今天在处理文件时遇到个问题，当文件名包含空格时，for循环就出问题了。
例如，我在当前文件夹下建立3个文件名包含空格的文件：
代码如下:
keakons-MacBook-Pro:test keakon$ touch "test 1"
keakons-MacBook-Pro:test keakon$ touch "test 2"
keakons-MacBook-Pro:test keakon$ touch "test 3"
keakons-MacBook-Pro:test keakon$ ls
test 1 test 2 test 3
keakons-MacBook-Pro:test keakon$ touch "test 2"
keakons-MacBook-Pro:test keakon$ touch "test 3"
keakons-MacBook-Pro:test keakon$ ls
test 1 test 2 test 3
然后for循环输出文件名：
代码如下:
keakons-MacBook-Pro:test keakon$ for file in `ls`;
> do echo $file;
> done
test
1
test
2
test
3
> do echo $file;
> done
test
1
test
2
test
3
可以看到，文件名被分开了。
复制操作也不行：
代码如下:
keakons-MacBook-Pro:test keakon$ mkdir ../bak
keakons-MacBook-Pro:test keakon$ for file in `ls`; do cp "$file" ../bak; done
cp: bak is a directory (not copied).
cp: test: No such file or directory
cp: 1: No such file or directory
cp: test: No such file or directory
cp: 2: No such file or directory
cp: test: No such file or directory
cp: 3: No such file or directory
keakons-MacBook-Pro:test keakon$ for file in `ls`; do cp "$file" ../bak; done
cp: bak is a directory (not copied).
cp: test: No such file or directory
cp: 1: No such file or directory
cp: test: No such file or directory
cp: 2: No such file or directory
cp: test: No such file or directory
cp: 3: No such file or directory
要解决这个问题，当然就要从单词分隔符着手。而bash中使用的是$IFS（Internal Field Separator）这个变量，内容为" nt"：
代码如下:
keakons-MacBook-Pro:test keakon$ echo $IFS
keakons-MacBook-Pro:test keakon$ echo "$IFS" | od -t x1
0000000 20 09 0a 0a
0000004
keakons-MacBook-Pro:test keakon$ echo "" | od -t x1
0000000 0a
0000001
然后把它改成"nb"，记得修改前先保存一下：
代码如下:
keakons-MacBook-Pro:test keakon$ SAVEIFS=$IFS
keakons-MacBook-Pro:test keakon$ IFS=$(echo -en "nb")
keakons-MacBook-Pro:test keakon$ IFS=$(echo -en "nb")
现在再执行上述命令就正常了：
代码如下:
keakons-MacBook-Pro:test keakon$ for file in `ls`; do echo $file; done
test 1
test 2
test 3
keakons-MacBook-Pro:test keakon$ for file in `ls`; do cp "$file" ../bak; done
keakons-MacBook-Pro:test keakon$ ls ../bak
test 1 test 2 test 3
test 1
test 2
test 3
keakons-MacBook-Pro:test keakon$ for file in `ls`; do cp "$file" ../bak; done
keakons-MacBook-Pro:test keakon$ ls ../bak
test 1 test 2 test 3
最后，别忘了恢复$IFS：
代码如下:
keakons-MacBook-Pro:test keakon$ IFS=$SAVEIFS
keakons-MacBook-Pro:test keakon$ echo "$IFS" | od -t x1
0000000 20 09 0a 0a
0000004
keakons-MacBook-Pro:test keakon$ IFS=$(echo -en " nt")
keakons-MacBook-Pro:test keakon$ echo "$IFS" | od -t x1
0000000 20 0a 09 0a
0000004
keakons-MacBook-Pro:test keakon$ echo "$IFS" | od -t x1
0000000 20 09 0a 0a
0000004
keakons-MacBook-Pro:test keakon$ IFS=$(echo -en " nt")
keakons-MacBook-Pro:test keakon$ echo "$IFS" | od -t x1
0000000 20 0a 09 0a
0000004