I am piping the output of some commands to perl. The output consists of a set of filenames and directories, and I want perl to filter out the ones that are directories. Something like this:
...some commands... | perl -ne 'print $_ unless -d($_);'
The thing is, it is not filtering the directories! For example, output is something like:
test/unit_test/ipc
test/unit_test/ipc/tc1.cpp
test/unit_test/ipc is a directory, but it is still output.
The values of $_ which are read in by the perl one-liner include a trailing newline. Therefore, -d does not even find the directory, let alone recognize that it is a directory.
Here is a solution:
...some commands... | perl -ne 'chomp $_; print "$_\n" unless -d $_ ;'
Note the use of chomp to remove the trailing newline.
In conjunction with -n or -p, -l not only adds a newline to printed strings, it chomps the input. That means your code can be simplified to
...some commands... | perl -nle 'print $_ unless -d $_;'
or even
...some commands... | perl -nle'print if !-d'
Related
I have a text file (input.txt) like this:
NP_414685.4: 15-26, 131-138, 441-465
NP_418580.2: 493-500
NP_418780.2: 36-48, 44-66
NP_418345.2:
NP_418473.3: 1-19, 567-1093
NP_418398.2:
I want a perl one-liner that keeps only those lines in file where ":" is followed by number range (that means, here, the lines containing "NP_418345.2:" and "NP_418398.2:" get deleted). For this I have tried:
perl -ni -e "print unless /: \d/" -pi.bak input.txt del input.txt.bak
But it shows exactly same output as the input file.
What will be the exact pattern that I can match here?
Thanks
First, print unless means print if not -- opposite to what you want.
More to the point, it doesn't make sense using both -n and -p, and when you do -p overrides the other. While both of them open the input file(s) and set up the loop over lines, -p also prints $_ for every iteration. So with it you are reprinting every line. See perlrun.
Finally, you seem to be deleting the .bak file ... ? Then don't make it. Use just -i
Altogether
perl -i -ne 'print if /:\s*\d+\s*-\s*\d+/' input.txt
If you do want to keep the backup file use -i.bak instead of -i
You can see the code equivalent to a one-liner with particular options with B::Deparse (via O module)
Try: perl -MO=Deparse -ne 1 and perl -MO=Deparse -pe 1
This way:
perl -i.bak -ne 'print if /:\s+\d+-\d/' input.txt
This:
perl -ne 'print if /:\s*(\d+\s*-\s*\d+\s*,?\s*)+\s*$/' input.txt
Prints:
NP_414685.4: 15-26, 131-138, 441-465
NP_418580.2: 493-500
NP_418780.2: 36-48, 44-66
NP_418473.3: 1-19, 567-1093
I'm not sure if you want to match lines that are possibly like this:
NP_418580.2: 493-500, asdf
or this:
NP_418580.2: asdf
This answer will not print these lines, if given to it.
I'm looking to delete blank lines in a CSV file, using Perl.
I'm not too sure how to do this, as these lines aren't exactly "blank" (they're just a bunch of commas).
I'd also like to save the output as a file of the same name, overwriting the original.
How could I go about doing this?
edit: I can't use modules or any source code due to network restrictions...
You can do this using a simple Perl one-liner:
perl -i -ne 'print unless /^[,\s]*$/' <filename>
The -n flag assumes this loop around your program:
while(<>) {
print unless /^[,\s]*$/;
}
and the -i flag means inplace and modifies your input file.
Note: If you are worried about losing your data with -i, you can specify -i.bak and perl will automatically write the original file to your <filename>.bak
More of a command line hack,
perl -i -ne 'print if /[^,\r\n]/' file.csv
If you want to put it inside a shell script you can do this ...
#!/bin/sh
$(perl -i -n -e 'print $_ unless ($_ =~ /^\,+$/);' $*)
This question already has answers here:
How can I process options using Perl in -n or -p mode?
(2 answers)
Closed last year.
I often need to run some Perl one-liners for fast data manipulations, like
some_command | perl -lne 'print if /abc/'
Reading from a pipe, I don't need a loop around the command arg filenames. How can I achieve the next?
some_command | perl -lne 'print if /$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 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