5 Common Bash Variable Mistakes and How to Avoid Them

Linux Bash scripting supports variable manipulation, but its syntax differs from many other languages, leading to common pitfalls for developers transitioning to shell scripts.

0. No spaces around the equals sign

Unlike languages like Python, Bash does not allow spaces around the = when assigning a variable. Adding a space causes Bash to treat the name as a command.

name = "Yang"
# -bash: name: command not found

The correct form omits the spaces:

name="Yang"

1. Define arrays correctly

Arrays are created with parentheses and elements separated by spaces, not commas. names=("Yang" "Elon" "Bill") Using commas creates a single element containing the commas:

names=("Yang","Elon","Bill")
# results in one element: Yang,Elon,Bill

2. Choose quotes wisely

Bash treats every value as a string by default. Use no quotes when the value contains no spaces, single quotes for literal strings, and double quotes when you need variable expansion.

No quotes

Single quotes

Double quotes

Example demonstrating the difference between single and double quotes:

If truth1='${name} is amazing.' and truth2="${name} is amazing.", printing them yields:

truth1 => ${name} is amazing.
truth2 => Yang is amazing.

Thus, single quotes preserve the literal text, while double quotes allow variable expansion.

3. Avoid backticks for command substitution

Both backticks (``) and $(...) capture command output, but the latter is clearer and nests better. Use $(command) whenever possible.

file_list=`ls`
# or, preferred:
file_list=$(ls)

4. Avoid using special names

Do not name your variables the same as predefined environment variables such as USER, HOME, or PATH. Since environment variables are conventionally uppercase, using lowercase for your own variables helps avoid conflicts.