# CONDITIONAL EXPRESSIONS

## File Conditionals

| Expression | Value  | What does it do? |
| ---------- | ------ | ---------------- |
| `-a`       | `file` | If file exists.
| `-b`       | `file` | If file exists and is a block special file.
| `-c`       | `file` | If file exists and is a character special file.
| `-d`       | `file` | If file exists and is a directory.
| `-e`       | `file` | If file exists.
| `-f`       | `file` | If file exists and is a regular file.
| `-g`       | `file` | If file exists and its set-group-id bit is set.
| `-h`       | `file` | If file exists and is a symbolic link.
| `-k`       | `file` | If file exists and its sticky-bit is set
| `-p`       | `file` | If file exists and is a named pipe (*FIFO*).
| `-r`       | `file` | If file exists and is readable.
| `-s`       | `file` | If file exists and its size is greater than zero.
| `-t`       | `fd`   | If file descriptor is open and refers to a terminal.
| `-u`       | `file` | If file exists and its set-user-id bit is set.
| `-w`       | `file` | If file exists and is writable.
| `-x`       | `file` | If file exists and is executable.
| `-G`       | `file` | If file exists and is owned by the effective group ID.
| `-L`       | `file` | If file exists and is a symbolic link.
| `-N`       | `file` | If file exists and has been modified since last read.
| `-O`       | `file` | If file exists and is owned by the effective user ID.
| `-S`       | `file` | If file exists and is a socket.

## File Comparisons

| Expression | What does it do? |
| ---------- | ---------------- |
| `file -ef file2` | If both files refer to the same inode and device numbers.
| `file -nt file2` | If `file` is newer than `file2` (*uses modification time*) or `file` exists and `file2` does not.
| `file -ot file2` | If `file` is older than `file2` (*uses modification time*) or `file2` exists and `file` does not.

## Variable Conditionals

| Expression | Value | What does it do? |
| ---------- | ----- | ---------------- |
| `-o`       | `opt` | If shell option is enabled.
| `-v`       | `var` | If variable has a value assigned.
| `-R`       | `var` | If variable is a name reference.
| `-z`       | `var` | If the length of string is zero.
| `-n`       | `var` | If the length of string is non-zero.

## Variable Comparisons

| Expression | What does it do? |
| ---------- | ---------------- |
| `var = var2` | Equal to.
| `var == var2` | Equal to (*synonym for `=`*).
| `var != var2` | Not equal to.
| `var < var2` | Less than (*in ASCII alphabetical order.*)
| `var > var2` | Greater than (*in ASCII alphabetical order.*)

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