test command and [ ] syntax in Bash Scripting - Step-by-Step Execution

Concept Flow - test command and [ ] syntax

Start

↓

Evaluate condition inside test or [

↓

Condition True?

No→Return 1 (False)

Yes↓

Return 0 (True)

↓

Use return code for if/else or other logic

↓

End

The test command or [ ] evaluates a condition and returns 0 if true, 1 if false, which scripts use to decide next steps.

Execution Sample

Bash Scripting

if [ 5 -gt 3 ]; then
  echo "Yes"
else
  echo "No"
fi

This script checks if 5 is greater than 3 and prints 'Yes' if true, otherwise 'No'.

Execution Table

Step	Condition Evaluated	Result	Return Code	Branch Taken	Output
1	5 -gt 3	True	0	Then branch	Yes
2	End of if	-	-	-	-

💡 Condition 5 -gt 3 is true, so return code 0 leads to 'then' branch execution.

Variable Tracker

Variable	Start	After Step 1	Final
Return Code ($?)	-	0	0
Output	-	Yes	Yes

Key Moments - 3 Insights

Why do we use spaces around [ and ] in the condition?

Because [ and ] are commands in bash, they need spaces to separate them from the condition; see execution_table step 1 where condition is evaluated correctly only with spaces.

What does the return code 0 or 1 mean in test or [ ]?

Return code 0 means condition is true, 1 means false; scripts use this to decide which branch to run, as shown in execution_table step 1.

Can we use test and [ ] interchangeably?

Yes, test and [ ] do the same thing; [ ] requires spaces and a closing ], test does not; both return codes behave the same.

Visual Quiz - 3 Questions

Look at the execution_table step 1, what is the return code when condition '5 -gt 3' is true?

A 5

B 1

C 0

D -1

💡 Hint

Check the 'Return Code' column in execution_table row 1.

At which step does the script decide to print 'Yes'?

A Step 1

B Step 2

C Before Step 1

D No step prints 'Yes'

💡 Hint

Look at the 'Branch Taken' and 'Output' columns in execution_table row 1.

If the condition was '[ 2 -eq 3 ]', how would the return code change?

A Return code would be 0

B Return code would be 1

C Return code would be 2

D Return code would be -1

💡 Hint

Recall that return code 0 means true, 1 means false; 2 -eq 3 is false.

Concept Snapshot

test and [ ] check conditions in bash.
Return code 0 means true, 1 means false.
Spaces are required around [ and ]
Used in if statements to control flow.
Example: if [ 5 -gt 3 ]; then echo Yes; fi

Full Transcript

The test command or [ ] syntax in bash is used to check conditions. When you write a condition inside [ ], you must have spaces around the brackets because they are commands. The condition inside is evaluated, and if true, the command returns 0; if false, it returns 1. Scripts use this return code to decide which branch of code to run, like in an if statement. For example, if [ 5 -gt 3 ]; then echo Yes; else echo No; fi will print Yes because 5 is greater than 3. Remember, 0 means true, 1 means false. You can use test or [ ] interchangeably, but [ ] needs spaces and a closing bracket. This simple mechanism helps scripts make decisions based on conditions.