bash snippets

bash_snippets.sh

# read line by line from file
while read p; do
  echo $p
done <file

# change first letter from upper to lower
q="$(tr '[:upper:]' '[:lower:]' <<< ${p:0:1})${p:1}" 

# sed variable substitution
sed "s/$var/r_str/g" file_name >new_file
# take note of the double quote, this is a common pattern in bash, double quote allows sub, single doesn't