Linux shell script if condition control flow methods All In One
if...then...fi / if...then...else..fi / if...then...elif...then...fi
#!/usr/bin/env bash
if bug
then
echo "bug ✅"
else
echo "bug ❌"
fi
if pwd
then
echo "pwd ✅"
else
echo "pwd ❌"
fi
<<EOF
./bug.sh:行3: bug：未找到命令
bug ❌
/home/eric/Desktop/if-condition-types
pwd ✅
EOF
condition types
ifcommandtestcondition (整数数值、字符串、文件)[ condition ]单方括号 (整数数值、字符串、文件)[[ condition ]]双方括号 (浮点数数值、字符串、文件)
# if command; then
if pwd; then
echo "print current path"
fi
# or
if pwd
then
echo "print current path"
fi
var1=3
var2=7
# test condition
if test $var1 -gt $var2; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
test等价于[]
var1=3
var2=7
# [ condition ], 单方括号 / single square brackets
#⚠️ 注意方括号的两边必须各有一个空格
if [ $var1 -gt $var2 ]; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
var1=3
var2=7
# [[ condition ]], 双方括号 / double square brackets
#⚠️ 注意方括号的两边必须各有一个空格
if [[ $var1 > $var2 ]]; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
demos
#!/usr/bin/env bash
if bug
then
echo "bug ✅"
else
echo "bug ❌"
fi
if pwd
then
echo "pwd ✅"
else
echo "pwd ❌"
fi
<<EOF
./bug.sh:行3: bug：未找到命令
bug ❌
/home/eric/Desktop/if-condition-types
pwd ✅
EOF
#!/usr/bin/env bash
var1=3
var2=7
# test condition
if test $var1 -gt $var2; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
<<EOF
3 little than 7
EOF
#!/usr/bin/env bash
var1=3
var2=7
# [ condition ], 单方括号 / single square brackets
#⚠️ 注意方括号的两边必须各有一个空格
if [ $var1 -gt $var2 ]; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
<<EOF
3 little than 7
EOF
#!/usr/bin/env bash
var1=3
var2=7
# [[ condition ]], 双方括号 / double square brackets
#⚠️ 注意方括号的两边必须各有一个空格
if [[ $var1 > $var2 ]]; then
echo "$var1 great than $var2"
else
echo "$var1 little than $var2"
fi
<<EOF
3 little than 7
EOF
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