您正在执行命令替换set。在命令替换块内设置的变量在展开后被丢弃。您需要的是命令替代grep top def.tcl | tail -1 | item 2：

alias unit "set unit = "\""`grep top def.tcl | tail -1 | item 2`"\"""
alias ipcd 'unit ; cd flow/$unit/ip/'

如果你想让它成为一个函数，请在.cshrc或.tcshrc中设置以下内容：

alias function 'set argv = ( \!* ) ; source ~/.cshfuncs'

然后将函数添加到.cshfuncs：

# Functions for C Shell.

set ret = -1
onintr exit

switch ("$1")
  case "ipcd":
    set unit = "`grep top def.tcl | tail -1 | item 2`"
    cd "flow/$unit/ip/"
    set ret = 0
    breaksw
  case "myfunc":
    echo "A function."
    set ret = 0
    breaksw
  default:
    echo "Function $1 not set."
endsw

exit:
set argv
exit $ret