[英]How to use global arrays in bash?
我在SO和google中搜索了2天的解决方案,但是我没有运气。 我的问题是我有一个数组,并用0初始化了它的元素,并且在for \\ while循环范围内修改了它的元素值。 但是当我在循环外打印数组的值时,我发现所有的0都是它们的初始值!
这是我的代码:
#!/bin/bash
#
# This is a script to reformat CSV files into pretty-formatted txt files.
clear
echo 'This is a script to reformat CSV files into pretty-formatted txt files.'
echo
# Get number of elements.
elements=$(cat CSV_File | sed -n 1'p' | tr ',' '\n' | wc -l)
# "cat CSV_File" for getting text of the file.
# "sed -n 1'p'" for getting only first line.
# "tr ',' '\n'" for replacing ',' with '\n'.
# "wc -l" for getting number of lines (i.e number of elements).
# Get number of lines.
lines=$(cat CSV_File | wc -l)
# "cat CSV_File" for getting text of the file.
# "wc -l" for getting number of lines.
# Initiate an array for elements' lengths.
for ((i=1; $i < (( $elements + 1 )) ;i++))
do lengths[$i]="0"
done
# Find tallest element of each column and put the values into 'lengths' array.
for ((i=1; $i <= $lines ;i++))
do
j="1"
cat CSV_File | sed -n ${i}'p' | tr ',' '\n' | while read element
do
if [ ${lengths[$j]} -le ${#element} ]
then lengths[$j]=${#element}
fi
(( j++ ))
done
done
echo ${lengths[1]} # It should print 5 not 0
echo ${lengths[2]} # It should print 4 not 0
echo ${lengths[3]} # It should print 19 not 0
echo ${lengths[4]} # It should print 11 not 0
echo ${lengths[5]} # It should print 2 not 0
echo ${lengths[6]} # It should print 5 not 0
echo ${lengths[7]} # It should print 14 not 0
echo
...
这是CSV_File的内容:
Jones,Bill,235 S. Williams St.,Denver,CO,80221,(303) 244-7989
Smith,Tom,404 Polk Ave.,Los Angeles,CA,90003,(213) 879-5612
请注意,当我将echo
放入if语句中时,它将输出正确的值:
if [ ${lengths[$j]} -le ${#element} ]
then lengths[$j]=${#element}
echo ${lengths[$j]}
fi
我在做什么错? 我想念什么吗?
| while read element; do ... done
| while read element; do ... done
| while read element; do ... done
在子外壳| while read element; do ... done
中运行,因此在子外壳程序退出时,其对全局的更新会丢失。
一种解决方案是使用bash的“进程替换”来获取while循环的输入,以使其在子shell中运行。 请参阅: 在bash中读取多行而不产生新的subshell?
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