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Test Function

Debian 'Test' man page

    The Bash Test Function...

       [ + space + expression + space + ]

    Test is used to check out a string, number or a file. The only output of test is it's exit status. If it returns 0 the test is sucessful, any other number is a failure.

    The syntax comes in two forms:

    • test expression
    • [ expression ]

    The spaces between the expression and the brackets are required.

    CREATED 2012-11-17 03:32:48.0


    UPDATED 2012-11-18 18:12:29.0

    Test Options...

    Examples follow but first a list of common test options:

    -d file True if <file> is a directory
    -e file True if <file> exists
    -f file True if <file> exists and is a file
    -h file True if <file> exists and is a symbolik link
    -L file True is <file> is a symbolic link
    -r file True is <file> is readable by you (the current user)
    -w file True if <file> is writable by you
    -x file True if <file> is executable by you
    file1 -nt file2 True if <file1> is newer than <file2>
    file1 -ot file2 True if <file1> is older than <file2>
    -z string True if <string> is empty
    -n string True if <string> is not empty
    string1 = string2 True if <string1> equals <string2>
    string1 != string2 True if <string1> is not equal to <string2>

    CREATED 2017-04-11 03:57:13.0


    UPDATED 2017-04-11 03:57:22.0



    The -f flag tests for the existance of a file. Remember there are two ways of executing a test. [ <option> <arg>]. (Don't forget the spaces around the brackets)

    if [ -f myfile.txt ]

    CREATED 2012-11-18 18:21:33.0


    UPDATED 2017-04-11 04:38:09.0

    Logicel AND and OR...

    The && (logical AND) and || (logical OR) can be used to string two test cases together in a single statement:

    if [ -f "$myfile" ] && [ -r "$myfile" ]
       <write to file>

    However later versions of test offer two other options -a for AND and -o for OR:

    if [ -f "$myfile" -a -r "$myfile" ]
       <write to file>

    Both of these do the same thing. However, && and || operate at the shell level where -a and -o operate within the test command. Also -a and -i don't short circut.

    CREATED 2017-04-11 04:48:58.0


    UPDATED 2017-04-11 04:49:10.0


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