Question

I have the following data in a Tab delimited file:

_ DATA _

Col1    Col2     Col3     Col4    Col5
blah1   blah2     blah3   4       someotherText
blahA   blahZ     blahJ   2       someotherText1
blahB   blahT     blahT   7       someotherText2
blahC   blahQ     blahL   10      someotherText3

I want to make sure that the data in 4th column of this file is always an integer. I know how to do this in perl

• Read each line, Store value of 4th column in a variable
• check if that variable is an integer
• if above is true, continue the loop
• else break out of the loop with message saying file data not correct

But how would I do this in a shell script using standard linux/unix filter? My guess would be to use grep, but I am not sure how?

Answer 1

cut -f4 data | LANG=C grep -q '[^0-9]' && echo invalid

• LANG=C for speed
• -q to quit at first error in possible long file

If you need to strip the first line then use tail -n+2 or you could get hacky and use:

cut -f4 data | LANG=C sed -n '1b;/[^0-9]/{s/.*/invalid/p;q}'