test Command
Intermediate Shell Scripting man(1)Evaluate conditional expressions for scripting
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📅 Updated: Apr 30, 2026
SYNTAX
test EXPRESSION
What Does test Do?
test evaluates conditional expressions and returns an exit status of 0 (true) or 1 (false). It is the foundation of if statements and conditional logic in shell scripts.
test can be written as test expression or [ expression ] (the bracket syntax). Bash also provides [[ expression ]] which is more powerful and safer (it handles word splitting and glob expansion better).
test supports file tests (-f, -d, -r, -w, -x), string comparisons (=, !=, -z, -n), numeric comparisons (-eq, -ne, -lt, -gt), and logical operators (-a, -o, !).
test can be written as test expression or [ expression ] (the bracket syntax). Bash also provides [[ expression ]] which is more powerful and safer (it handles word splitting and glob expansion better).
test supports file tests (-f, -d, -r, -w, -x), string comparisons (=, !=, -z, -n), numeric comparisons (-eq, -ne, -lt, -gt), and logical operators (-a, -o, !).
Options & Flags
| Option | Description | Example |
|---|---|---|
| -f | True if file exists and is a regular file | test -f /etc/passwd && echo "exists" |
| -d | True if directory exists | [ -d /var/log ] && echo "exists" |
| -e | True if file exists (any type) | [ -e /path/to/file ] |
| -r/-w/-x | True if file is readable/writable/executable | [ -x /usr/bin/python3 ] |
| -z | True if string is empty | [ -z "$VAR" ] && echo "empty" |
| -n | True if string is non-empty | [ -n "$NAME" ] && echo "set" |
| -eq/-ne/-lt/-gt | Numeric comparisons | [ "$count" -gt 10 ] && echo "more than 10" |
| = | String equality | [ "$answer" = "yes" ] |
Practical Examples
#1 Check if file exists
Tests if config.yml exists and is a regular file.
$ [ -f config.yml ] && echo "Config found" || echo "Config missing"#2 Check directory
Tests if the directory exists.
$ [ -d /var/www ] && echo "Directory exists"#3 Numeric comparison
Compares numbers using -gt (greater than).
$ count=15; [ $count -gt 10 ] && echo "More than 10"
Output:
More than 10
#4 String comparison
Checks if the current user is root.
$ [ "$USER" = "root" ] && echo "Running as root"#5 Empty string check
Tests if a variable is empty or unset.
$ [ -z "$API_KEY" ] && echo "API_KEY not set!"#6 Complex condition
Checks if file exists AND is executable using bash [[ syntax.
$ [[ -f app.py && -x app.py ]] && echo "Executable Python script"#7 If statement
Uses test in an if statement for conditional logic.
$ if [ -r /etc/shadow ]; then echo "Can read shadow"; else echo "No access"; fiTips & Best Practices
Always quote variables: Use [ "$var" = "value" ] with quotes. Without quotes, empty variables cause syntax errors: [ = value ] fails.
[[ vs [ in bash: [[ is bash-specific but safer — it handles empty variables and supports regex (=~) and glob (*) matching. Prefer [[ in bash scripts.
Spaces are required: [ and ] need spaces: [ -f file ] is correct. [-f file] or [ -f file] will fail. The brackets are actually commands.
Frequently Asked Questions
How do I check if a file exists in bash?
Use [ -f filename ] for regular files, [ -d dirname ] for directories, [ -e path ] for any type. Always quote variables.
How do I compare numbers in bash?
Use -eq (equal), -ne (not equal), -lt (less than), -gt (greater than), -le (less or equal), -ge (greater or equal).
What is the difference between [ ] and [[ ]]?
[ ] is POSIX-standard (works everywhere). [[ ]] is bash-specific but supports regex, glob, and handles empty variables better.
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