topic Re: question on awk and sed in Operating System - HP-UX

question on awk and sed

Charles Li_2 — Thu, 30 Oct 2003 13:14:10 GMT

is it possible to use $variable inside sed and awk:
svar="xyz"
sed -e 's/$tvar/x/'

avar=5
awk '{ print $'$avar' }'

Thanks,Charles

Re: question on awk and sed

Steven E. Protter — Thu, 30 Oct 2003 13:18:28 GMT

For sure yes with sed.

You may need to use the structure ${tvar} first.

Why don't you just try it.

SEP

Re: question on awk and sed

Tom Danzig — Thu, 30 Oct 2003 13:20:39 GMT

In awk the answer is yes.

For example:
BEGIN{
X=50
}
{
printf("%d\n",X)
}

Will print 50.

To pass variables from the shell into awk, use:

awk -v var=value

Re: question on awk and sed

Charles Li_2 — Thu, 30 Oct 2003 13:21:03 GMT

I would have, but I did not know the syntax. Should it be {},[],(),"",'' or ``.

Re: question on awk and sed

Tom Danzig — Thu, 30 Oct 2003 13:23:32 GMT

As Steven says, use curly braces arount the variable name to isolate it. i.e ${varname}

Re: question on awk and sed

Ramkumar Devanathan — Thu, 30 Oct 2003 13:28:12 GMT

Charles,

1. Enclose the regex within double quotes, and not single quotes.
sed -e "s/$tvar/x/" ...

2. Works fine for me.
awk '{ print $'$avar' }'
this works too -
awk "{ print \$$avar ;}" ...

- ramd.

Re: question on awk and sed

Charles Li_2 — Thu, 30 Oct 2003 13:28:20 GMT

Tom,
I want to do the following with awk:

for loop
K=awk '{ print $$loop }'
## giving K a different value each time the loop is executed.
endloop

is this possible?

Re: question on awk and sed

Charles Li_2 — Thu, 30 Oct 2003 13:35:01 GMT

Works great. Thanks to all.

Re: question on awk and sed

Tom Danzig — Thu, 30 Oct 2003 13:35:22 GMT

Charls,

It should be. Remember not to preceed variables in the awk portion with a $. The shell uses the $ but not awk.

Re: question on awk and sed

curt larson_1 — Thu, 30 Oct 2003 13:39:21 GMT

well I guess that depends on what you mean by "inside sed and awk". sed doesn't have support variables. But, it seems what your trying to do is shell expansion of a variable before it is sent to sed.

abc="abc";sed -e 's/$abc/def/'

the shell doesn't do variable substitution with single quotes. So, the above wouldn't do what your wanting. double quotes do, so either of these will do what your wanting to do.

abc="abc";sed -e "s/$abc/def/"
abc="abc";sed -e 's/'$abc'/def/'
once again sed isn't using the variable, the shell is expanding the variable before sed sees it.
abc="abc";sed -e "s/$abc/def/" gets expanded by the shell to
sed -e "s/abc/def/" before the sed command is ever called. So, your making use of a variable in the shell but sed never knows about it.

the same can be done with awk. But awk has methods to used variables and can be passed variables. unless the awk script is very short, i'd use parameter passing with awk because of all the possible misunderstanding that could be caused by which quotes match up and which variables are expanded by the shell and which are used with awk itself.

your awk example could be done as
avar=5
print "1 2 3 4 5" |
awk "{ print \$$avar; }"

Re: question on awk and sed

Hrvoje Dubravica — Fri, 31 Oct 2003 03:25:28 GMT

Best way to use shell variable in awk
is to make it awk variable:

ABC="xyz"

awk -v abc=${ABC} '{print abc}'

In sed just use " instead of '

Kind regards,

Hrvoje