eddiecorrigall/bash-101.md

## bash-101.md

      
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    BASH 101

Use a linter for learning bash, here is one highly recommended that is available as a plugin/extension is Sublime-Text and VS Code: Shellcheck
In the meantime, work on some basics through example.
Asking for help... man

# Ask how to use the command `ls`
man ls
In addition, most commands will have an argument -h or --help for a full description.
ls --help
Standard out: Hello world

echo Hello world
# Exclude tailing newline
echo -n Hello world
# Interpret escape chars
echo -e "Hello\nworld"
# Print an environment variable
echo "Hello $USER"
# Display PID
echo $$
# Print return code (retval) of previous command
echo $?
Environment: Variables

# Print environment variables - try this on your own time
# env
# Set environment variable
export TEST=123
echo "My test number is $TEST"

# Unset environment variable
unset TEST
echo "Did we unset the value: TEST='$TEST'?"
Editors

nano and vim
Pagers

less and more
File system

# Print directory
ls

# Print home directory
ls ~

# Print directory and hidden files
ls -a

# Print directories with glob pattern
ls -a ~/.*

# Print all home directory folders starting with D or A using glob pattern
echo ~/{D,A}*
# Change directory to home
cd ~

# Change directory to home
cd /Users/eddie

# Change directory to previous
cd -

# Print expanded home directory
echo ~
# Make a file
touch my-file.txt

# Remove a file
rm my-file.txt
# Make a directory
mkdir my-dir

# Remove a directory
rm -fr my-dir

# Make directory path
mkdir -p my-dir-parent/my-dir-child

# Remove a directory
rm -fr my-dir-parent
# Make a directory
mkdir my-dir

# Move directory to /tmp
mv my-dir /tmp

cp /tmp/my-dir .
# Print the contents of a file
cat /etc/hosts
# Find a file of folder starting from home directory with name .ssh
find ~ -name .ssh
# Print the size of the application directory from top level
du --human-readable --max-depth=1 /Applications/
Homework, learn about: chmod and chown.
Environment


What was the command again? Oh yea, lets use reverse-search!
I didn't quiet find my command... Lets check history.
What environment variables do I have available? I know, Ill check env

cannot show you during demo, might be secrets in there


Networking

# Request a weather update
curl https://wttr.in
# Display file contents of an http file
curl https://www.google.ca/robots.txt
# Get the http status code
curl --request GET --write-out "%{http_code}" --silent --output /dev/null https://www.google.ca/
# Check if a https port is open
nc --zero --verbose google.ca 443
Standard in: Pipes

# Print all lines containing `127.0.0.1` in `/etc/hosts`
grep 127.0.0.1 /etc/hosts
# Print all lines with IPv4 regex pattern
grep -E '\d+\.\d+\.\d+\.\d+' /etc/hosts
# Print all lines containing `localhost` glob pattern
cat /etc/hosts | grep 127.0.0.*
# Append a line to a file owned by root
echo '0.0.0.0 my.dns-override.com' | sudo tee -a /etc/hosts
# Split user part from a url
echo 'edward.corrigall@clearbanc.com' | cut -d@ -f1

# Replace a dot character
echo 'edward.corrigall@clearbanc.com' | cut -d@ -f1 | tr '.' ' '
# Create a file with a multiline string
tee -a hostnames.txt <<EOF
google.com
google.ca
google.ca
yahoo.ca
reddit.com
facebook.com
www.google.com
google.ca
EOF

# Count number of entries
cat hostnames.txt | wc -l

# Sort a file
cat hostnames.txt | sort

# Sort and deduplicate file
cat hostnames.txt | sort -u

# Tally up by unique values, in descending order
cat hostnames.txt | sort | uniq -c | sort -r
# Create a file with a multiline string
tee -a users.csv <<EOF
email,first_name
bob@microsoft.com,Bob
alice@microsoft.com,Alice
EOF

# Display all but the first line of file
cat users.csv | tail -n +2

# Display second column in comma-separated values file
cat users.csv | tail -n +2 | cut -f2 -d,
Capstone Project

Write a bash script to parse a CSV file!
Note: This is for demonstration purposes only. I recommend using CSV Kit.
# Create a little script...

echo 'Parsing a csv file, yay!'

# Print csv header
cat users.csv | head -n 1 | tr ',' ' ' | tr '[a-z]' '[A-Z]'

# Loop through records in a comma-separated values file
for row in $(cat users.csv | tail -n +2); do
    email="$(echo "$row" | cut -f1 -d,)"
    first_name="$(echo "$row" | cut -f2 -d,)"
    echo "Processing record for $first_name"
done