shell循环示例

for循环示例

for循环语法：

				
								1
							
								for VARIABLE in 1 2 3 4 5 .. N
						
								2
							
								do
						
								3
							
								         command1
						
								4
							
								         command2
						
								5
							
								         commandN
						
								6
							
								done

				
								01
							
								#!/bin/bash
						
								02
							
								03
							
								for i in 1 2 3 4 5
						
								04
							
								05
							
								do
						
								06
							
								07
							
								echo "Welcome $i times"
						
								08
							
								09
							
								done
						
								10

bash version 3.0+版本

				
								#!/bin/bash
						
								 for i in {1..5}
						
								do
						
								   echo "Welcome $i times"
						
								done

bash version 4版本

				
								#!/bin/bash
						
								echo "Bash version ${BASH_VERSION}..."
						
								for i in {0..10..2}
						
								  do
						
								     echo "Welcome $i times"
						
								 done

含有“seq”命令的语法示例

				
								#!/bin/bash
						
								for i in $(seq 1 2 20)
						
								do
						
								   echo "Welcome $i times"
						
								done

for循环的三个表达式

语法如下：

				
								for (( EXP1; EXP2; EXP3 ))
						
								do
						
								         command1
						
								         command2
						
								         command3
						
								done

示例如下：

				
								#!/bin/bash
						
								for (( c=1; c<=5; c++ ))
						
								do
						
								         echo "Welcome $c times..."
						
								done

效果：

				
								Welcome 1 times
						
								Welcome 2 times
						
								Welcome 3 times
						
								Welcome 4 times
						
								Welcome 5 times

for的无限循环

				
								#!/bin/bash
						
								for (( ; ; ))
						
								do
						
								   echo "infinite loops [ hit CTRL+C to stop]"
						
								done

break条件语句

				
								for I in 1 2 3 4 5
						
								do
						
								  statements1      #Executed for all values of ''I'', up to a disaster-condition if any.
						
								  statements2
						
								  if (disaster-condition)
						
								  then
						
								         break                #Abandon the loop.
						
								  fi
						
								  statements3          #While good and, no disaster-condition.
						
								done

下面的shell脚本将通过在/ etc目录中存储的所有文件。 for循环将放弃当/ etc / resolv.conf的文件中找到。

				
								#!/bin/bash
						
								for file in /etc/*
						
								do
						
								         if [ "${file}" == "/etc/resolv.conf" ]
						
								         then
						
								                 countNameservers=$(grep -c nameserver /etc/resolv.conf)
						
								                 echo "Total  ${countNameservers} nameservers defined in ${file}"
						
								                 break
						
								         fi
						
								done

continue条件语句

				
								for I in 1 2 3 4 5
						
								do
						
								  statements1      #Executed for all values of ''I'', up to a disaster-condition if any.
						
								  statements2
						
								  if (condition)
						
								  then
						
								         continue   #Go to next iteration of I in the loop and skip statements3
						
								  fi
						
								  statements3
						
								done

利用这个脚本在命令行中指定的所有文件名的备份。如果。bak文件存在，它会跳过cp命令。

				
								#!/bin/bash
						
								FILES="$@"
						
								for f in $FILES
						
								do
						
								        # if .bak backup file exists, read next file
						
								         if [ -f ${f}.bak ]
						
								         then
						
								                 echo "Skiping $f file..."
						
								                 continue  # read next file and skip cp command
						
								         fi
						
								        # we are hear means no backup file exists, just use cp command to copy file
						
								         /bin/cp $f $f.bak
						
								done

(责任编辑：IT)

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