bash:bash脚本给出了错误的替换错误_Bash

bash:bash脚本给出了错误的替换错误

bash

bash:bash脚本给出了错误的替换错误,bash,Bash,脚本： #/bin/bash url=${cat/var/scripts/test.txt | grep-oP'（？正确的语法是： ./script.sh: line 3: ${cat /var/scripts/test.txt | grep -oP '(?<=display_url":")[^"]+'}: bad substitution ${VARIABLE}用于变量扩展，$（command）用于命令替换 ./script.sh: line 3: ${cat /var/scripts

脚本：

#/bin/bash
url=${cat/var/scripts/test.txt | grep-oP'（？正确的语法是：
./script.sh: line 3: ${cat /var/scripts/test.txt | grep -oP '(?<=display_url":")[^"]+'}: bad substitution

${VARIABLE}
用于变量扩展，$（command）
用于命令替换
./script.sh: line 3: ${cat /var/scripts/test.txt | grep -oP '(?<=display_url":")[^"]+'}: bad substitution

url=$(cat /var/scripts/test.txt | grep -oP '(?<=display_url":")[^"]+')

url=$(grep -oP '(?<=display_url":")[^"]+' /var/scripts/test.txt)

          $(command)
   or
          `command`