Shell Programming and Scripting

Please help me.
1)I have a file "test.txt" with below content

1546
2346
8765
2380


2)I have a variable called "NUM".
number variable is assigned with 5674
NUM=5674

3) How to subtract the first record with NUM variable?

I tried below but its below awk command but its showing 0 as an result for every record. Please help me how to do this.

Code:

$ cat >test.txt
1546
2346
8765
2380
$ NUM=1287
$ cat test.txt|awk '{print ($NF - $NUM)}'
0
0
0
0

Code:

awk -v v=$NUM '{$1 - v}' test.txt

Alternate solutions similar to your original method...

Code:

cat test.txt | awk 'BEGIN { v=$NUM } {print ($NF - v ) } '

The BEGIN section is executed prior to the main body of code. Here we load the shell variable into a local variable for use in the print statement.

Code:

cat test.txt | awk '{print ($NF - "$NUM" ) } '

The "quotes" protect the variable name from being part of the sub-shell and passes the parent shell information down


The reason why your original code does not work is that awk runs in a sub-shell to the parent with no variables being passed down (don't remember why the BEGIN statement works though... I'll have to research that). Someone please correct me if I'm wrong, but that's sorta the way I remember it (geez I'm getting old... memory is fading!)

There is no reason or advantage of using the command cat in this case. awk can read a file without the need for cat to pipe it to it.