ex11.sh

Shall高级编程

#!/bin/bash

echo

if test -z "$1"
then
  echo "No command-line arguments."
else
  echo "First command-line argument is $1."
fi

echo

if /usr/bin/test -z "$1"      # Equivalent to "test" builtin.
#  ^^^^^^^^^^^^^              # Specifying full pathname.
then
  echo "No command-line arguments."
else
  echo "First command-line argument is $1."
fi

echo

if [ -z "$1" ]                # Functionally identical to above code blocks.
#   if [ -z "$1"                should work, but...
#+  Bash responds to a missing close-bracket with an error message.
then
  echo "No command-line arguments."
else
  echo "First command-line argument is $1."
fi

echo


if /usr/bin/[ -z "$1" ]       # Again, functionally identical to above.
# if /usr/bin/[ -z "$1"       # Works, but gives an error message.
#                             # Note:
#                               This has been fixed in Bash, version 3.x.
then
  echo "No command-line arguments."
else
  echo "First command-line argument is $1."
fi

echo

exit 0