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I currently have 2 bash command line strings I use to gather data needed for a certain task. I was trying to simplify and have only one command used to gather the data without using a script.

First I cat a file and pipe into a grep command and only display the integer value. I then copy and paste that value into an equation which will always be constant except for the grepped value from the first command.

  • 1st command: cat /proc/zem0 |grep -i isrs|grep -Eo '[0-9]+$'
  • 2nd command: echo $(( (2147483633-"**grep value**")/5184000 ))

I'm stumped as to how I can accomplish this. Any guidance on this would be greatly appreciated!

3

Here it is as one command:

echo $(( (2147483633 - $(grep -i isrs /proc/zem0 | grep -Eo '[0-9]+$') )/5184000 ))

How the simplification was done

First consider this pipeline:

cat /proc/zem0 |grep -i isrs`

This can be simplified to:

grep -i isrs /proc/zem0

Thus, the whole of the first command becomes:

grep -i isrs /proc/zem0 | grep -Eo '[0-9]+$'

The last change is to substitute the first command into the second using command substitution: $(...). Thus, we replace:

echo $(( (2147483633-"**grep value**")/5184000 ))

with:

echo $(( (2147483633-$(grep -i isrs /proc/zem0 | grep -Eo '[0-9]+$'))/5184000 ))

One more simplification

If your grep supports perl-style regular expressions, such as GNU grep, then, as suggested by jimmij in the comments, one more simplification is possible:

echo $(( (2147483633-$(grep -Pio 'isrs.*?\K[0-9]+$' /proc/zem0))/5184000 ))
  • Even better to use only one grep with perl regexp: echo $(( (2147483633-"$(grep -Pio 'isrs.*?\K[0-9]+$' /proc/zem0)")/5184000 )) – jimmij Jan 26 '15 at 1:17
  • @jimmij Excellent. I added your idea to the answer. – John1024 Jan 26 '15 at 1:32
  • Thanks for the feedback, folks! This is very useful in helping me understand. – byron Jan 26 '15 at 3:15
  • Hey gents, I tried applying the above solution and am getting a syntax error. Any idea what's happening? -bash: (2147483633-"16463368")/5184000 : syntax error: operand expected (error token is ""16463368")/5184000 ") – byron Jan 26 '15 at 15:55
  • @byron Hmmm. I just revised the answer slightly. Try it now. – John1024 Jan 26 '15 at 17:56
0

Use of command substitution as answered by John1024 is be best way to solve this problem.

Alternatively, you can pipe your output to while read, which will assign each space-separated value to a variable of your choosing. This is usually used when your output has more than one variable you'd like to use.

cat /proc/zem0 |grep -i isrs|grep -Eo '[0-9]+$' | while read myvariable ; do echo $(( (2147483633-"${myvariable}")/5184000 )) ; done

while read is really useful for columnar data, inserting stuff into inventory, etc. E.g. if file1 content is:

host1 192.168.0.100 web nyc1 00-23-54-EE-10-5C
host2 192.168.0.101 web nyc2 00-23-54-EE-10-5D
host3 192.168.0.102 web nyc1 00-23-54-EE-10-5E

then you can do

cat file1 | while read host ip role dc mac ; do
    cobbler system add --name=${host} --ip-address=${ip} --netmask=255.255.255.0 --mac-address=${mac} --comments="${role} ${dc}"
done

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