Executable Check

The -x operator is a unary file test operator in Bash used to evaluate whether a specified file exists and whether the current user has execute permissions for it. It returns an exit status of 0 (true) if both conditions are met, and 1 (false) otherwise.

Syntax

The operator requires a single string operand representing the file path. It can be invoked using the test builtin, the POSIX test command [ ], or the Bash extended test keyword [[ ]].

test -x /path/to/file
[ -x /path/to/file ]
[[ -x /path/to/file ]]

Evaluation Mechanics

• Effective Permissions: The operator evaluates permissions based on the effective user ID (eUID) and effective group ID (eGID) of the process executing the script, rather than the real user ID.
• Directory Traversal: When the operand is a directory, the -x operator evaluates the “search” bit. A true result indicates the current user has permission to traverse into the directory to access its contents.
• Symbolic Links: The -x operator dereferences symbolic links. It evaluates the existence and permissions of the ultimate target file, not the symlink itself.
• Root Execution: If the eUID is 0 (root), the -x operator evaluates to true for regular files if the execute bit is set for any class (user, group, or other) in the file’s mode bits. If a regular file has no execute bits set at all, it evaluates to false. However, for directories, -x always evaluates to true for root, as root inherently possesses directory search permissions regardless of the mode bits (e.g., even with mode 000).
• Access Control Lists (ACLs): The operator respects filesystem ACLs. It queries the operating system’s access control mechanisms (e.g., via the faccessat or access system calls) rather than strictly parsing the standard POSIX rwx mode bits.

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