test

Condition evaluation.
Evaluate an expression and, if it evaluates to true, return a zero (true) exit status; otherwise return 1 (false). If there is no expression, test also returns 1 (false).

Syntax
      test expression

      [ expr ]

Key

The following primaries are used to construct expression:

     -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 (regardless of type).

     -f file       True if file exists and is a regular file.

     -g file       True if file exists and its set group ID flag is set.

     -h file       True if file exists and is a symbolic link.  This operator
                   is retained for compatibility with previous versions of
                   this program. Do not rely on its existence; use -L instead.

     -k file       True if file exists and its sticky bit is set.

     -n string     True if the length of string is nonzero.

     -p file       True if file 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 flag is set.

     -w file       True if file exists and is writable.  True indicates only
                   that the write flag is on.  The file is not writable on a
                   read-only file system even if this test indicates true.

     -x file       True if file exists and is executable.  True indicates only
                   that the execute flag is on.  If file is a directory, true
                   indicates that file can be searched.

     -z string     True if the length of string is zero.

     -L file       True if file exists and is a symbolic link.

     -O file       True if file exists and its owner matches the effective us-
                   er 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.

     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        True if string is not the null string.

     s1 = s2       True if the strings s1 and s2 are identical.

     s1 != s2      True if the strings s1 and s2 are not identical.

     s1 < s2       True if string s1 comes before s2 based on the ASCII value
                   of their characters.

     s1 > s2       True if string s1 comes after s2 based on the ASCII value
                   of their characters.

     s1            True if s1 is not the null string.

     n1 -eq n2     True if the integers n1 and n2 are algebraically equal.

     n1 -ne n2     True if the integers n1 and n2 are not algebraically equal.

     n1 -gt n2     True if the integer n1 is algebraically greater than the
                   integer n2.

     n1 -ge n2     True if the integer n1 is algebraically greater than or
                   equal to the integer n2.

     n1 -lt n2     True if the integer n1 is algebraically less than the inte-
                   ger n2.

     n1 -le n2     True if the integer n1 is algebraically less than or equal
                   to the integer n2.

     These primaries can be combined with the following operators:

     ! expression  True if expression is false.

     expression1 -a expression2
                   True if both expression1 and expression2 are true.

     expression1 -o expression2
                   True if either expression1 or expression2 are true.

     (expression)  True if expression is true.

     The -a operator has higher precedence than the -o operator.

test exits with one of the following values:

0 expression evaluated to true.
1 expression evaluated to false or expression was missing.
>1 An error occurred.

test and [ evaluate conditional expressions using a set of rules based on the number of arguments:

0 arguments - The expression is false.

1 argument - The expression is true if and only if the argument is not null.

2 arguments - If the first argument is !, the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators listed above, the expression is true if the unary test is true. If the first argument is not a valid unary conditional operator, the expression is false.

3 arguments - If the second argument is one of the binary conditional operators listed above, the result of the expression is the result of the binary test using the first and third arguments as operands.
If the first argument is !, the value is the negation of the two-argument test using the second and third arguments.
If the first argument is exactly ( and the third argument is exactly ), the result is the one-argument test of the second argument. Otherwise, the expression is false. The -a and -o operators are considered binary operators in this case.

4 arguments - If the first argument is !, the result is the negation of the three-argument expression composed of the remaining arguments. Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above.

5 or more arguments - The expression is parsed and evaluated according to precedence using the rules listed above.

Examples

$ test -a DemoFile.txt
$ echo $?
0

$ test -a NonExistentFile.txt
$ echo $?
1

$ test -n "Some sample text"
$ echo $?
0

test is a bash built in command.

“The test of a vocation is the love of the drudgery it involves” ~ Logan Pearsall

Related:

test man page - Apple.com
eval - Evaluate several commands/arguments
expr - Evaluate expressions


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