how to cat a text file and save it as a variable

mrobertson · 07-01-2005, 08:57 AM

I have a text file that needs to be read, printed, and then saved as a variable. I know that to read and print a file I would use:

cat filename

But after it is read and printed, how would I save it as a variable. To give everyone a bit more insight on what I am trying to do. I have a text file that is overwritten every second...it looks like this

10
103
45
67

These four values are overwrote by new values every second. I need to find a function to save this as a variable and read the new text file evey second. How would I do this?

bigearsbilly · 07-01-2005, 09:12 AM

Try this....

file:

Code:

use the 'set' command:

Code:

while sleep 1 ; do  
 set -- $( cat 1)
 echo "$1 $2 $3 $4"
 done

10 103 45 67
10 103 45 67
10 103 45 67

etc... etc

jlliagre · 07-01-2005, 09:18 AM

Code:

for i in 0 1 2 3 4 5 6 7 8 9 10
do
  a[$i]="$(<filename)"
  echo "${a[$i]}"
  sleep 1
done

echo "${a[5]}"
echo "${a[10]}"

mrobertson · 07-01-2005, 09:21 AM

Bigearsbilly,

Will this be true if the numbers change? The numbers that I gave in the example will not ever be the same....they are always changing. How would I account for changing numbers?

mrobertson · 07-01-2005, 09:24 AM

jlliarge,

I dont understand the:

for i in 0 1 2 3 4 5 6 7 8 9 10

Could you explain your code better...I am new to shell coding and do not understand what you are tryinging to do. It looks like your setting up an array, but this program will run all day everyday and a new textfile will be generated ever second of the day, therefore; I would not want an array just some type of loop that will constantly read and print out the text file and only stop on a command.

bigearsbilly · 07-01-2005, 09:26 AM

of course.
it cats the file every second.

jlliagre · 07-01-2005, 09:27 AM

Well, you asked for storing the file content in a variable, so I indeed created an array for these variable to be persistants.

if you need not to save the values, you probably neither need a variable:

Code:

while true
do
  cat filename
  sleep 1
done

aluser · 07-01-2005, 09:41 AM

how about:

Code:

foo="`cat filename`"
echo "$foo"

and do the looping part however you like, of course

mrobertson · 07-01-2005, 09:46 AM

jlliagre,

You have me confused now and I am sorry for that. I just dont understand what I need to do. First you told me to use:

Code:

for i in 0 1 2 3 4 5 6 7 8 9 10
do
  a[$i]="$(<filename)"
  echo "${a[$i]}"
  sleep 1
done

echo "${a[5]}"
echo "${a[10]}"

What is the significants of 5 and 10 and why is the array 0-10. You print in the loop and out of the loop. What are you printing each time?
Then you tell me

Code:

while true
do
  cat filename
  sleep 1
done

What will this code do?

mrobertson · 07-01-2005, 09:51 AM

aluser,

If I did something like this:

Code:

while true
do
  foo="`cat filename`"
  echo "$foo"
  sleep 1
done

Would I get the following functionality:

1) Whatever is in filename will be read and set to the variable foo
2) I print foo to the screen
3) Wait and then repeat.........read....set equal to foo.....print......read....set equal to foo.....print..etc

If so what will the done do and how would I ever get out of this loop if I needed to....or is there a better way to structure my loop?

jlliagre · 07-01-2005, 09:52 AM

My sample code is doing what I understood about your requirements.

Precisely storing every second the content of a file in a variable.

Why is the array 0 to 10 ?

why not ? it is just an example.

What is the significants of 5 and 10 ?

Just to show the sixth and eleventh value stored can be retrieved after the loop is ended.

The second code is displaying the content of the file "filename" every second, forever.

This seems to be what you really want, but please clarify your requirements if I'm mistaken.

aluser · 07-01-2005, 09:55 AM

that loop is infinite. You can always hit control-C on your terminal to kill it. If you want some other terminating condition, tell us what it should be : )

The "done" just tells the shell that's where the bottom of the loop is; stuff below done won't be included in the loop. (The shell doesn't know what you mean by indenting the body of the loop; you just do that so it's more readable to a human)

jlliagre · 07-01-2005, 10:09 AM

In the following code, the "foo" variable is totally useless.

Code:

while true
do
  foo="`cat filename`"
  echo "$foo"
  sleep 1
done

This code is strictly equivalent to that one:

Code:

while true
do
  cat filename
  sleep 1
done

or even the smarter:

Code:

while sleep 1
do
  cat filename
done

mrobertson · 07-01-2005, 10:13 AM

jlliarge,

Do you think this is the best way to go for what I am trying to do?

Code:

while sleep 1
do
  cat filename
done

aluser · 07-01-2005, 10:16 AM

well, what are you trying to do? I think that's the problem here : )