我正在写一个脚本，当用户login时会被调用，并检查某个文件夹是否存在，或者是一个破碎的符号链接。 （这是在Mac OS X系统上，但问题纯粹是bash）。
这不是优雅的，它不工作，但现在看起来像这样：
#!/bin/bash # Often users have a messed up cache folder -- one that was redirected # but now is just a broken symlink. This script checks to see if # the cache folder is all right, and if not, deletes it # so that the system can recreate it. USERNAME=$3 if [ "$USERNAME" == "" ] ; then echo "This script must be run at login!" >&2 exit 1 fi DIR="~$USERNAME/Library/Caches" cd $DIR || rm $DIR && echo "Removed misdirected Cache folder" && exit 0 echo "Cache folder was fine." 问题的关键在于代字符扩展不能按我的意愿工作。
让我们说，我有一个名为george的用户，他的home文件夹是/a/path/to/georges_home 。 如果在一个shell中，我input：
cd ~george
它把我带到适当的目录。 如果我input：
HOME_DIR=~george echo $HOME_DIR
它给了我：
/a/path/to/georges_home
但是，如果我尝试使用一个variables，它不起作用：
USERNAME="george" cd ~$USERNAME -bash: cd: ~george: No such file or directory
我试过使用引号和反引号，但不知道如何使其正确扩展。 我该如何做这项工作？
附录
我只是想发布我的完整的脚本（实际上，它不像上面的工作那样丑陋！）并且说它似乎是正确的。
#!/bin/bash # Often users have a messed up cache folder -- one that was redirected # but now is just a broken symlink. This script checks to see if # the cache folder is all right, and if not, deletes it # so that the system can recreate it. #set -x # turn on to help debug USERNAME=$3 # Casper passes the user name as parameter 3 if [ "$USERNAME" == "" ] ; then echo "This script must be run at login!" >&2 exit 1 # bail out, indicating failure fi CACHEDIR=`echo $(eval echo ~$USERNAME/Library/Caches)` # Show what we've got ls -ldF "$CACHEDIR" if [ -d "$CACHEDIR" ] ; then # The cache folder either exists or is a working symlink # It doesn't really matter, but might as well output a message stating which if [ -L "$CACHEDIR" ] ; then echo "Working symlink found at $CACHEDIR was not removed." else echo "Normal directory found at $CACHEDIR was left untouched." fi else # We almost certainly have a broken symlink instead of the directory if [ -L "$CACHEDIR" ] ; then echo "Removing broken symlink at $CACHEDIR." rm "$CACHEDIR" else echo "Abnormality found at $CACHEDIR. Trying to remove." >&2 rm -rf "$CACHEDIR" exit 2 # mark this as a bad attempt to fix things; it isn't clear if the fix worked fi fi # exit, indicating that the script ran successfully, # and that the Cache folder is (almost certainly) now in a good state exit 0
使用$(eval echo ...) ：
michael:~> USERNAME=michael michael:~> echo ~michael /home/michael michael:~> echo ~$USERNAME ~michael michael:~> echo $(eval echo ~$USERNAME) /home/michael
所以你的代码应该是这样的：
HOMEDIR="$(eval echo ~$USERNAME)"
这是因为它将设置为variables时将〜george放在单引号内。 set -x对debugging很有用。
设置DIR时删除引号，当设置variables时，shell会扩展，这会给你想要的性能。
lrwxrwxrwx 1 root root 4 Sep 10 2004 /bin/sh -> bash* wmoore@bitbucket(/tmp)$ cat test.sh #!/bin/bash set -x cd ~root DIR=~root cd $DIR DIR="~root" cd $DIR wmoore@bitbucket(/tmp)$ sh test.sh + cd /root test.sh: line 4: cd: /root: Permission denied + DIR=/root + cd /root test.sh: line 8: cd: /root: Permission denied + DIR=~root + cd '~root' test.sh: line 12: cd: ~root: No such file or directory
Bash内置了导出的用户名和用户主目录的variables。 例如，如果用户在从~/.bash_profilelogin时调用脚本，则不需要将值作为parameter passing给脚本。
您可以使用$USER和$HOME因为它们已经在脚本环境中设置并可用，因为它们被标记为已导出。 我认为代字符扩展比在脚本中使用的东西更像是命令行方便。
DIR="$HOME/Library/Caches" cd "$DIR" || rm "$DIR" && echo "Removed misdirected Cache folder" && exit 1
以下列方式之一获取用户的主目录可能更加可靠：
getent passwd $USER | awk -F: '{print $(NF - 1)}'
要么
awk -F: -v user=$USER 'user == $1 {print $(NF - 1)}' /etc/passwd
另外， exit 0表示成功。 某种程度上，你的程序在删除目录时是成功的，但是它需要删除的事实是一个错误。 在任何情况下，如果此时exit 0 ，那么当脚本在最后的echo后退出时，您将无法区分差异，因为退出代码很可能为零。
从path$HOME/Library/Caches判断，这是Mac OS X，所以dscl是你的朋友。
如上所述， bash为你做，但如果它是一个Mac，你可以保证bash将可用（所以你不必担心严格符合/bin/sh无法应付它）。