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Conditional Expressions

A conditional expression is used with the [[ compound command to test attributes of files and to compare strings. Each expression can be constructed from one or more of the following unary or binary expressions:

-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 has its setgid bit set.
-h file
true if file exists and is a symbolic link.
-k file
true if file exists and has its sticky bit set.
-n string
true if length of string is non-zero.
-o option
true if option named option is on. option may be a single character, in which case it is a single letter option name. (See section Specifying Options.)
-p file
true if file exists and is a FIFO special file (named pipe).
-r file
true if file exists and is readable by current process.
-s file
true if file exists and has size greater than zero.
-t fd
true if file descriptor number fd is open and associated with a terminal device. (note: fd is not optional)
-u file
true if file exists and has its setuid bit set.
-w file
true if file exists and is writable by current process.
-x file
true if file exists and is executable by current process. If file exists and is a directory, then the current process has permission to search in the directory.
-z string
true if length of string is zero.
-L file
true if file exists and is a symbolic link.
-O file
true if file exists and is owned by the effective user ID of this process.
-G file
true if file exists and its group matches the effective group ID of this process.
-S file
true if file exists and is a socket.
-N file
true if file exists and its access time is not newer than its modification time.
file1 -nt file2
true if file1 exists and is newer than file2.
file1 -ot file2
true if file1 exists and is older than file2.
file1 -ef file2
true if file1 and file2 exist and refer to the same file.
string = pattern
string == pattern
true if string matches pattern. The `==' form is the preferred one. The `=' form is for backward compatibility and should be considered obsolete.
string != pattern
true if string does not match pattern.
string1 < string2
true if string1 comes before string2 based on ASCII value of their characters.
string1 > string2
true if string1 comes after string2 based on ASCII value of their characters.
exp1 -eq exp2
true if exp1 is numerically equal to exp2.
exp1 -ne exp2
true if exp1 is numerically not equal to exp2.
exp1 -lt exp2
true if exp1 is numerically less than exp2.
exp1 -gt exp2
true if exp1 is numerically greater than exp2.
exp1 -le exp2
true if exp1 is numerically less than or equal to exp2.
exp1 -ge exp2
true if exp1 is numerically greater than or equal to exp2.
( exp )
true if exp is true.
! exp
true if exp is false.
exp1 && exp2
true if exp1 and exp2 are both true.
exp1 || exp2
true if either exp1 or exp2 is true.

In each of the above expressions, if file is of the form `/dev/fd/n', where n is an integer, then the test applied to the open file whose descriptor number is n, even if the underlying system does not support the /dev/fd directory.


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