Bash Shell

• The main non-graphical tool to interact with the operating system is Shell.

• In FreeBSD there is no GUI at all.

• Other notable shells: ksh, zsh, dash.

Bash Environment

• Upon the start of the shell, the OS checks for the existence of several files as: ~/.bashrc, ~/.bash_login, ~/.bash_profile, ~/.bash_logout.

• Environment Variables can be viewed by typing env.

• PATH is a relevant environment variable, which has a format of [location]:[location]:...:[location].

• The PATH variable is one of the execution helpers.

Bash Commands and Programs

• Bash has some built-in commands that provide basic functionality.

• Examples are: fg, echo, set, while.

• Most commands that are used in everyday tasks are external mini-programs kept in PATH locations (use which to find the real location).

• man displays help about commands.

Bash Output Redirectors and Special Characters

• ~: current user's home directory.

• *: wildcard that can be used for choosing only certain types of files.

• $(): will be evaluated before the whole statement and will become part of this statement.

• Use command > file.txt format to create a file containing command's output.

• Use command >> file.txt format to append containing command's output to an existing file.

• |: pipe.

• chaining commands is a quite powerful Bash feature, one-liners.

file `ls /etc/*.conf | sort` > test.txt && cat test.txt | wc -l

Bash Conditional Statements and Loops

• chmod +x scriptname so you can execute this script with ./scriptname

echo '#!/bin/bash' > script.sh
echo 'ls /tmp | wc -l' >> script.sh
chmod +x script.sh
./script.sh

if <conditions>; then
<commands>
fi

if [ x ]; then
  docommand
elif [ y ]; then
  doothercommand
else
  dosomethingelse
fi

Conditional statements:

• -eq: equal

• -ne: not equal

• -lt: less than

• -le: less than or equal

• -gt: greater than

• -ge: greater than or equal

Loops:

#!/bin/bash

for i in $(ls); do
  echo item: $i
done

or:

#!/bin/bash
for i in `seq 1 10`;
do
  echo $i
done

While loop:

while [condition]; do command1; command2; done

for example:

while read line; do echo $line; done < file.txt

Filters open ports from nmap output files

cat *.nmap | grep "open" | grep -v "filtered" | cut -d '/' -f 1 | sort -u | xargs | tr ' ' ',' > ports.txt

Fingerprint potential applications:

cat domains.txt
domain1.com
domain2.com

alivecheck.sh:

#!/bin/bash

for protocol in 'http://' 'https://';do
  while read line;
  do
    code=$(curl -L --write-out "%{http_code}\n" --output /dev/null --silent --insecure $protocol$line)
    if [ $code = "000" ]; then
      echo "$protocol$line: not responding."
    else
      echo "$protocol$line: HTTP $code"
      echo "$protocol$line: $code" >> alive.txt
    fi
  done < domains.txt
done