test

Check if a file exists

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

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

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

$ test "[string1]" = "[string2]"

$ test -n "[string]"

$ test [5] -gt [3] && echo "greater"

$ test -f [file] -a -r [file]

$ test -f [file1] -o -f [file2]

test EXPRESSION
[ EXPRESSION ]

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.

-e FILE

True if file exists.

True if file exists and is a regular file.

True if file exists and is a directory.

True if file is readable.

True if file is writable.

True if file is executable.

True if file exists and has size greater than zero.

True if file is a symbolic link.

-n STRING

True if string length is non-zero.

True if string length is zero.

True if strings are equal.

True if strings are not equal.

INT1 -eq INT2

Equal.

Not equal.

Less than.

Less than or equal.

Greater than.

Greater than or equal.

! EXPR

True if expression is false.

True if both expressions are true (AND).

True if either expression is true (OR).

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.

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.

bash(1), sh(1), expr(1)