsh:
grep '<$variable>' file.txt
I am assuming your input file contains the literal string: <$variable>
If variable=foo are you trying to grep for "foo"? If so, it works for me. If you're trying to grep for the variable named "$variable", then change the quotes to single quotes.
On a recent linux it works as expected. Do could try egrep instead
Say you have
$ cat file.txt
This line has $variable
DO NOT PRINT ME! $variableNope
$variable also
Then with the following program
#! /usr/bin/perl -l
use warnings;
use strict;
system("grep", "-P", '\$variable\b', "file.txt") == 0
or warn "$0: grep exited " . ($? >> 8);
you'd get output of
This line has $variable
$variable also
It uses the -P switch to GNU grep that matches Perl regular expressions. The feature is still experimental, so proceed with care.
Also note the use of system LIST that bypasses shell quoting, allowing the program to specify arguments with Perl's quoting rules rather than the shell's.
You could use the -w (or --word-regexp) switch, as in
system("grep", "-w", '\$variable', "file.txt") == 0
or warn "$0: grep exited " . ($? >> 8);
to get the same result.
Using single quote it wont work. You should go for double quote
For example:
this wont work
--------------
for i in 1
do
grep '$i' file
done
this will work
--------------
for i in 1
do
grep "$i" file
done
Related
I want the output of the shell command captured in variable of a perl script, only the first section of the command before the pipe "|" is getting executed, and there is no error while executing the script
File.txt
Error input.txt got an error while parsing
Info output.txt has no error while parsing
my $var = `grep Error ./File.txt | awk '{print $2}'`;
print "Errored file $var";
Errored file Error input.txt got an error while parsing
I want just the input.txt which gets filtered by awk command but not happening. Please help
The $ in $2 is interpolated by Perl, so the command that the shell receives looks like:
grep Error ./File.txt | awk '{print }'
(or something else if you have recently matched a regular expression with capture groups). The workaround is to escape the dollar sign:
my $var = `grep Error ./File.txt | awk '{print \$2}'`
Always include use strict; and use warnings; in EVERY perl script.
If you had, you'd have gotten the following warning:
Use of uninitialized value $2 in concatenation (.) or string at scratch.pl line 4.
This would've alerted you to the problem in your command, namely that the $2 variable is being interpolated instead of being treated like a literal.
There are three ways to avoid this.
1) You can do what mob suggested and just escape the $2
my $var = `grep Error ./File.txt | awk '{print \$2}'`
2) You can use the qx form of backticks with single quotes so that it doesn't interpolate, although that is less ideal because you are using single quotes inside your command:
my $var = qx'grep Error ./File.txt | awk \'{print $2}\''
3) You can just use a pure perl solution.
use strict;
use warnings;
my ($var) = do {
local #ARGV = 'File.txt';
map {(split ' ')[1]} grep /Error/, <>;
};
I am trying to do a dynamic search and replace with Perl on the command line with part of the replacement text being the output of a grep command within backticks. Is this possible to do on the command line, or will I need to write a script to do this?
Here is the command that I thought would do the trick. I thought that Perl would treat the backticks as a command substitution, but instead it just treats the backticks and the content within them as a string:
perl -p -i -e 's/example.xml/http:\/\/exampleURL.net\/`grep -ril "example_needle" *`\/example\/path/g' `grep -ril "example_needle" *`
UPDATE:
Thanks for the helpful answers. Yes, there was a typo in my original one-liner: the target file of grep is supposed to be *.
I wrote a small script based on Schewrn's example, but am having confusing results. Here is the script I wrote:
#!/usr/bin/env perl -p -i
my $URL_First = "http://examplesite.net/some/path/";
my $URL_Last = "/example/example.xml";
my #files = `grep -ril $URL_Last .`;
chomp #files;
foreach my $val (#files) {
#dir_names = split('/',$val);
if(#dir_names[1] ne $0) {
my $url = $URL_First . #dir_names[1] . $URL_Last;
open INPUT, "+<$val" or die $!;
seek INPUT,0,0;
while(<INPUT>) {
$_ =~ s{\Q$URL_Last}{$url}g;
print INPUT $_;
}
close INPUT;
}
}
Basically what I am trying to do is:
Find files that contain $URL_Last.
Replace $URL_Last with $URL_First plus the name of the directory that the matched file is in, plus $URL_Last.
Write the above change to the input file without modifying anything else in the input file.
After running my script, it completely garbled the HTML code in the input file and it cut off the first few characters of each line in the file. This is strange, because I know for sure that $URL_Last only occurs once in each file, so it should only be matched once and replaced once. Is this being caused by a misuse of the seek function?
You should use another delimiter for s/// so that you don't need to escape slashes in the URL:
perl -p -i -e '
s#example.xml#http://exampleURL.net/`grep -ril "example_needle"`/example/path#g'
`grep -ril "example_needle" *`
Your grep command inside the regex will not be executed, as it is just a string, and backticks are not meta characters. Text inside a substitution will act as though it was inside a double quoted string. You'd need the /e flag to execute the shell command:
perl -p -i -e '
s#example.xml#
qq(http://exampleURL.net/) . `grep -ril "example_needle"` . qq(/example/path)
#ge'
`grep -ril "example_needle" *`
However, what exactly are you expecting that grep command to do? It lacks a target file. -l will print file names for matching files, and grep without a target file will use stdin, which I suspect will not work.
If it is a typo, and you meant to use the same grep as for your argument list, why not use #ARGV?
perl -p -i -e '
s#example.xml#http://exampleURL.net/#ARGV/example/path#g'
`grep -ril "example_needle" *`
This may or may not do what you expect, depending on whether you expect to have newlines in the string. I am not sure that argument list will be considered a list or a string.
It seems like what you're trying to do is...
Find a file in a tree which contains a given string.
Use that file to build a URL.
Replace something in a string with that URL.
You have three parts, and you could jam them together into one regex, but it's much easier to do it in three steps. You won't hate yourself in a week when you need to add to it.
The first step is to get the filenames.
# grep -r needs a directory to search, even if it's just the current one
my #files = `grep -ril $search .`;
# strip the newlines off the filenames
chomp #files;
Then you need to decide what to do if you get more than one file from grep. I'll leave that choice up to you, I'm just going to take the first one.
my $file = $files[0];
Then build the URL. Easy enough...
# Put it in a variable so it can be configured
my $Site_URL = "http://www.example.com/";
my $url = $Site_URL . $file;
To do anything more complicated, you'd use URI.
Now the search and replace is trivial.
# The \Q means meta-characters like . are ignored. Better than
# remembering to escape them all.
$whatever =~ s{\Qexample.xml}{$url}g;
You want to edit files using -p and -i. Fortunately we can emulate that functionality.
#!/usr/bin/env perl
use strict;
use warnings; # never do without these
my $Site_URL = "http://www.example.com/";
my $Search = "example-search";
my $To_Replace = "example.xml";
# Set $^I to edit files. With no argument, just show the output
# script.pl .bak # saves backup with ".bak" extension
$^I = shift;
my #files = `grep -ril $Search .`;
chomp #files;
my $file = $files[0];
my $url = $Site_URL . $file;
#ARGV = ($files[0]); # set the file up for editing
while (<>) {
s{\Q$To_Replace}{$url}g;
}
Everyone's answers were very helpful to my writing a script that wound up working for me. I actually found a bash script solution yesterday, but wanted to post a Perl answer in case anyone else finds this question through Google.
The script that #TLP posted at http://codepad.org/BFpIwVtz is an alternative way of doing this.
Here is what I ended up writing:
#!/usr/bin/perl
use Tie::File;
my $URL_First = 'http://example.com/foo/bar/';
my $Search = 'path/example.xml';
my $URL_Last = '/path/example.xml';
# This grep returns a list of files containing "path/example.xml"
my #files = `grep -ril $Search .`;
chomp #files;
foreach my $File_To_Edit (#files) {
# The output of $File_To_Edit looks like this: "./some_path/index.html"
# I only need the "some_path" part, so I'm going to split up the output and only use #output[1] ("some_path")
#output = split('/',$File_To_Edit);
# "some_path" is the parent directory of "index.html", so I'll call this "$Parent_Dir"
my $Parent_Dir = #output[1];
# Make sure that we don't edit the contents of this script by checking that $Parent_Dir doesn't equal our script's file name.
if($Parent_Dir ne $0) {
# The $File_To_Edit is "./some_path/index.html"
tie #lines, 'Tie::File', $File_To_Edit or die "Can't read file: $!\n";
foreach(#lines) {
# Finally replace "path/example.xml" with "http://example.com/foo/bar/some_path/path/example.xml" in the $File_To_Edit
s{$Search}{$URL_First$Parent_Dir$URL_Last}g;
}
untie #lines;
}
}
I'm trying to extract all ip addresses from a file. So far, I'm just using
cat foo.txt | perl -pe 's/.*?((\d{1,3}\.){3}\d{1,3}).*/\1/'
but this also prints lines that don't contain a match. I can fix this by piping through grep, but this seems like it ought to be unnecessary, and could lead to errors if the regexes don't match up perfectly.
Is there a simpler way to accomplish this?
Try this:
cat foo.txt | perl -ne 'print if s/.*?((\d{1,3}\.){3}\d{1,3}).*/\1/'
or:
<foo.txt perl -ne 'print if s/.*?((\d{1,3}\.){3}\d{1,3}).*/\1/'
It's the shortest alternative I can think of while still using Perl.
However this way might be more correct:
<foo.txt perl -ne 'if (/((\d{1,3}\.){3}\d{1,3})/) { print $1 . "\n" }'
If you've got grep, then just call grep directly:
grep -Po "(\d{1,3}\.){3}\d{1,3}" foo.txt
You've already got a suitable answer of using grep to extract the IP addresses, but just to explain why you were seeing non-matches being printed:
perldoc perlrun will tell you about all the options you can pass Perl on the command line.
Quoting from it:
-p causes Perl to assume the following loop around your program, which makes it
iterate over filename arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
You could have used the -n switch instead, which does similar, but does not automatically print, for example:
cat foo.txt | perl -ne '/((?:\d{1,3}\.){3}\d{1,3})/ and print $1'
Also, there's no need to use cat; Perl will open and read the filenames you give it, so you could say e.g.:
perl -ne '/((?:\d{1,3}\.){3}\d{1,3})/ and print $1' foo.txt
ruby -0777 -ne 'puts $_.scan(/((?:\d{1,3}\.){3}\d{1,3})/)' file
$ cat test.pl
my $pid = 5892;
my $not = system("top -H -p $pid -n 1 | grep myprocess | wc -l");
print "not = $not\n";
$ perl test.pl
11
not = 0
$
I want to capture the result i.e. 11 into a variable. How can I do that?
From Perlfaq8:
You're confusing the purpose of system() and backticks (``). system() runs a command and returns exit status information (as a 16 bit value: the low 7 bits are the signal the process died from, if any, and the high 8 bits are the actual exit value). Backticks (``) run a command and return what it sent to STDOUT.
$exit_status = system("mail-users");
$output_string = `ls`;
There are many ways to execute external commands from Perl. The most commons with their meanings are:
system() : you want to execute a command and don't want to capture its output
exec: you don't want to return to the
calling perl script
backticks : you want to capture the
output of the command
open: you want to pipe the command (as
input or output) to your script
Also see How can I capture STDERR from an external command?
The easiest way is to use the `` feature in Perl. This will execute what is inside and return what was printed to stdout:
my $pid = 5892;
my $var = `top -H -p $pid -n 1 | grep myprocess | wc -l`;
print "not = $var\n";
This should do it.
Try using qx{command} rather than backticks. To me, it's a bit better because: you can do SQL with it and not worry about escaping quotes and such. Depending on the editor and screen, my old eyes tend to miss the tiny back ticks, and it shouldn't ever have an issue with being overloaded like using angle brackets versus glob.
Using backtick or qx helps, thanks everybody for the answers. However, I found that if you use backtick or qx, the output contains trailing newline and I need to remove that. So I used chomp.
chomp($host = `hostname`);
chomp($domain = `domainname`);
$fqdn = $host.".".$domain;
More information here:
http://irouble.blogspot.in/2011/04/perl-chomp-backticks.html
Use backticks for system commands, which helps to store their results into Perl variables.
my $pid = 5892;
my $not = ``top -H -p $pid -n 1 | grep myprocess | wc -l`;
print "not = $not\n";
Also for eg. you can use IPC::Run:
use IPC::Run qw(run);
my $pid = 5892;
run [qw(top -H -n 1 -p), $pid],
'|', sub { print grep { /myprocess/ } <STDIN> },
'|', [qw(wc -l)],
'>', \my $out;
print $out;
processes are running without bash subprocess
can be piped to perl subs
very similar to shell
I have a file that contains a lot of these
"/watch?v=VhsnHIUMQGM"
and I would like to output the letter code using a perl one-liner. So I try
perl -nle 'm/\"\/watch\?v=(.*?)\"/g' filename.txt
but it doesn't print anything.
What am I doing wrong?
The -n option processes each line but doesn't print anything out. So you need to add an explicit print if you successfully match.
perl -ne 'while ( m/\"\/watch\?v=(.+?)\"/g ) { print "$1\n" }' filename.txt
Another approach, if you're sure every line will match, is to use the -p option which prints out the value of $_ after processing, e.g.:
perl -pe 's/\"\/watch\?v=(.+?)\"/$1//' filename.txt
Your regex is fine. You're getting no output because the -n option won't print anything. It simply wraps a while (<>) { ... } loop around your program (run perl --help for brief explanations of the Perl options).
The following uses your regex, but add some printing. In list context, regexes with the /g option return all captures. Effectively, we print each capture.
perl -nle 'print for m/\"\/watch\?v=(.*?)\"/g' data.dat
You can split the string on "=" instead of matching:
perl -paF= -e '$_= #F[1]' filename.txt