test command and [ ] syntax in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the test command do in bash scripting?

The test command checks conditions like file existence or string comparison and returns true or false based on the result.

beginner

How is the [ ] syntax related to the test command?

The [ ] syntax is a shorthand for the test command. For example, [ -f file ] is the same as test -f file.

beginner

What is the correct way to check if a file exists using [ ]?

Use [ -e filename ]. It returns true if the file exists, false otherwise.

intermediate

Why must there be spaces around the brackets in [ ]?

Because [ and ] are separate commands and arguments. Without spaces, bash treats it as one word and errors occur.

beginner

How do you check if two strings are equal using test or [ ]?

Use [ "$str1" = "$str2" ] or test "$str1" = "$str2". Quotes prevent errors if strings are empty or contain spaces.

What does [ -d /home/user ] check?

A If /home/user is a file

B If /home/user is empty

C If /home/user is a directory

D If /home/user is writable

-d checks if the path is a directory.

Which is the correct way to check if variable var is empty?

A Both A and D

B [ -n "$var" ]

C [ -z "$var" ]

D [ "$var" = "" ]

-z checks if string length is zero. Comparing to empty string also works.

What happens if you write [ -f file] without space before ]?

A It works fine

B Syntax error occurs

C It checks if file is executable

D It checks if file is a directory

Missing space before ] causes bash to misinterpret the command and throw a syntax error.

Which command is equivalent to [ "$a" = "$b" ]?

A test "$a" = "$b"

B test $a == $b

C test $a = $b

D test "$a" != "$b"

Quotes are needed to handle empty or spaced strings. Single equals = is used for string comparison.

What does test -e filename check?

A If filename is empty

B If filename is executable

C If filename is a directory

D If filename exists

-e checks if the file or directory exists.

Explain how to use the test command and [ ] syntax to check if a file exists and is a directory.

Think about the options for file tests and how [ ] is a shortcut for test.

Describe common mistakes when using [ ] in bash scripts and how to avoid them.

Focus on spacing and quoting to prevent errors.