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SEREGA PRIVET$ unset A
SEREGA PRIVET$ [ $A != "" ]; echo $?
bash: [: !=: unary operator expected
2
SEREGA PRIVET$ [ x$A != x"" ]; echo $?
1
SEREGA PRIVET$ [ $A = "" ]; echo $?
bash: [: =: unary operator expected
2
SEREGA PRIVET$ [ x$A = x"" ]; echo $?
0аᶘ
x просто всегда использовать кавычки?F
x просто всегда использовать кавычки?аᶘ
F
F
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[ -n "$string" -o "$a" = "$b" ] may cause an error with some versions of Bash if $string is empty. The safe way is to append an extra character to possibly empty variables, [ "x$string" != x -o "x$a" = "x$b" ] (the "x's" cancel out).аᶘ
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SEREGA PRIVET$ unset A
SEREGA PRIVET$ [ $A != "" ]; echo $?
bash: [: !=: unary operator expected
2
SEREGA PRIVET$ [ x$A != x"" ]; echo $?
1
SEREGA PRIVET$ [ $A = "" ]; echo $?
bash: [: =: unary operator expected
2
SEREGA PRIVET$ [ x$A = x"" ]; echo $?
0user@user-PC:~$ unset q; [ $q ]; echo $?
1
user@user-PC:~$ unset q; ! [ $q ]; echo $?
0
F
user@user-PC:~$ unset q; [ $q ]; echo $?
1
user@user-PC:~$ unset q; ! [ $q ]; echo $?
0
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