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Full Discussion: test condition
Top Forums Shell Programming and Scripting test condition Post 302264227 by radoulov on Wednesday 3rd of December 2008 01:25:51 PM
Old 12-03-2008
The shell keyword [[ requires a different syntax,
see below.

With bash:

Code:
$ type [[ 
[[ is a shell keyword
$ help [[
[[ ... ]]: [[ expression ]]
    Returns a status of 0 or 1 depending on the evaluation of the conditional
    expression EXPRESSION.  Expressions are composed of the same primaries used
    by the `test' builtin, and may be combined using the following operators
    
        ( EXPRESSION )  Returns the value of EXPRESSION
        ! EXPRESSION    True if EXPRESSION is false; else false
        EXPR1 && EXPR2  True if both EXPR1 and EXPR2 are true; else false
        EXPR1 || EXPR2  True if either EXPR1 or EXPR2 is true; else false
    
    When the `==' and `!=' operators are used, the string to the right of the
    operator is used as a pattern and pattern matching is performed.  The
    && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
    determine the expression's value.

So:

Code:
$ [ x = x -a x = x ] && echo ok
ok
$ [[ x = x -a x = x ]] && echo ok
bash: syntax error in conditional expression
bash: syntax error near `-a'

But:

Code:
$ [[ x == x && x == x ]] && echo ok
ok

 

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LEARN ABOUT X11R4

test

TEST(1)                                                            User Commands                                                           TEST(1)

NAME

       test - check file types and compare values

SYNOPSIS

       test EXPRESSION
       test

       [ EXPRESSION ]
       [ ]
       [ OPTION

DESCRIPTION

       Exit with the status determined by EXPRESSION.

       --help display this help and exit

       --version
              output version information and exit

       An omitted EXPRESSION defaults to false.  Otherwise, EXPRESSION is true or false and sets exit status.  It is one of:

       ( EXPRESSION )
              EXPRESSION is true

       ! EXPRESSION
              EXPRESSION is false

       EXPRESSION1 -a EXPRESSION2
              both EXPRESSION1 and EXPRESSION2 are true

       EXPRESSION1 -o EXPRESSION2
              either EXPRESSION1 or EXPRESSION2 is true

       -n STRING
              the length of STRING is nonzero

       STRING equivalent to -n STRING

       -z STRING
              the length of STRING is zero

       STRING1 = STRING2
              the strings are equal

       STRING1 != STRING2
              the strings are not equal

       INTEGER1 -eq INTEGER2
              INTEGER1 is equal to INTEGER2

       INTEGER1 -ge INTEGER2
              INTEGER1 is greater than or equal to INTEGER2

       INTEGER1 -gt INTEGER2
              INTEGER1 is greater than INTEGER2

       INTEGER1 -le INTEGER2
              INTEGER1 is less than or equal to INTEGER2

       INTEGER1 -lt INTEGER2
              INTEGER1 is less than INTEGER2

       INTEGER1 -ne INTEGER2
              INTEGER1 is not equal to INTEGER2

       FILE1 -ef FILE2
              FILE1 and FILE2 have the same device and inode numbers

       FILE1 -nt FILE2
              FILE1 is newer (modification date) than FILE2

       FILE1 -ot FILE2
              FILE1 is older than FILE2

       -b FILE
              FILE exists and is block special

       -c FILE
              FILE exists and is character special

       -d FILE
              FILE exists and is a directory

       -e FILE
              FILE exists

       -f FILE
              FILE exists and is a regular file

       -g FILE
              FILE exists and is set-group-ID

       -G FILE
              FILE exists and is owned by the effective group ID

       -h FILE
              FILE exists and is a symbolic link (same as -L)

       -k FILE
              FILE exists and has its sticky bit set

       -L FILE
              FILE exists and is a symbolic link (same as -h)

       -O FILE
              FILE exists and is owned by the effective user ID

       -p FILE
              FILE exists and is a named pipe

       -r FILE
              FILE exists and read permission is granted

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t FD  file descriptor FD is opened on a terminal

       -u FILE
              FILE exists and its set-user-ID bit is set

       -w FILE
              FILE exists and write permission is granted

       -x FILE
              FILE exists and execute (or search) permission is granted

       Except for -h and -L, all FILE-related tests dereference symbolic links.  Beware that parentheses need to be escaped (e.g., by backslashes)
       for shells.  INTEGER may also be -l STRING, which evaluates to the length of STRING.

       NOTE: Binary -a and -o are inherently ambiguous.  Use 'test EXPR1 && test EXPR2' or 'test EXPR1 || test EXPR2' instead.

       NOTE: [ honors the --help and --version options, but test does not.  test treats each of those as it treats any other nonempty STRING.

       NOTE: your shell may have its own version of test and/or [, which usually supersedes the version described  here.   Please  refer  to  your
       shell's documentation for details about the options it supports.

AUTHOR

       Written by Kevin Braunsdorf and Matthew Bradburn.

REPORTING BUGS

       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report [ translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2017 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       Full documentation at: <http://www.gnu.org/software/coreutils/[>
       or available locally via: info '(coreutils) test invocation'

GNU coreutils 8.28                                                 January 2018                                                            TEST(1)
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