topic Re: grep function in perl in Operating System - HP-UX

grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 10:20:20 GMT

How to incorporate "grep -w $variable" in perl grep? eg:
@ps = grep(/$variable*/, @ps);
Thanks

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 10:30:36 GMT

Use the \b anchor which denote word boundaries in Perl regexps.
Place your match (i.e. $variable) within these.
See also "perldoc perlre"

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 10:30:48 GMT

@ps = grep /\b$variable\b/ => @ps;

Enjoy, Have FUN! H.Merijn [ a more detailed question could have caused a more verbose answer ]

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 10:55:19 GMT

An image says more than thousand words it says.
So procura has given you the image of my clumsy description.
However, don't let yourself get confused by his style.
The => is, as they say, syntactic sugar the professinals use to discern themselves from us mortal Perl foot folk.
grep really takes a list as argument.
see "perldoc -f grep"

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 10:59:00 GMT

Ah something else I realized.
You are reading and assigning to the array @ps at the same time.
Beware the this will only substitute the leading array elements that produced a match.
The tail holds still the old array elements.
So this may not exactly be what you expect,
especially if you rely on the array's dimension (e.g. in scalar context)

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 10:59:21 GMT

Ah something else I realized.
You are reading and assigning to the array @ps at the same time.
Beware that this will only substitute the leading array elements that produced a match.
The tail holds still the old array elements.
So this may not exactly be what you expect,
especially if you rely on the array's dimension (e.g. in scalar context)

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 11:23:47 GMT

Thanks for replies.
where to find detailed documentation of \b$variable\b.

perldoc -f grep is very short.

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 11:56:43 GMT

I told you already, read "perldoc perlre"

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 12:28:28 GMT

Ralph, no!

@ps = .... @ps

grep / map / function / whatever

*REPLACES*

@ps completely. No tail or head will remain.

BTW If @ps refers to a process list (e.g. from `ps`), I'd suggest having a look at Proc::ProcessTable

Enjoy, Have FUN! H.Merijn

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 12:34:49 GMT

Sorry for spreading lies.

I just verified in the debugger,
procura's right.

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 12:38:35 GMT

No debugger needed. An image again :)

lt09:/home/merijn 104 > perl -le'$,=" ";@a=(1..20);print@a;@a=grep/7/,@a;print@a'
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
7 17
lt09:/home/merijn 105 >

Enjoy, Have FUN! H.Merijn

Re: grep function in perl

Ralph Grothe — Mon, 27 Jun 2005 12:49:15 GMT

For geeks like you that's ok.
But for me it would take longer to fumble up the oneliner than running "perl -de0", and doing two line assignments.
Who cares, our boxes have plenty of RAM.

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 12:58:48 GMT

variable=/ABC/SVR; ps -ef | grep $variable
returns
/ABC/SVR1
/ABC/SVR
/ABC/SVR3
/ABC/SVR4
etc

variable=/ABC/SVR; ps -ef | grep -w $variable
returns nothing, but I wanted /ABC/SVR

I also want to get /ABC/SVR from:

variable=/ABC/SVR; perl -e 'print grep(/\b$variable\b/, `ps -ef`)'
does not return anything and I wanted /ABC/SVR

Please advise.

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 13:23:52 GMT

However,
perl -e 'print grep(/\bSVR\b/, `ps -ef`)'
does print only /ABC/SVR

but

perl -e 'print grep(/\b\/ABC\/SVR\b/, `ps -ef`)'
returns nothing. I'm confused and what am I doing wrong.

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 13:31:22 GMT

Hah! HAH!

You were not specific enough in the first quest. You were refering to an EXTERNAL or ENVIRONMENT (shell) variable, not to a perl variable

variable=/ABC/SVR; perl -e 'print grep(/\b$ENV{variable}\b/, `ps -ef`)'

Enjoy, Have FUN! H.Merijn

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 13:40:34 GMT

HI:
variable=/ABC/SVR; perl -e 'print grep(/\b$ENV{variable}\b/,`ps -ef`)'
is returning all the systems processes :(
Any ideas? Thanks

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 13:48:55 GMT

yes I have, but I do not know if that is applicable in your shell

$ variable=blah;echo $variable; perl -le'print$ENV{variable}'
blah

$ export variable=blah;echo $variable; perl -le'print$ENV{variable}'
blah
blah
$ env variable=blah perl -le'print$ENV{variable}'
blah
$

you are setting a 'shell' variable, not an environment variable. Variables set the way you do, are not available to other processes than the shell itself
You will need either export or env

Now you grep using a $ENV that's empty, so you grep on /\b\b/, which is probably not what you tought to do.

I'm using a tcsh, which would need setenv instead of export. 'env' works in all shells

Enjoy, Have FUN! H.Merijn [ think about your points please ]

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 14:36:13 GMT

export variable=/NSG/SVR; perl -le 'print grep(/$ENV{variable}/,`ps -ef`)'
returns:
/NSG/SVR3
/NSG/SVR
/NSG/SVR2
/NSG/SVR1
etc

but:
export variable=/NSG/SVR; perl -le 'print grep(/\b$ENV{variable}\b/,`ps -ef`)'
returns nothing

More points issued if able to find a solution. Thanks

Re: grep function in perl

Mike_Ca Li — Mon, 27 Jun 2005 14:44:56 GMT

variable=/ABC/SVR; perl -le 'print grep(/$ENV{variable}\b/,`ps -ef`)'
returns /ABC/SVR

Thanks all for replies

Re: grep function in perl

H.Merijn Brand (procura — Mon, 27 Jun 2005 14:48:28 GMT

What if you drop the first \b?
I'm still baffled though. This should work!

Totally besides the point: the paren's are not needed with grep.

# export variable=/NSG/SVR; perl -le 'print grep(/\b$ENV{variable}\b/,`ps -ef`)'

Just to easy my curiousity: what does env do?

# env variable=/NSG/SVR perl -le 'print grep /\b$ENV{variable}\b/, `ps -ef`'

And what perl version do you use

# perl -v

Enjoy, Have FUN! H.Merijn [ please point *all* answers. 0 is better than unassigned ]