判断量文件相等，判断某文本中是否含有某字符串

判断两个文件内容是否相等，cmp也可以换成是diff
if cmp a b &> /dev/null # 阻止输出.
then echo "Files a and b are identical."
else echo "Files a and b differ."
fi

判断某个文本中是否含有某字符串的例子：if-grep 结构

# 非常有用的"if-grep" 结构:

if grep -q Bash file
then echo "File contains at least one occurrence of Bash."
fi
word=Linux
letter_sequence=inu
if echo "$word" | grep -q "$letter_sequence"
# "-q"选项是用来阻止输出
then
echo "$letter_sequence found in $word"
else
echo "$letter_sequence not found in $word"
fi
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