Read file for value, loop until value = $foo? - bash

Question

I'm writing a shell script that greps for $foo then counts the number of occurrences then runs a command. Each time that command is run, there is one less instance of $foo in that file. Uncertain on how to continuously read that file and reduce the value in the variable I set.
$count= `grep -o $foo /some/file |wc -w`
until [ $count -eq 0 ]
do
some_command_that_deletes_foo_in_file
done
However I realize that $count is set once at runtime and is not updated. What I want is $count to be updated to the current count in /some/file while the script is looping through /some/file until there is 0 instances of the phrase I'm grepping for. Uncertain to what the best approach is.

Answer 1

Unless you have additional code that you haven't showed us that depends on $count, you don't actually need to count occurrences; you just need to know whether the string appears in the file. For that, you can write:
while grep -q -- "$foo" /some/file ; do
some_command_that_deletes_foo_in_file
done
(using the fact that grep returns success when it finds the value, and failure when it does not, and using the -q flag to suppress its console output).

Answer 2

You could add the grep command inside the loop:
count=$(grep -o "$foo" /some/file |wc -w)
until (( count == 0 ))
do
some_command_that_deletes_foo_in_file
count=$(grep -o "$foo" /some/file |wc -w)
done

Answer 3

You simply want to delete the string "$foo"? Use sed:
sed "/$foo/d" /some/file > /some/other/file
The sed command is an editor. The /$foo/ is taking a regular expression (whatever the value of $foo), finding it in the file. The d tells it to delete the line.
sed doesn't usually do an in place edit. You usually have to write to another file and then to a move. However, some sed commands may have such a parameter. You can check your manage.
Second Try
I think it must take some action or perform some processing or something, and one of its effects is that one of the $foos is gone. (But I could be wrong.) – ruakh yesterday
This is what I get answering these questions at night.
You can take advantage of the fact that grep returns true (i.e. exit value = 0) if it can find your regular expression and false (i.e. exit value not equal to 0) otherwise:
while grep -o -q "$foo" "/some/file"
do
some_command_that_deletes_foo_in_file
done
The -q tells grep not to output anything. Instead, the exit value of grep will be true if the string is found and false if it isn't.
Read your manpage on grep. Some grep commands don't have the -q parameter. In that case, you'l need to redirect both STDOUT and STDERR to /dev/null.
Another tact may be to do your count of the number of lines, and then use that as a counter:
count=$(grep -o "$foo" "/some/file" | wc -w) # $(...) is the preferred syntax over `...`
for loop in {1..$count}
do
some_command_that_deletes_foo_in_file
done
The advantage is that you only grep through the file once (which maybe a long operation). However, your count maybe incorrect if $foo is on more than one line.
A few notes:
The $(...) is preferred over backticks
When you set a variable, you don't use the dollar sign in front of that variable. Note I have count= and not $count=.
Watch spaces. count= $(...) is wrong because there's a space after the equals sign.