test 命令

[root@localhost shell]# type test
test is a shell builtin
[root@localhost shell]# type [
[ is a shell builtin
[root@localhost shell]# type [[
[[ is a shell keyword
[root@localhost shell]# type let
let is a shell builtin

#!/bin/bash
if cmp a.txt b.txt &> /dev/null
then
    echo 'Files a and b are identical.'
else
    echo 'Files a and b are diff.'
fi

if [ condition-true ]
then
   command 1
   command 2
   ...
else  # Or elif ...
      # Adds default code block executing if original condition tests false.
   command 3
   command 4
   ...
Fi

if [ condition1 ]
then
   command1
   command2
   command3
elif [ condition2 ]
# Same as else if
then
   command4
   command5
else
   default-command
fi
 

 

#!/bin/bash
var1=7
var2=10

if (( var1 > var2 )) # not $var1 $var2, but is ok.
then
    echo "var1 is greater than var2"
else
    echo "var1 is less than var2"
fi
exit 0

#!/bin/bash

num1=6
num2=9
if [ $num1 -ne $num2 ]
then
    echo "$num1 is not equal to $num2"
fi

#!/bin/bash

device1="/dev/sda1"
if [ -b "$device1" ]
then
    echo "$device1 is a block device."
fi

device2='/dev/tty0'
if [ -c "$device2" ]
then
    echo "$device2 is a character device."
fi