test

Evaluate conditional expressions

TLDR

Check if a file exists

$ test -e [path/to/file] && echo "exists"

Check if file is a directory

$ test -d [path/to/dir] && echo "is directory"

Check if file is readable

$ test -r [path/to/file] && echo "readable"

Compare strings for equality

$ test "[string1]" = "[string2]"

Check if string is non-empty

$ test -n "[string]"

Compare integers

$ test [5] -gt [3] && echo "greater"

Combine conditions with AND

$ test -f [file] -a -r [file]

Combine conditions with OR

$ test -f [file1] -o -f [file2]

test evaluates conditional expressions, returning exit status 0 (true) or 1 (false). It is commonly used in shell scripts for decision-making in if statements and loops.The command can also be invoked as [ with a closing ] required as the last argument. This bracket syntax is more readable in conditionals: if [ -f file ]; then.Modern shells also provide [[ which offers additional features like pattern matching and safer string handling, but is not POSIX-compliant.

FILE TESTS

-e FILE

True if file exists.

-f FILE

True if file exists and is a regular file.

-d FILE

True if file exists and is a directory.

-r FILE

True if file is readable.

-w FILE

True if file is writable.

-x FILE

True if file is executable.

-s FILE

True if file exists and has size greater than zero.

-L FILE

True if file is a symbolic link.

-b FILE

True if file is a block special file.

-c FILE

True if file is a character special file.

-p FILE

True if file is a named pipe (FIFO).

-S FILE

True if file is a socket.

-g FILE

True if file has set-group-ID bit set.

-u FILE

True if file has set-user-ID bit set.

-O FILE

True if file is owned by the effective user ID.

FILE1 -nt FILE2

True if FILE1 is newer (modification date) than FILE2.

FILE1 -ot FILE2

True if FILE1 is older than FILE2.

FILE1 -ef FILE2

True if FILE1 and FILE2 refer to the same device and inode numbers.

STRING TESTS

-n STRING

True if string length is non-zero.

-z STRING

True if string length is zero.

STRING1 = STRING2

True if strings are equal.

STRING1 != STRING2

True if strings are not equal.

INTEGER COMPARISONS

INT1 -eq INT2

Equal.

INT1 -ne INT2

Not equal.

INT1 -lt INT2

Less than.

INT1 -le INT2

Less than or equal.

INT1 -gt INT2

Greater than.

INT1 -ge INT2

Greater than or equal.

OPERATORS

! EXPR

True if expression is false.

EXPR1 -a EXPR2

True if both expressions are true (AND).

EXPR1 -o EXPR2

True if either expression is true (OR).

CAVEATS

Variables in test expressions should be quoted to handle empty values and spaces correctly. The [ form requires spaces around brackets. String comparison uses = not == for POSIX compliance. Integer comparison operators (-eq, -lt) are different from string operators.

HISTORY

test is one of the original Unix utilities, dating back to Version 7 Unix in 1979. The bracket notation [ was added as an alias for improved readability in shell scripts. Both forms are specified by POSIX and available as shell builtins and standalone commands.