shell bash

shell
  • the shell assigns its exit code to the $? environment variable. The $? variable is how we usually test whether a script has succeeded or not in its execution.

syntax

set -x

​ 1. Debugging: When you’re trying to troubleshoot a script, set -x helps you see exactly what commands are being executed and in what order.

​ 2. Selective Debugging: You can use set -x and set +x around specific parts of your script to narrow down the problematic sections.

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#!/bin/bash

echo "This is a normal message"

set -x  # Start debugging from this point
name="John"
echo "Hello, $name"

set +x  # Stop debugging after this point
echo "Debugging mode is now off"

output:

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This is a normal message
+ name=John
+ echo 'Hello, John'
Hello, John
Debugging mode is now off

shift 2

  • Removes the first two positional parameters from command line arguments
  • Shifts remaining parameters left by 2 positions
  • Useful when processing command line options/arguments in loops

point

  • (cd third-party && ...) 这样的语法，这是一个命令替换，它实质上是先临时改变到 third-party 目录执行里面的命令，然后脚本会继续在原先的目录中执行。