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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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