How can I grep for a value from a shell variable?

Question

I've been trying to grep an exact shell 'variable' using word boundaries,

grep "\<$variable\>" file.txt

but haven't managed to; I've tried everything else but haven't succeeded.

Actually I'm invoking grep from a Perl script:

$attrval=`/usr/bin/grep "\<$_[0]\>" $upgradetmpdir/fullConfiguration.txt`

$_[0] and $upgradetmpdir/fullConfiguration.txt contains some matching "text".

But $attrval is empty after the operation.

Solution 1

@OP, you should do that 'grepping' in Perl. don't call system commands unnecessarily unless there is no choice.

$mysearch="pattern";
while (<>){
 chomp;
 @s = split /\s+/;
 foreach my $line (@s){
    if ($line eq $mysearch){
      print "found: $line\n";
    }
 }
}

Solution 2

I'm not seeing the problem here:

file.txt:

hello
hi
anotherline

Now,

mala@human ~ $ export GREPVAR="hi"
mala@human ~ $ echo $GREPVAR
hi
mala@human ~ $ grep "\<$GREPVAR\>" file.txt 
hi

What exactly isn't working for you?

Solution 3

Not every grep supports the ex(1) / vi(1) word boundary syntax.

I think I would just do:

grep -w "$variable" ...

Comments

[Jonathan Leffler]

That doesn't expand '$variable' which the user requested. It would also require the exact string, with '<' before and '>' after the text.

[toolic]

I think Guaurav needs to show a small sample of his input file, his desired output, and confirm that $variable should be expanded by the shell. When more details become available, I'll update my answer.

[Charles Stewart]

Quite. In particular, with system commands, you have to worry about which version of the command is installed. Perl is there to make these worries go away.

[aDev]

I think you probably meant to use double quotes there.