CODEWITHSUNDEEP
linuxbash
Godzilla74
Godzilla74

Reputation: 2502

Check version of program and so something in Bash

I've created a Bash script that runs via a crontab that checks the installed version of nmap on a Linux host. The problem is that for some reason, the check is not working correctly and it's always trying to install nmap again and again...

#!/bin/sh
if ! $(nmap --version | grep -q "7.12"); then
  wget https://nmap.org/dist/nmap-7.12.tar.bz2 -P /tmp/
  cd /tmp && bzip2 -cd nmap-7.12.tar.bz2 | tar xvf -
  cd nmap-7.12
  ./configure --without-zenmap
  make
  make install
  cd ..
  rm nmap-7.12.tar.bz2
  rm -rf nmap-7.12
  reboot
fi

If I check to see if the job is running (which it should once, but never again since the version should match the second time) it is...

 $> ps aux | grep nmap
root     27696 15.4  0.3   2940  1464 ?        R    16:31   0:00 /bin/bash ./configure --disable-option-checking --prefix=/usr/local --without-zenmap --cache-file=/dev/null --srcdir=. --no-create --no-recursion

Running the check from the command line yields (without -q):

 $> nmap --version | grep "7.12"
 Nmap version 7.12 ( https://nmap.org )

What is messed up with my script?

Upvotes: 0

Views: 4287

Answers (1)

that other guy
that other guy

Reputation: 123490

ShellCheck says:

Line 2:
if ! $(nmap --version | grep -q "7.12"); then
     ^-- SC2091: Remove surrounding $() to avoid executing output.

The right way to do this is just:

if ! nmap --version | grep -q "7.12"; then

Your attempt finds the string Nmap version 7.12 ( https://nmap.org ), and because of the $(..) it then tries to run that as a command. This results in an error that you probably should have logged and included in the question:

Nmap: command not found

Since errors are false, the ! makes it true and your code runs every time.

Upvotes: 6

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