Linux shell 請教

Bomsori

各位先進大家好：

if [ $? -eq 0 ]

與

if [$? = 0 ]

與

if [ $# = 0 ]

究竟有何異同? 感謝指導!!

courage714

$#: Stores the number of command-line arguments that
      were passed to the shell program.
$?: Stores the exit value of the last command that was
      executed.
arg1 -eq arg2: like the set of "-eq, -ne, -lt, -le, -gt, or -ge", they are arithmetic binary operators. The
                        arguments may  be positive or negative integers.
str1 = str2:    POSIX compliant string test command, arguments will be interpreted as string
str1 == str2 : the same as "str1 = str2"

Bomsori

courage714 发表于 2020-5-12 17:50
$#: Stores the number of command-line arguments that
      were passed to the shell program.
$?: St ...

ok, thanks.

So what is the difference when 0 is as string and argument?

courage714

The part $? and 0 in the statement if [ $? = 0 ]  would be transferred to  "$?" and "0" and be stored as string  underneath some shell script interpreters like bash or csh. But unfortunately it cannot be supported by all shell script interpreters. So normally I would rather use either  if [ $? -eq 0 ] or if [  "$?" = "0" ]

wyfme

学习

Bomsori

courage714 发表于 2020-5-12 18:37
The part $? and 0 in the statement if [ $? = 0 ]  would be transferred to  "$?" and "0" and be store ...

Hi ,

Thanks again for the explanation.
I think it is good enough to let me pass EX300 exam for RHCE.

Regards,
Bomsori