From 18d9845e52864dab6b28a9dae5843015adb0734b Mon Sep 17 00:00:00 2001
From: iProbe <iprobe@noreply.localhost>
Date: Sat, 12 Aug 2023 16:13:30 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20'shell/shell=E5=8F=98?=
 =?UTF-8?q?=E9=87=8F=E6=8F=90=E5=8F=96=E8=B5=8B=E5=80=BC.md'?=
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---
 shell/shell变量提取赋值.md | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 shell/shell变量提取赋值.md

diff --git a/shell/shell变量提取赋值.md b/shell/shell变量提取赋值.md
new file mode 100644
index 0000000..18c3e60
--- /dev/null
+++ b/shell/shell变量提取赋值.md
@@ -0,0 +1,7 @@
+|--|--|
+|表达式|含义|
+|${var:-aa}|若var为空或未设定, 返回aa, var值不变|
+|${var:=aa}|若var为空或未设定, 返回aa, var=aa|
+|${var:+aa}|若var有值 返回aa, var值不变|
+|${var:?aa}|若var为空或未设定 返回aa并退出shell, 若aa无值, 则输出parameter null or not set, 用于检测var是否被正确赋值|
+|-|-|
\ No newline at end of file