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How do I evaluate or calculate the return value of a command line? For exemple, I count the number of lines with a grep and I want to know if that value is above X. If so, I want to print the number to a file.

Or I want to substract the value of a grep count to another grep count...

How can I manipulate return values that way ?

Gilles 'SO- stop being evil'
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Philippe Carriere
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1 Answers1

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I think you are mixing two things the return value typically indicates if a command was successful (return value 0) or not (anything else). You can get the return value of a command from the variable $?

grep -c returns the count to stdout, to capture the count you can use something like

variable=$(grep -c pattern filename)

Afterwords you can calculate/access the variable how ever you want. See How to do integer & float calculations, in bash or other languages/frameworks? how to calculate stuff with the output.

Community
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Ulrich Dangel
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  • Yeah that was what I meant. And your answer is perfect ! – Philippe Carriere Jul 04 '12 at 19:54
  • $? is the 8-bit exit status of each program. Values of 0 and 1 have standard definitions. Values 2 through 255 are reserved for the program - it may return more information, check the man page for the particular program. Some usages ignore this extra information, and treat $? value 0 as Success, anything else as Not-Success (Failure). – waltinator Apr 02 '22 at 18:23