Quoting

Quotes modify how the shell interprets text. Three types of quotes for Bash shell

1. Double quotes

prevents most special characters from being interpreted.
Glob characters ( * ? [ ] ) inside quotes are trated literallly.
Allows variable and command substitution.
Example :

echo "The glob characters are *, ? and [ ]"
# Output: The glob characters are *, ? and [ ]

echo "The path is $PATH"
# Output: The path is /usr/bin/custom:/home/sysadmin/bin:...

2. Single quotes

prevents the shell from interpreting any special characters.
Variables, command substitution, and globs are treated literally.

Example :

 echo The car costs $100    # The car costs 00
 echo 'The car costs $100'  # The car costs $100

Escape Character

\ escapes a single character, preventing the shell from interpreting it.
Useful when mixing literal characters and variables in the same string.
Example:

echo "The service costs $1 and the path is $PATH"
#‌⁠⁠The service costs  and the path is /usr/bin/custom:/home/sysadmin/bin:...

echo 'The service costs $1 and the path is $PATH' 
#The service costs $1 and the path is $PATH 

echo The service costs \$1 and the path is $PATH
# Output: The service costs $1 and the path is /usr/bin/custom:/home/sysadmin/bin:...

echo This is the command \`date\`     
# This is the command `date`

3. Back quotes

perform command substitution (execute a command and use its output).

Example:

  date
 # Thu Dec 11 05:55:43 UTC 2025                                                    

  echo Today is date                               
  #Today is date

  echo Today is `date`
  echo Today is $(date)
  # Output: Today is Thu Dec 11 05:55:43 UTC 2025             

  echo This is the command "`date`"               
  # This is the command Thu Dec 11 05:55:43 UTC 2025

Double quotes " – preserve literal text but allow variable and command substitution.

Single quotes ' – preserve text exactly as typed, no substitution.

Back quotes ` – execute the command inside and replace with its output.