Examples
1. To test whether a file is nonexistent or empty, type:
if test ! -s "$1" then echo $1 does not exist or is empty. fiIf the file specified by the first positional parameter to the shell procedure, $1, does not exist or is of size 0, the test command displays the message. If $1 exists and has a size greater than 0, the test command displays nothing.
Note: There must be a space between the -s function and the file name.
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
test: argument expected.2. To do a complex comparison, type:
if then exit fiIf 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.
Read more about this topic: Test (Unix)
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