Shell Programming and Scripting

imagine it's reading from this file:

Code:

a b c d e f g
h i j k l m n
o p q r s t u
v w x y z 1 2

read splits apart into different variables based on the IFS variable. If you leave IFS alone, it splits text apart on spaces and tabs. It will split properly even given multiple spaces, so your tr -s may be redundant now.

The first loop, it will set A=a, B=b, C=c, D=d, E=e, F=f, G=g.
Second loop, A=h, B=i, C=j, D=k, E=l, F=m, G=n
Third loop, A=o, B=p, C=q, D=r, E=s, F=t, G=u
Fourth loop, A=v, B=w, C=x, D=y, E=z, F=1, G=2
...and then the loop breaks, because read hits the end of file and returns a nonzero value.

At the bottom of the loop, after the do, is where we tell it to read the file, with < df.txt You can redirect files into entire loops, not just single statements, that's one of the really useful things about a shell language.

Will that work if I am trying to compare it to the numbers?
Or would I need to go with

Code:

while read 1 2 3 4 5 6

or will the first one work fine for it?

You already used read. Don't try and confuse yourself, it's not doing anything different than last time.

Read takes variable names. It'll happily put any text in any variable. It doesn't care a thing about numbers. Once you've read into VAR, you use it like $VAR.

But, you can't name a variable a number, but that's a limit of the shell, not a limit of read.

Call the columns something descriptive like DIR or SIZE or what have you so you can understand your own script later.

Then to compare a number

Code:

if [ "${SOMETHING}" -gt "${SOMETHING_ELSE}" ]
then
        ...
fi

Right now this is what comes out for my dfcap.txt:

Used Available FileSystem
20082764 982120 /dev/mapper/live-rw

Assuming I want to compare $capacity to the firs collumn numbers, which are 2082764, what would go into the latter argument in my if statement.

if ($capacity -lt [what would this argument be])

you still miss a space after the ( and before the )

Those small details I am not concerned about. Right now I am just trying to get the proper syntax which will accept my if statement and return a value. I can clean up lack of spaces, etc, when I get it working.

Whatever your first column is. In my example that's A, so "${A}".