Bash:从包含完整路径的读取行中提取用户路径 (/home/userID) 并替换为 "~"

Question

我一次构建一个 bash 脚本文件。我像我一样学习去。但是此时我无法在网上找到任何可以帮助我的东西:我需要从大字符串中提取子字符串，我发现使用 ${}(花括号)的两种方法都行不通。

第一个，${x#y}，没有做它应该做的事情。

第二个，${x:p} 或 ${x:p:n}，不断报告错误替换。
它似乎只适用于常量。

${#x} 返回字符串长度作为文本，而不是数字，这意味着它不适用于 ${x:p} 或 ${x:p:n}.

事实是，让 bash 做很多数学运算似乎真的很难。除了 for 语句。但这只是在计算。这不是 for 循环的任务。

我在这里合并了我的脚本文件，以帮助大家理解我在做什么。它用于处理 PureBasic 源文件，但您只需更改 grep 的“--include=”参数，它就可以搜索其他类型的文本文件。

#!/bin/bash
home=$(echo ~)                              # Copy the user's path to a variable named home  
len=${#home}                                # Showing how to find the length.  Problem is, this is treated  
                                            # as a string, not a number.  Can't find a way to make over into  
                                            # into a number.  
echo $home "has length of" $len "characters."  
read -p "Find what: " what                  # Intended to search PureBasic (*.pb?) source files for text matches  
grep -rHn $what $home --include="*.pb*" --exclude-dir=".cache" --exclude-dir=".gvfs" > 1.tmp  
while read line                             # this checks for and reads the next line  
do                                          # the closing 'done' has the file to be read appended with "<"  
  a0=$line                                  # this is each line as read  
  a1=$(echo "$a0" | awk -F: '{print $1}')   # this gets the full path before the first ':'  
  echo $a0                                  # Shows full line  
  echo $a1                                  # Shows just full path  
  q1=${line#a1}  
  echo $q1                                  # FAILED!  No reported problem, but failed to extract $a1 from $line.  
  q1=${a0#a1}  
  echo $q1                                  # FAILED!  No reported problem, but failed to extract $a1 from $a0.  
  break                                     # Can't do a 'read -n 1', as it just reads 1 char from the next line.  
                                            # Can't do a pause, because it doesn't exist.  So just run from the  
                                            # terminal so that after break we can see what's on the screen  .
  len=${#a1}                                # Can get the length of $a1, but only as a string  
  # q1=${line:len}                          # Right command, wrong variable   
  # q1=${line:$len}                         # Right command, right variable, but wrong variable type  
  # q1=${line:14}                           # Constants work, but all $home's aren't 14 characters long  
done < 1.tmp  

Answer 1

以下作品:

x="/home/user/rest/of/path"
y="~${x#/home/user}"
echo $y

会输出

~/rest/of/path

如果你想在变量中使用“/home/user”，比如说前缀，你需要在#之后使用$，即${x#$prefix}，我认为是你的问题。