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I have ips file with content:

192.168.10.10 3306
192.168.10.20 3306

and my script is:

1 #!/bin/bash
  2
  3 p=0
  4 cat /root/ips | while read host port
  5  do
  6    check_up=$(bash -c 'exec 3<> /dev/tcp/'$host'/'$port';echo $?' 2>/dev/null)
  7     if [ $check_up != 0 ]
  8         then
  9           p=$[$p+1]
 10           echo "(1):p in loop = $p"
 11     fi
 12         echo "(2):p in loop = $p"
 13  done
 14      echo "(3):p out loop = $p"
 15
 16     if [ $p % 2 != 0 ]
 17        then
 18             exit 1
 19      fi
~

and out put is:

[root@db1 ~]# ./new-script.sh
(1):p in loop = 1
(2):p in loop = 1
(1):p in loop = 2
(2):p in loop = 2
(3):p out loop = 0
./new-script.sh: line 16: [: too many arguments

why echo "(3):p out loop = $p" return 0 (first value $p)!? when last value $p is 2 ? also, how to fix the error in line 16?

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3
  • Why do you believe that you're using correct test syntax? Commented Mar 6, 2018 at 15:47
  • @Ignacio Vazquez-Abrams I did not understand you.what do you mean? Commented Mar 6, 2018 at 15:52
  • You're asking two questions - you should only ask one at a time, for the benefit of other people who search for answers before asking themselves. It becomes difficult for searches to find the correct url results when you combine questions. Commented Mar 6, 2018 at 15:58

1 Answer 1

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2

The standard way to do arithmetic in the shell is $((..)). Standard test/[ supports only comparisons and other tests. So, the standard-conforming version would be:

if [ "$(( p % 2 ))" -ne 0 ]; then...

(That only needs the quotes if your IFS contains digits, so usually they're not needed.)

In Bash/ksh/zsh, you could use the (( .. )) construct, which works like a command and allows the test too:

if (( p % 2 != 0 )); then ...

The [[ test seems to allow some arithmetic, but it's a bit picky about the syntax/whitespace, so you probably shouldn't do that.

As for why the assignment to p doesn't persist outside the loop, see

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4
  • Note that [ p%2 -ne 0 ] works in ksh. Commented Mar 6, 2018 at 16:08
  • And in bash. test (and [) absolutely does do integer math if you actually use correct syntax, e. g. if [ $((2+2)) -eq 4 ]; then echo yep; fi. Commented Mar 6, 2018 at 16:14
  • @DopeGhoti, that's not test doing the addition, it's the arithmetic expansion that does it. Commented Mar 6, 2018 at 16:18
  • I should have said, rahter, that [ and test can to integer arithmetic comparison (with the -eq, -ne, -ge, le, -lt, and -gt operators). Commented Mar 6, 2018 at 16:47

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