shell基础学习中的字符串操作、for循环语句示例

#!/bin/bash
my_name="jxq"

echo $my_name
echo ${my_name}

# ------------------------------------
# 字符串操作
# ------------------------------------

# 单引号字符串的限制，双引号没有这些限制：
# 单引号里的任何字符都会原样输出，单引号字符串中的变量是无效的
# 单引号字串中不能出现单引号（对单引号使用转义符后也不行）
name="will"
age=24
my_full_name='${name}${age}'
echo ${my_full_name}
my_full_name="${name}${age}"
echo ${my_full_name}

# 字符串拼接
echo ${name}${age}

# 字符串长度
echo ${#name} # 4

# substring
message="i want to be healthy"
echo ${message:2} # want to be health, 2是position
echo ${message:2:4} # want，2是position，4是len

# delete shortest match from front: ${string#substring}
echo ${message#*want}
# delete shortest match from back: ${string%substring}
echo ${message%healthy}

# delete longest match from front: ${string##substring}
echo ${message##*h}
# delete longest match from back: ${string%%substring}
echo ${message%%t*}

# find and replace: ${string/pattern/replacement}
book_name="catch eye eye"
echo ${book_name/eye/cat}
# find and replace all match: ${string//pattern/replacement}
echo ${book_name//eye/cat}

file_path="/usr/local/bin"
# only replace when pattern match the beginning: ${string/#pattern/replacement}
echo ${file_path/#\/usr/tmp}
# only replace when pattern match the end: ${string/%pattern/replacement}
echo ${file_path/%bin/tmp}

# string index
stringz=abcabc123abcabc
echo `expr index "$stringz" c12` # mac osx不支持expr

# ------------------------------------
# 语句
# ------------------------------------

# if
if true
then
 echo "ok, true"
fi

# 写成一行
if true; then echo "ok"; fi

var='12'
if [ $var -eq 12 ]; then
    echo "this is a numeric comparison if example"
fi

if [ "$var" = "12" ]; then
    echo "this is a string if comparison example"
fi

if [[ "$var" = *12* ]]; then
    echo "this is a string regular expression if comparison example"
fi

name="jxq"
if [ "$name" = "jxq" ]; then
 echo "hello" $name
fi

# 循环语句
for item in `ls *.sh`
do
 echo $item
 echo "completed"
done

# 写成一行
for item in `ls *.sh`; do echo $item; echo "completed"; done;

counter=1
while :
do
 echo "bee"
 let "counter=$counter+1"
 if [ $counter -eq 3 ]; then
  break # break/continue与java类似
 fi
done

# case语句
opt="install"
case "${opt}" in
 "install" )
  echo "install..."
  exit

 
 "update" )
  echo "update..."
  exit

 
 *) echo "bad opt"
esac