Tutorial

bash for循环

# basic construct
for arg in [list]
do
 command(s)...
done

对于每次通过循环,arg都会使用列表中每个连续值的值。然后执行命令。

# loop on array member
NAMES=(Joe Jenny Sara Tony)
for N in ${NAMES[@]} ; do
  echo "My name is $N"
done

# loop on command output results
for f in $( ls prog.sh /etc/localtime ) ; do
  echo "File is: $f"
done

bash while循环

# basic construct
while [ condition ]
do
 command(s)...
done

while构造会测试条件,如果为true,则执行命令。只要条件为真,它就会不断循环。

COUNT=4
while [ $COUNT -gt 0 ]; do
  echo "Value of count is: $COUNT"
  COUNT=$(($COUNT - 1))
done

bash直到循环

# basic construct
until [ condition ]
do
 command(s)...
done

直到构造测试条件,如果为false,则执行命令。只要条件为假,它就保持循环(与while构造相反)

COUNT=1
until [ $COUNT -gt 5 ]; do
  echo "Value of count is: $COUNT"
  COUNT=$(($COUNT + 1))
done

“break”和“continue”语句

break和continue可用于控制for,while和直到构造的循环执行。continue用于跳过特定循环迭代的其余部分,而break用于跳过整个循环的其余部分。一些例子:

# Prints out 0,1,2,3,4

COUNT=0
while [ $COUNT -ge 0 ]; do
  echo "Value of COUNT is: $COUNT"
  COUNT=$((COUNT+1))
  if [ $COUNT -ge 5 ] ; then
    break
  fi
done

# Prints out only odd numbers - 1,3,5,7,9
COUNT=0
while [ $COUNT -lt 10 ]; do
  COUNT=$((COUNT+1))
  # Check if COUNT is even
  if [ $(($COUNT % 2)) = 0 ] ; then
    continue
  fi
  echo $COUNT
done

Exercise

在本练习中,您将需要循环访问并按接收顺序从数字列表中打印出所有偶数。不要打印序列中237之后的任何数字。

Tutorial Code

#!/bin/bash
NUMBERS=(951 402 984 651 360 69 408 319 601 485 980 507 725 547 544 615 83 165 141 501 263 617 865 575 219 390 237 412 566 826 248 866 950 626 949 687 217 815 67 104 58 512 24 892 894 767 553 81 379 843 831 445 742 717 958 609 842 451 688 753 854 685 93 857 440 380 126 721 328 753 470 743 527)

# write your code here

Expected Output

402 984 360 408 980 544 390

Solution

#!/bin/bash
NUMBERS=(951 402 984 651 360 69 408 319 601 485 980 507 725 547 544 615 83 165 141 501 263 617 865 575 219 390 237 412 566 826 248 866 950 626 949 687 217 815 67 104 58 512 24 892 894 767 553 81 379 843 831 445 742 717 958 609 842 451 688 753 854 685 93 857 440 380 126 721 328 753 470 743 527)

# write your code here
for gg in ${NUMBERS[@]}; do
	
    if [ $gg == 237 ]; then
    	break;
    elif [ $(($gg % 2)) == 0 ]; then
    	echo $gg
    fi
done