适用于Bash编程初学者小例子 - 第一篇 - 中道学友

适用于Bash编程初学者小例子 - 第一篇

如何声明字符串变量，并赋值？

#!/bin/bash
TARGET_CLUSTER_NODE_IP="10.245.110.69"
printf “%s \n” $TARGET_CLUSTER_NODE_IP

如何初始化一个字符串数组变量，并遍历输出其每一个字符串元素的值？

#!/bin/bash

declare -a string_array=("Hello world!" "How are you?" "Nice to meet you!" "How do you do?" )

# Read the array values with space
for str in "${string_array[@]}"; do
echo $str
done

如何SSH到另一台主机并在其上运行几个命令？

#!/bin/bash

# 先配置SSH的免密，之后执行此脚本

hostname
ssh root@10.245.110.69 'hostname; whoami; date'
hostname

如何使用IF语句比较字符串的值？

#!/bin/bash

string1="Hello World!"
string2="Hello Bash!"

if [[ $string1 == "Hello World!" ]]
then
     printf "Same! \n"
else
     print "Different! \n"
fi

if [[ $string2 = *"Bash"* ]]
then
     printf "Contains word 'Bash'. \n"
else
     printf "Does not contain the word. \n"
fi

如何把for语句放在一行里执行？

#!/bin/bash

# For statement in multiple lines
for((i=1;i<10;i+=2))
do
echo "Welcome $i times"
done

# For statement in one line
for((i=1;i<=10;i+=2)); do echo "Welcome $i times"; done

如何建立一个字符串数组，并且查看每一个字符串？

#!/bin/bash

declare -a flush_results

flush_results+=("1.Hello")
flush_results+=("2.World")
flush_results+=("3.Bash")

echo ${flush_results[0]}
echo ${flush_results[1]}
echo ${flush_results[2]}

echo ${flush_results[@]}

如何捕获一个命令的输出，并把输出存到一个变量里？

#!/bin/bash

declare OUTPUT=$(ssh root@10.111.111.111 isi_for_array isi_flush --dedupe-queue --dedupe-index )
# Output of command "#ssh root@10.111.111.111 isi_for_array isi_flush --dedupe-queue --dedupe-index":
#f810-4: Cache flushing complete.
#f810-3: Cache flushing complete.
#f810-2: Cache flushing complete.
#f810-1: Cache flushing complete.

#Show result in multi-lines
echo "$OUTPUT"

#Show result in one line
echo $OUTPUT

*为什么OUTPUT带不带双引号，区别这么大呢？

Jonathan Leffler解释如下：

The difference is that:
(1) the double-quoted version of the variable (echo "$VARIABLE") preserves internal spacing of the value exactly as it is represented in the variable — newlines, tabs, multiple blanks and all — whereas (2) the unquoted version (echo $VARIABLE) replaces each sequence of one or more blanks, tabs and newlines with a single space.
Thus:
(1) preserves the shape of the input variable, whereas
(2) creates a potentially very long single line of output”

如何把用换行符“\n”分隔的一个大字符串，分割开，并存放到一个数组中？

#!/bin/bash
declare OUTPUT=$(ssh root@10.111.111.111 isi_for_array isi_flush --dedupe-queue --dedupe-index )

echo "$OUTPUT"
echo $OUTPUT

SAVEIFS=$IFS    # Save current IFS
IFS=$'\n'       # Change IFS to new line
names=($OUTPUT) # split to array $names
IFS=$SAVEIFS    # Restore IFS

for ((j=0;j<4;j+=1)); do
     printf "Current is line: $j. \n"
     printf "%s \n" "${names[$j]}"
done