UNIX for Dummies Questions & Answers

Hi,

I am trying to capture the server load and email me automatically.

This is how it goes

svrload=`uptime|awk '{ print $11 }'`

Now this returns a value say "1.39,".

How do i strip the "," from the returned value and convert this into a whole number to compare with a threshold?

Thanks
Murali

To strip off the last character:

echo "1.39," | perl -pe 's/.$//'

Output: 1.39



If you only want to strip off a comma and ignore anything else, replace the period in that regex with a comma.

ShawnMilo

Awesome, it works. Thanks much.

Can you pls provide a little explanation on this?

Is this the only way to do it (or) is there any other way too?

Would it be possible to round the number too?

Thanks
Murali

You're welcome. There are many ways to do this.

Here's the explanation:

echo "1.39," | perl -pe 's/.$//'

perl -pe
This calls perl. The "p" causes Perl to pass through the input to the output, whether or not it is modified along the way. The "e" indicates to Perl that the expression (code) comes next.

The expression is a simple regex substitution. The period stands for any character, and the dollar sign means "end of line." So this regular expression matches any character at the end of the line. The second part of the regular expression was left empty, so if the first part matches, it's replaced with nothing.

Here's a more verbose regular expression, in Perl syntax, just FYI.

$line =~ s/fred$/barney/;

Here, I substitute "fred" at the end of the line with "barney." In the shorter example, I wanted to eliminate something, so there was nothing between the final two forward-slashes. Also, I didn't use the "variable =~" syntax, because in a Perl one-liner the line of input is assumed by Perl. It can also be explicitly referred to with the $_.

So these two are identical:

echo "1.39," | perl -pe 's/.$//'

echo "1.39," | perl -pe '$_ =~ s/.$//'

Finally, the "=~" syntax sets $_ to the result of running the regular expression substitution on it. In the shorter version that is implicit, and Perl understands it.

ShawnMilo

cool.

Thanks for a detailed explanation.

I always wanted to learn perl language but never got around it.

Thanks

Murali

I prefer Python, but you can't beat Perl one-liners for doing fairly complicated things in a script or on the command line.

Most of what I had to explain above was regular expression syntax, which is a whole different ball of wax. Don't let regexes scare you away from Perl.

I highly recommend Jeffrey Friedl's book "Mastering Regular Expressions." I think the current edition is the third. Read the first 80 or so pages and you'll be a regex champ.

ShawnMilo

$batch = /dataload/R3P/interface/Bowne/reports/RDI00244.rpt

I'd like to strip /dataload/R3P/interface/Bowne/reports/RDI and .rpt from this variable

my output should be only 00244
how to do this using perl regex.I'm a newbie to perl and would like to know how to do this.

thanks and regards,
Ram.