测试字符串

尽可能使用引用，而不是过滤字符串。 Bash 足以在测试中处理空字符串。所以，请使用空（非空）字符串测试，而不是填充字符，使得代码更易于阅读。

# Do this:
if [[ "${my_var}" = "some_string" ]]; then
  do_something
fi

# -z (string length is zero) and -n (string length is not zero) are
# preferred over testing for an empty string
if [[ -z "${my_var}" ]]; then
  do_something
fi

# This is OK (ensure quotes on the empty side), but not preferred:
if [[ "${my_var}" = "" ]]; then
  do_something
fi

# Not this:
if [[ "${my_var}X" = "some_stringX" ]]; then
  do_something
fi

为了避免对你测试的目的产生困惑，请明确使用-z或者-n

# Use this
if [[ -n "${my_var}" ]]; then
  do_something
fi

# Instead of this as errors can occur if ${my_var} expands to a test
# flag
if [[ "${my_var}" ]]; then
  do_something
fi