awk test if variable is null or empty

fritz001 · 05-30-2013, 06:40 AM

so,

i have on SERVER
/files/backup1
/files/backup2

ssh root@SERVER "ls -l /files/backup1 2>/dev/null|awk '{if(length(\$5)==0){print \"X\"}else{print \$5}}'"

-->i'm getting file size

ssh root@SERVER "ls -l /files/backup2 2>/dev/null|awk '{if(length(\$5)==0){print \"X\"}else{print \%5}}'"

--> i get no result ( was suppose to prin X

Is something I'm missing...

linosaurusroot · 05-30-2013, 08:18 AM

if( (0 + length(\$5)) == 0)

I doubt the backslash is needed. Also there is a % where I think you meant a $. I don't like inbound SSH as root.

fritz001 · 05-30-2013, 08:39 AM

sorry so:

/files/backup2 <-- is missing

in this case
ssh root@SERVER "ls -l /files/backup2 2>/dev/null|awk '{if((0+length(\$5)==0)){print \"X\"}else{print \$5}}'"

"ls -l" should return no value, in this case awk should print "X", but i'm getting nothing...

grail · 05-30-2013, 09:31 AM

You need to think about how awk works ... ie. you pass data to it and it works on the lines of data. Therefore, you pass zero lines to it the awk never starts (kinda), hence no output.

Simple example to test is create an empty file and use:

Code:

awk '{print "hello"}' empty_file

As you will see, 'hello' is never printed as there is no data to work with ... this is the same as what you are doing with no output from ls through the pipe to awk.

fritz001 · 05-30-2013, 09:38 AM

got it, but in this case how do i check the input line fro awk is NULL or has vo value ?

grail · 05-30-2013, 09:45 AM

Maybe you could explain the purpose of what you are doing as this approach seems flawed and parsing ls wouldn't seem to be the way to go?

fritz001 · 05-30-2013, 03:50 PM

i have a perl script:

and i'm trying to make an array of files size , and if file is found to append to array F_size and if not found to put something like 'NULL'.

so the idea is to loop through file and if found the file get the size if not fond... something elese

grail · 05-31-2013, 03:03 AM

hmmm ... colour me still a little confused.

1. Is the perl script run locally or on the servers?

2. I am no perl guru, but am pretty positive it would be able to handle the absence of files and also have functions to retrieve the file size.

pan64 · 05-31-2013, 03:11 AM

you may check the existence of those file in awk, sending filename(s) by stdin over ssh

linosaurusroot · 05-31-2013, 04:09 AM

Quote:

Originally Posted by fritz001

i have a perl script:

and i'm trying to make an array of files size , and if file is found to append to array F_size and if not found to put something like 'NULL'.

so the idea is to loop through file and if found the file get the size if not fond... something elese

Sounds like you want a hash ... test the files with stat() and use the Perl value "undef" when a file is missing.

chrism01 · 05-31-2013, 04:50 AM

Agree with above: do it all in Perl, using a hash and stat() and 'undef'.
http://perldoc.perl.org/