test / [ / [[ - Conditional Expressions

Evaluate conditional expressions.

Source: src/scripting/test_builtin.f90:execute_test_command

Synopsis

test expression
[ expression ]
[[ expression ]]

Description

Evaluates a conditional expression and returns an exit status of 0 (true) or 1 (false). The [ command is identical to test but requires a closing ]. The [[ command is an extended test with additional features.

File Tests

String Tests

Numeric Tests

File Comparison

Logical Operators (test / [)

Extended Test [[ ]]

The [[ command provides additional features:

Pattern Matching

[[ $string == pattern ]]   # Glob pattern match
[[ $string != pattern ]]   # Glob pattern not match

Regex Matching

[[ $string =~ regex ]]     # POSIX extended regex
[[ $string !~ regex ]]     # Regex not match

Capture groups are stored in BASH_REMATCH:

• ${BASH_REMATCH[0]} - Full match
• ${BASH_REMATCH[1]} - First capture group
• etc.

Logical Operators in [[

[[ expr1 && expr2 ]]   # Logical AND (short-circuit)
[[ expr1 || expr2 ]]   # Logical OR (short-circuit)
[[ ! expr ]]           # Logical NOT

Return Value

Examples

File tests

if [ -f /etc/passwd ]; then
    echo "File exists"
fi

if [[ -d "$HOME" && -w "$HOME" ]]; then
    echo "Home exists and is writable"
fi

String tests

name="fortsh"

if [ -n "$name" ]; then
    echo "Name is set"
fi

if [ "$name" = "fortsh" ]; then
    echo "It's fortsh!"
fi

Numeric tests

count=5

if [ "$count" -gt 0 ]; then
    echo "Count is positive"
fi

if [[ $count -ge 1 && $count -le 10 ]]; then
    echo "Count is between 1 and 10"
fi

Regex matching

email="user@example.com"

if [[ $email =~ ^[a-z]+@[a-z]+\.[a-z]+$ ]]; then
    echo "Valid email format"
fi

# With capture groups
version="v1.2.3"
if [[ $version =~ ^v([0-9]+)\.([0-9]+)\.([0-9]+)$ ]]; then
    echo "Major: ${BASH_REMATCH[1]}"
    echo "Minor: ${BASH_REMATCH[2]}"
    echo "Patch: ${BASH_REMATCH[3]}"
fi

Pattern matching

file="script.sh"

if [[ $file == *.sh ]]; then
    echo "Shell script"
fi

if [[ $file == script.* ]]; then
    echo "A script file"
fi

Implementation Details

From test_builtin.f90:

! File test operators
case ("-e")
    call stat_file(path, stat_result, errno)
    result = (errno == 0)
case ("-f")
    result = is_regular_file(path)
case ("-d")
    result = is_directory(path)

The regex matching uses POSIX extended regular expressions:

! Extended test: regex match with =~
if (extended .and. operator == "=~") then
    call regex_match(left_operand, right_operand, matched, captures)
    if (matched) then
        ! Store captures in BASH_REMATCH array
        call set_bash_rematch(captures)
    end if
end if

Differences Between [ ] and [[ ]]

Related Commands

• if - Conditional execution
• case - Pattern matching

Notes

• For portability, use [ ] with -a and -o operators
• [[ ]] is preferred for complex conditions due to cleaner syntax
• Always quote variables in [ ] to prevent word splitting: [ "$var" = "value" ]
• In [[ ]], quoting is optional for variables: [[ $var == value ]]