Bash Conditional Expressions

Bash Reference Manual. Node: Bash Conditional Expressions

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5.6: Bash Conditional Expressions

Conditional expressions are used by the [[ compound command and the test and [ builtin commands.

Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. If any file argument to one of the primaries is of the form `/dev/fd/N', then file descriptor N is checked.

`-a file`	True if `file` exists.
`-b file`	True if `file` exists and is a block special file.
`-c file`	True if `file` exists and is a character special file.
`-d file`	True if `file` exists and is a directory.
`-e file`	True if `file` exists.
`-f file`	True if `file` exists and is a regular file.
`-g file`	True if `file` exists and its set-group-id bit is set.
`-h file`	True if `file` exists and is a symbolic link.
`-k file`	True if `file` exists and its "sticky" bit is set.
`-p file`	True if `file` exists and is a named pipe (FIFO).
`-r file`	True if `file` exists and is readable.
`-s file`	True if `file` exists and has a size greater than zero.
`-t fd`	True if file descriptor `fd` is open and refers to a terminal.
`-u file`	True if `file` exists and its set-user-id bit is set.
`-w file`	True if `file` exists and is writable.
`-x file`	True if `file` exists and is executable.
`-O file`	True if `file` exists and is owned by the effective user id.
`-G file`	True if `file` exists and is owned by the effective group id.
`-L file`	True if `file` exists and is a symbolic link.
`-S file`	True if `file` exists and is a socket.
`-N file`	True if `file` exists and has been modified since it was last read.
`file1 -nt file2`	True if `file1` is newer (according to modification date) than `file2`.
`file1 -ot file2`	True if `file1` is older than `file2`.
`file1 -ef file2`	True if `file1` and `file2` have the same device and inode numbers.
`-o optname`	True if shell option `optname` is enabled. The list of options appears in the description of the ``-o`' option to the `set` builtin (see The Set Builtin).
`-z string`	True if the length of `string` is zero.
`-n string` `string`	True if the length of `string` is non-zero.
`string1 == string2`	True if the strings are equal. ``=`' may be used in place of ``==`'.
`string1 != string2`	True if the strings are not equal.
`string1 < string2`	True if `string1` sorts before `string2` lexicographically in the current locale.
`string1 > string2`	True if `string1` sorts after `string2` lexicographically in the current locale.
`arg1 OP arg2`	`OP` is one of ``-eq`', ``-ne`', ``-lt`', ``-le`', ``-gt`', or ``-ge`'. These arithmetic binary operators return true if `arg1` is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to `arg2`, respectively. `Arg1` and `arg2` may be positive or negative integers.

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