我使用stderr在循环内存储，并从循环外读取。 这里var i最初被设置并在循环中读取为1。

# reading lines of content from 2 files concatenated
# inside loop: write value of var i to stderr (before iteration)
# outside: read var i from stderr, has last iterative value

f=/tmp/file1
g=/tmp/file2
i=1
cat $f $g | \
while read -r s;
do
  echo $s > /dev/null;  # some work
  echo $i > 2
  let i++
done;
read -r i < 2
echo $i

或者使用heredoc方法来减少子shell中的代码量。 注意，迭代的i值可以在while循环之外读取。

i=1
while read -r s;
do
  echo $s > /dev/null
  let i++
done <<EOT
$(cat $f $g)
EOT
let i--
echo $i

嗯…我几乎发誓，这是为原来的伯恩壳工作，但没有访问到一个运行的副本，只是现在检查。

然而，对于这个问题，有一个非常琐碎的变通办法。

将脚本的第一行更改为:

#!/bin/bash

to

#!/bin/ksh

果不其然!如果您已经安装了Korn shell，那么在管道的末尾读取就可以了。

echo -e $lines | while read line 
    ...
done

while循环在子shell中执行。因此，一旦子shell退出，您对变量所做的任何更改都将不可用。

相反，你可以使用一个here字符串来重写while循环，使其位于主shell进程中;只有echo -e $lines将在子shell中运行:

while read line
do
    if [[ "$line" == "second line" ]]
    then
        foo=2
        echo "Variable \$foo updated to $foo inside if inside while loop"
    fi
    echo "Value of \$foo in while loop body: $foo"
done <<< "$(echo -e "$lines")"

在分配行时，可以通过立即展开反斜杠序列来消除上面here-string中相当难看的echo。美元的…的引用形式可以用在这里:

lines=$'first line\nsecond line\nthird line'
while read line; do
    ...
done <<< "$lines"

虽然这是一个老问题，并被问了几次，以下是我在摆弄这里的字符串后所做的事情，唯一适合我的选择是在while循环子shell期间将值存储在文件中，然后检索它。简单。

使用echo语句存储，使用cat语句检索。bash用户必须具有chown目录或读写chmod权限。

#write to file
echo "1" > foo.txt

while condition; do 
    if (condition); then
        #write again to file
        echo "2" > foo.txt      
    fi
done

#read from file
echo "Value of \$foo in while loop body: $(cat foo.txt)"

我使用stderr在循环内存储，并从循环外读取。 这里var i最初被设置并在循环中读取为1。

# reading lines of content from 2 files concatenated
# inside loop: write value of var i to stderr (before iteration)
# outside: read var i from stderr, has last iterative value

f=/tmp/file1
g=/tmp/file2
i=1
cat $f $g | \
while read -r s;
do
  echo $s > /dev/null;  # some work
  echo $i > 2
  let i++
done;
read -r i < 2
echo $i

或者使用heredoc方法来减少子shell中的代码量。 注意，迭代的i值可以在while循环之外读取。

i=1
while read -r s;
do
  echo $s > /dev/null
  let i++
done <<EOT
$(cat $f $g)
EOT
let i--
echo $i

用一个非常简单的方法怎么样

    +call your while loop in a function 
     - set your value inside (nonsense, but shows the example)
     - return your value inside 
    +capture your value outside
    +set outside
    +display outside


    #!/bin/bash
    # set -e
    # set -u
    # No idea why you need this, not using here

    foo=0
    bar="hello"

    if [[ "$bar" == "hello" ]]
    then
        foo=1
        echo "Setting  \$foo to $foo"
    fi

    echo "Variable \$foo after if statement: $foo"

    lines="first line\nsecond line\nthird line"

    function my_while_loop
    {

    echo -e $lines | while read line
    do
        if [[ "$line" == "second line" ]]
        then
        foo=2; return 2;
        echo "Variable \$foo updated to $foo inside if inside while loop"
        fi

        echo -e $lines | while read line
do
    if [[ "$line" == "second line" ]]
    then
    foo=2;          
    echo "Variable \$foo updated to $foo inside if inside while loop"
    return 2;
    fi

    # Code below won't be executed since we returned from function in 'if' statement
    # We aready reported the $foo var beint set to 2 anyway
    echo "Value of \$foo in while loop body: $foo"

done
}

    my_while_loop; foo="$?"

    echo "Variable \$foo after while loop: $foo"


    Output:
    Setting  $foo 1
    Variable $foo after if statement: 1
    Value of $foo in while loop body: 1
    Variable $foo after while loop: 2

    bash --version

    GNU bash, version 3.2.51(1)-release (x86_64-apple-darwin13)
    Copyright (C) 2007 Free Software Foundation, Inc.