Test (Unix): Difference between revisions
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{{lowercase|title= test (Unix)}} |
{{lowercase|title= test (Unix)}} |
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'''test''' |
'''test''' isThe following functions are used to construct this parameter: |
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==Syntax== |
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test ''expression'' |
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or |
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[ ''expression'' ] |
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==Description== |
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The test command evaluates the expression parameter. In some shells (such as [[FreeBSD]] sh(1)), it is actually a shell builtin, even though external version still exists. In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces. You must test explicitly for file names in the C shell. File-name substitution (globbing) causes the shell script to exit. Functions and operators are treated as separate parameters by the test command. The expression parameter refers to a statement that is checked for a true or false condition. |
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==Functions== |
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The following functions are used to construct this parameter: |
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'''-b''' Filename - Returns a True exit value if the specified FileName exists |
'''-b''' Filename - Returns a True exit value if the specified FileName exists |
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==Exit Status== |
==Exit Status== |
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This command returns the following exit values: |
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'''0''' - The Expression parameter is true. |
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'''1''' - The Expression parameter is false or missing. |
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'''>1''' - An error occurred. |
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==Examples== |
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1. To test whether a file is nonexistent or empty, type:<!-- touch(1) -s file True if file exists and has a size greater than zero. --> |
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if test ! -s "$1" |
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then |
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echo $1 does not exist or is empty. |
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fi |
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If the file specified by the first positional parameter to the shell procedure, $1, does not exist, the test command displays an error message. If $1 exists and has a size greater than 0, the test command displays nothing. |
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Note: There must be a space between the -s function and the file name. |
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The quotation marks around $1 ensure that the test works properly even if the value of $1 is a null string. If the quotation marks are omitted and $1 is the empty string, the test command displays the error message |
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test: argument expected. |
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2. To do a complex comparison, type: |
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if [ $# -lt 2 -o ! -e "$1" ] |
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then |
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exit |
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fi |
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If the shell procedure is given fewer than two positional parameters or the file specified by $1 does not exist, then the shell procedure exits. The special shell variable $# represents the number of positional parameters entered on the command line that starts this shell procedure. |
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==See also== |
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*[[List of Unix utilities]] |
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*The [[Bash (Unix shell)|bash]] command |
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*The [[C shell|csh]] command |
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*The [[find]] command |
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*The [[korn shell|ksh]] command |
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*The [[Bourne shell|sh]] command |
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*The [[Z Shell|zsh]] command. |
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==References== |
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<!--<nowiki> |
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See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the <ref> and </ref> tags, and the template below. |
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</nowiki>--> |
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<references/> |
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{{Unix commands}} |
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[[Category:Unix SUS2008 utilities]] |
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[[Category:Conditional constructs]] |
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[[fr:Test (Unix)]] |
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[[hu:Test (Unix)]] |
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[[pl:Test (Unix)]] |
[[pl:Test (Unix)]] |
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[[ru:Test]] |
[[ru:Test]] |
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Revision as of 23:44, 3 December 2010
 | This article may need to be rewritten to comply with Wikipedia's quality standards. (May 2009) |
test isThe following functions are used to construct this parameter:
-b Filename - Returns a True exit value if the specified FileName exists and is a block special file.
Note: All remaining functions return true if the object (file or string) exists, and the condition specified is true.
-c FileName - FileName is a character special file. -d FileName - FileName is a directory. -e FileName - FileName exists. -f FileName - FileName is a regular file. -g FileName - FileName's Set Group ID bit is set. -h FileName - FileName is a symbolic link. -k FileName - FileName's sticky bit is set. -L FileName - FileName is a symbolic link. -p FileName - FileName is a named pipe (FIFO). -r FileName - FileName is readable by the current process. -s FileName - FileName has a size greater than 0. -t FileDescriptor - FileDescriptor is open and associated with a terminal. -u FileName - FileName's Set User ID bit is set.
-w FileName - FileName's write flag is on. However, the FileName will not be writable on a read-only file system even if test indicates true.
-x FileName - FileName's execute flag is on. If the specified file exists and is a directory, the True exit value indicates that the current process has permission to change (chdir) into the directory.
file1 -nt file2 - file1 is newer than file2. file1 -ot file2 - file1 is older than file2. file1 -ef file2 - file1 is another name for file2. (symbolic link or hard link)
String functions
Note that in Perl, these sections are reversed: eq is a string operator and == is a numerical operator, and so on for the others.
-n String1 - the length of the String1 variable is nonzero. -z String1 - the length of the String1 variable is 0 (zero). String1 = String2 - String1 and String2 variables are identical. String1 != String2 - String1 and String2 variables are not identical. String1 - String1 variable is not a null string.
Number functions
Integer1 -eq Integer2 - Integer1 and Integer2 variables are algebraically equal. Any of the following comparisons can be used in place of -eq. -ne (not equal) -gt (greater than) -ge (greater or equal) -lt (less than) -le (less or equal)
Operators
These functions can be combined with the following operators:
! - Unary negation operator
-a - Binary AND operator
-o - Binary OR operator (the -a operator has higher precedence
than the -o operator)
\(Expression\) - Parentheses for grouping must be escaped with a backslash (\).
The -a and -o operators, along with parentheses for grouping, are XSI extensions[1] and are therefore not portable. In portable shell scripts, the same effect may be achieved by connecting multiple invocations of test together with the && and || operators and parentheses.