Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 7 days ago.
Improve this question
I am trying to store grep output in perl into variable using perl, but not working.
my $out = `grep -oP "Name = \K(.*)" $file)`;
ERR:
you have an extraneous parenthesis at the end )
always use strict; use warnings; you should have seen the error: Unrecognized escape \K passed through
input file:
Name = foobar
code:
perl -Mstrict -we 'print qx(grep -oP "Name = \K(.*)" file)'
Unrecognized escape \K passed through at -e line 1.
Finally:
$ perl -Mstrict -we 'my $out = qx(grep -oP "Name = \\K(.*)" file); print $out'
# ^^
foobar
or a more Perlish way to do it:
perl -nE 'say $& if /Name = \K.*/' file
Related
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 2 years ago.
Improve this question
I am using Perl with our printing output system. Usually we call perl scripts, but I am just replacing a keyword with another word. In a console and a test file this worked with this one liner:
perl -pi -e "s/KEYWORD1/KEYWORD2"
Now I wanted to use it with our system and it gives me the error that there is no output file created. As I am fairly new to the field of Perl and want to have it used within a one liner, how can i do this?
Thank you very much for your help.
Kind regards
As Shawn mentioned in the comment, you are missing / in the substitution command s///. You are also missing a filename, which is needed for the -i option.
Both of these fail and print a warning and an error:
perl -pi -e "s/KEYWORD1/KEYWORD2" < foo
# or:
cat foo | perl -pi -e "s/KEYWORD1/KEYWORD2"
They print messages:
-i used with no filenames on the command line, reading from STDIN.
Substitution replacement not terminated at -e line 1.
Correct usage:
perl -pi -e 's/KEYWORD1/KEYWORD2/' foo
# or:
perl -pe 's/KEYWORD1/KEYWORD2/' < foo
# or:
another_command | perl -pe 's/KEYWORD1/KEYWORD2/'
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/, <>;
};
This question already has answers here:
How can I process options using Perl in -n or -p mode?
(2 answers)
Closed last year.
I often need to run some Perl one-liners for fast data manipulations, like
some_command | perl -lne 'print if /abc/'
Reading from a pipe, I don't need a loop around the command arg filenames. How can I achieve the next?
some_command | perl -lne 'print if /$ARGV[0]/' abc
This gives the error:
Can't open abc: No such file or directory.
I understand that the '-n' does the
while(<>) {.... }
around my program, and the <> takes args as filenames, but doing the next every time is a bit impractical
#/bin/sh
while read line
do
some_command | perl -lne 'BEGIN{$val=shift #ARGV} print if /$val/' "$line"
done
Is there some better way to get "inside" the Perl ONE-LINER command line arguments without getting them interpreted as filenames?
Some solutions:
perl -e'while (<STDIN>) { print if /$ARGV[0]/ }' pat
perl -e'$p = shift; while (<>) { print if /$p/ }' pat
perl -e'$p = shift; print grep /$p/, <>' pat
perl -ne'BEGIN { $p = shift } print if /$p/' pat
perl -sne'print if /$p/' -- -p=pat
PAT=pat perl -ne'print if /$ENV{PAT}/'
Of course, it might make more sense to create a pattern that's an ORing or all patterns rather than executing the same command for each pattern.
Also reasonably short:
... | expr=abc perl -lne 'print if /$ENV{expr}/'
Works in bash shell but maybe not other shells.
It depends on what you think will be in the lines you read, but you could play with:
#/bin/sh
while read line
do
some_command | perl -lne "print if /$line/"
done
Clearly, if $line might contain slashes, this is not going to fly. Then, AFAIK, you're stuck with the BEGIN block formulation.
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 $_.scan(/((?:\d{1,3}\.){3}\d{1,3})/)' file
I've been trying to grep an exact shell 'variable' using word boundaries,
grep "\<$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