I am having a difficulty with an arithmetic syntax error.

I am reading the name of text files from the command line and count the number of the lines of each file.

NUM=$(wc -l "$text") 

and then I want to check whether NUM is odd or not.

So I put,

REMAINDER=$(( $NUM % 2 ))
if [ $REMAINDER -ne 0 ] ; then 
    echo "Odd number"

However, it seems like there is a problem with

REMAINDER=$(( $NUM % 2 ))

$NUM doesn't seem to be regarded as a number but a '.txt' file. When I checked NUM by itself and it worked fine...


If you print $NUM, after

NUM=$(wc -l "$text") 

you probably will see (on Linux) a number and a filename on the same line, with some whitespace.

For example:

1842 basic.c

That string isn't a number, and you usually would read just the first token with your choice of shell/sed/awk, etc., to use that as a number.

@steeldriver suggests this for getting just the number:

NUM=$(wc -l < "$text")

which works (tested with Debian).

  • 1
    ... or use wc -l < "$text" (wc should return only the count when reading input via stdin instead of from a named file) – steeldriver Feb 24 '16 at 1:28
  • There are several variations (and aside from Linux, several systems that could be considered). – Thomas Dickey Feb 24 '16 at 1:29
  • Thank you so much for your reply! Yes it prints both the number and the name of the file when I do that. I'll try to take the number only as you suggest! I'll be able to choose your answer in 5 minutes! – pigletwithcurls Feb 24 '16 at 1:31

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