06-14-2009
Equivalence of test, /usr/bin/test, [ ], and /usr/bin/[
these are commands and you can only use one of them:-
examples:-
if test -z "$1"
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo
if /usr/bin/test -z "$1" # Equivalent to "test" builtin.
# ^^^^^^^^^^^^^ # Specifying full pathname.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo
if [ -z "$1" ] # Functionally identical to above code blocks.
# if [ -z "$1" should work, but...
#+ Bash responds to a missing close-bracket with an error message.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
if /usr/bin/[ -z "$1" ] # Again, functionally identical to above.
# if /usr/bin/[ -z "$1" # Works, but gives an error message.
# # Note:
# This has been fixed in Bash, version 3.x.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
Finally:-
The [[ ]] construct is the more versatile Bash version of [ ]. This is the extended test command, adopted from
ksh88.
No filename expansion or word splitting takes place between [[ and ]], but there is parameter expansion
and command substitution.
file=/etc/passwd
if [[ -e $file ]]
then
echo "Password file exists."
fi
Using the [[ ... ]] test construct, rather than [ ... ] can prevent many logic errors in scripts. For example,
the &&, ||, <, and > operators work within a [[ ]] test, despite giving an error within a [ ] construct.
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test(1B) SunOS/BSD Compatibility Package Commands test(1B)
NAME
test - condition evaluation command
SYNOPSIS
/usr/ucb/test expression
expression
DESCRIPTION
test evaluates the expression expression and, if its value is true, sets 0 (true) exit status; otherwise, a non-zero (false) exit status
is set. test also sets a non-zero exit status if there are no arguments. When permissions are tested, the effective user ID of the process
is used.
All operators, flags, and brackets (brackets used as shown in the second SYNOPSIS line) must be separate arguments to the test command;
normally these items are separated by spaces.
USAGE
Primitives
The following primitives are used to construct expression:
-r filename True if filename exists and is readable.
-w filename True if filename exists and is writable.
-x filename True if filename exists and is executable.
-f filename True if filename exists and is a regular file. Alternatively, if /usr/bin/sh users specify /usr/ucb before /usr/bin in
their PATH environment variable, then test will return true if filename exists and is (not-a-directory). This is also the
default for /usr/bin/csh users.
-d filename True if filename exists and is a directory.
-c filename True if filename exists and is a character special file.
-b filename True if filename exists and is a block special file.
-p filename True if filename exists and is a named pipe (fifo).
-u filename True if filename exists and its set-user- ID bit is set.
-g filename True if filename exists and its set-group- ID bit is set.
-k filename True if filename exists and its sticky bit is set.
-s filename True if filename exists and has a size greater than zero.
-t[ fildes ] True if the open file whose file descriptor number is fildes (1 by default) is associated with a terminal device.
-z s1 True if the length of string s1 is zero.
-n s1 True if the length of the string s1 is non-zero.
s1 = s2 True if strings s1 and s2 are identical.
s1 != s2 True if strings s1 and s2 are not identical.
s1 True if s1 is not the null string.
n1 -eq n2 True if the integers n1 and n2 are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, and -le may be used in
place of -eq.
Operators
These primaries may be combined with the following operators:
! Unary negation operator.
-a Binary and operator.
-o Binary or operator (-a has higher precedence than -o).
(expression) Parentheses for grouping. Notice also that parentheses are meaningful to the shell and, therefore, must be quoted.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWscpu |
+-----------------------------+-----------------------------+
SEE ALSO
find(1), sh(1), attributes(5)
NOTES
The not-a-directory alternative to the -f option is a transition aid for BSD applications and may not be supported in future releases.
If you test a file you own (the -r , -w , or -x tests), but the permission tested does not have the owner bit set, a non-zero (false) exit
status will be returned even though the file may have the group or other bit set for that permission. The correct exit status will be set
if you are super-user.
The = and != operators have a higher precedence than the -r through -n operators, and = and != always expect arguments; therefore, = and !=
cannot be used with the -r through -n operators.
If more than one argument follows the -r through -n operators, only the first argument is examined; the others are ignored, unless a -a or
a -o is the second argument.
SunOS 5.10 1 Apr 1996 test(1B)