[SGVLUG] bash scripting - checking for file existence

[John E. Kreznar]

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> if [ -e ]; then echo true; else echo false; fi
> # this prints true, shouldn't it be a syntax error?

man bash clarifies this case:

              test and [ evaluate conditional expressions using a set
              of rules based on the number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the
                     argument is not null.
              2 arguments
                     If the first argument is !, the expression is
                     true if and only if the second argument is null.
                     If the first argument is one of the unary
                     conditional operators listed above under
                     CONDITIONAL EXPRESSIONS, the expression is true
                     if the unary test is true.  If the first argument
                     is not a valid unary conditional operator, the
                     expression is false.

In " [ -e ] " there is only one argument and it's not null, so the
expression is true.

Superficial tests of dash and ash suggest that they behave the same as
bash.  So I installed tcsh (on a throw-away virtual machine, not
wanting to clutter one of my working machines), and the results again
appear to be the same:

   throw-away:~# echo $FILE | od -t x1 | head -1
   0000000 0a
   throw-away:~# [ -e $FILE ] ; echo $?
   0
   throw-away:~# [ -e "$FILE" ] ; echo $?
   1
   throw-away:~# [ -e "" ] ; echo $?
   1

??

- -- 
 John E. Kreznar jek at ininx.com 9F1148454619A5F08550 705961A47CC541AFEF13

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