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# Bash Older Than
The `-ot` (older than) operator is a binary file test operator in Bash used within conditional expressions to compare the modification timestamps (`mtime`) of two files. It evaluates to true (returns exit status `0`) if the first file is strictly older than the second file, or if the second file exists but the first file does not.
## Syntax
The operator can be used with the Bash `test` builtin (`[ ]`) or the Bash extended test keyword (`[[ ]]`). Note that `-ot` is a Bash/Ksh extension and is not part of the POSIX standard; it should not be relied upon for strictly portable POSIX `sh` scripts.
```bash theme={"dark"}
[ file1 -ot file2 ]
# or
[[ file1 -ot file2 ]]
```
## Evaluation Matrix
The operator resolves the comparison based on file existence and the `mtime` metadata retrieved via the `stat` system call. It returns false (exit status `1`) in any scenario not explicitly evaluating to true.
| State of `file1` | State of `file2` | Evaluation Result |
| :--------------- | :--------------- | :----------------------------------------------------------------------------------------------- |
| Exists | Exists | **True** if `file1` `mtime` \< `file2` `mtime`. **False** if `file1` `mtime` >= `file2` `mtime`. |
| Does not exist | Exists | **True** |
| Exists | Does not exist | **False** |
| Does not exist | Does not exist | **False** |
## Technical Characteristics
* **Strict Inequality:** The comparison is strictly "older than". If both files have the exact same modification timestamp, the operator evaluates to false.
* **Symlink Dereferencing:** The `-ot` operator automatically dereferences symbolic links. It compares the `mtime` of the ultimate target files, not the timestamps of the symlinks themselves. If a symlink points to a non-existent file (a broken link), it is treated as a non-existent file.
* **Timestamp Precision:** In Bash 5.0 and later, running on modern filesystems (like ext4, xfs, or zfs), the `-ot` operator utilizes sub-second (nanosecond) precision (`st_mtim`) for its comparisons. In Bash 4.4 and earlier, or on legacy filesystems, the comparison is truncated to the nearest second (`st_mtime`).
* **Metadata Scope:** The operator strictly evaluates the modification time (`mtime`), which updates when file contents change. It does not evaluate the change time (`ctime`, metadata changes) or access time (`atime`).
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