test Command Cheat Sheet

test checks file types and compares values. It returns a 0 exit status for true and 1 for false. It is arguably the most used command in shell scripting, often seen as [ ].

Synopsis

test EXPRESSION
[ EXPRESSION ]

File Tests

Flag	Description
`-e FILE`	Exists
`-f FILE`	Exists and is a regular file
`-d FILE`	Exists and is a directory
`-s FILE`	Exists and size > 0
`-r FILE`	Readable
`-w FILE`	Writable
`-x FILE`	Executable
`-L FILE`	Symbolic link

if [ -d "/etc" ]; then
    echo "/etc is a directory"
fi

String Comparators

Operator	Description
`-z STRING`	Length is zero (Empty)
`-n STRING`	Length is non-zero (Not empty)
`STR1 = STR2`	Equal
`STR1 != STR2`	Not equal

if [ -z "$VAR" ]; then
    echo "Variable matches empty string"
fi

Integer Comparators

Operator	Description
`-eq`	Equal
`-ne`	Not Equal
`-gt`	Greater Than
`-ge`	Greater or Equal
`-lt`	Less Than
`-le`	Less or Equal

if [ "$COUNT" -gt 10 ]; then
    echo "Count is greater than 10"
fi

Note: These only work for integers.

Logical Operators

Operator	Description
`! EXPR`	NOT
`EXP1 -a EXP2`	AND (Standard `[ ]` syntax)
`EXP1 -o EXP2`	OR (Standard `[ ]` syntax)

if [ -f "file.txt" -a -w "file.txt" ]; then
    echo "File exists AND is writable"
fi

[ ] vs [[ ]]

test is synonymous with [ ... ]. Bash introduces [[ ... ]], which is safer and more powerful.

[[ ]] supports && and || instead of -a and -o.
[[ ]] supports glob matching (=~).
[[ ]] handles variables with spaces better.

Recommendation: Use [[ ... ]] in Bash scripts, and [ ... ] (the test command) only for POSIX sh compatibility.