#!/bin/sh

str="/path/to/foo.txt"

# 使用if语句
if echo "$str" | grep -q -E '\\.txt$'
then
	echo "true"
else
	echo "false"
fi

# 写成一行
echo "$str" | grep -q -E '\\.txt$' && echo true || echo false
grep -q -E '\\.txt$' <<< "$str" && echo true || echo false

#!/bin/sh

str="/path/to/foo.txt"

# 使用if语句
if expr "$str" : '.\*\\.txt$' &>/dev/null
then
	echo "true"
else
	echo "false"
fi

# 写成一行
expr "$str" : '.\*\\.txt$' &>/dev/null && echo true || echo false

### \# 方法三、使用case指令

#!/bin/sh

str="/path/to/foo.txt"

case "$str" in
	\*.txt ) echo "true";;
	\* ) echo "false";;
esac

#!/bin/bash

# BASH中的正则表达式
\[\[ "/path/to/foo.txt" =~ .\*txt$ \]\] && echo "true" || echo "false"

# BASH的特殊语法
\[\[ "/path/to/foo.txt" = \*txt \]\] && echo "true" || echo "false"

for line in \`cat filename\`
do
 echo $line
done

for line in $(cat filename)
do
 echo $line
done

while read -r line
do
 echo $line
done < filename

if [ -z $var ];then
	echo "not defined";
else
	echo "defined";
fi