在脚本运行时编辑脚本会发生什么？

Question

如果我是脚本文件并在它仍在运行时保存它会发生什么,并且它会打印我需要的结果.

Answer 1

我们来试试吧.

创建一个脚本test.sh:

#!/usr/bin/env bash

sleep 1
echo 'echo "executed overwritten"' >> "$0"   # append to self
sleep 1
echo 'executed original'

并执行它:

$ bash --version
GNU bash, version 4.2.24(1)-release (i686-pc-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ chmod +x test.sh 
$ ./test.sh 
executed original
executed overwritten
$ 

请注意,bash继续阅读修改后的文件.它在文件更改时保持其在文件中的当前位置(以字节为单位).

作为演示,脚本

#!/usr/bin/env bash

sleep 1
dd if=/dev/urandom bs=1024 count=1 of="$0" &>/dev/null   # overwrite self
sleep 1
echo 'executed original'

给出输出

$ ./test.sh 
./test.sh: line 6: syntax error near unexpected token `$'\311\262\203''
./test.sh: line 6: `??z?e?9)?v???y?a??44'{?d??4\:?A????????&?$?????l?
@(???4??O?I?n>??7??P?M?a??X.?S?a???V?m?~O<??{}??????J??$??TOtRd??Nw?&??B?Dz????-??<`?P<?N???rT?Jq?L????JY?*hz???M?????i????S+?????\??c???m?NKV?8|??xvX}??V????PTd??9??7???|??/??X??
                                                                                                       ??0¤k??_?R???e?*???(qu:UU?p/j??n??b?_?UR?3????%Rn?|DE$8?QbaK)A?{ ??O>9??A?????lt?????g)s??O??M??@???w??|?????N??,W'

请注意,它试图执行随机乱码.

(这是Ubuntu 12.04.行为可能因其他shell而异.)