linux shell脚本中for循环的语法
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syntax of for loop in linux shell scripting
提问by mkab
I have a problem implementing a for loop. I get this error when I execute my script
我在实现 for 循环时遇到问题。执行脚本时出现此错误
test1.sh: 2: Syntax error: Bad for loop variable
test1.sh: 2: 语法错误：循环变量错误
I don't understand this error.
我不明白这个错误。
This is my script
这是我的脚本
#!/bin/bash
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times..."
done
can any one tell me syntax for for loop in sh(in ubuntu it links to dash shell) shell in ubuntu?
谁能告诉我 ubuntu 中 sh（在 ubuntu 中它链接到 dash shell）shell 中 for 循环的语法？
采纳答案by Michael Krelin - hacker
You probably run it with sh, not bash. Try bash test1.sh, or ./test1.shif it's executable, but not sh test1.sh.
您可能使用sh，而不是 来运行它bash。尝试bash test1.sh，或者./test1.sh如果它是可执行的，但不是sh test1.sh。
回答by David W.
Your shell script (as shown) runs in both Korn shell and Bash. Some thoughts:
您的 shell 脚本（如图所示）在 Korn shell 和 Bash 中运行。一些想法：
- You might need a space after the shebang (#! /bin/bash and not #!/bin/bash). However, Dennis Ritchie had originally specified the space is optional. Besides, it isn't the error you get with Bourne shell (you get
syntax error: '(' unexpectedinstead). - Are you on a Windows system? Just a stab in the dark. This doesn't look like a Windows error.
- Is this Solaris or HP/UX system? They might not be running true versions of Bash, or maybe an older version. However, even the oldest version of Bash recognizes the
for ((x;y;z))construct.
- 您可能需要在 shebang 之后留一个空格（#!/bin/bash 而不是 #!/bin/bash）。然而，丹尼斯·里奇最初指定的空格是可选的。此外，这不是您使用 Bourne shell 遇到的错误（您会得到
syntax error: '(' unexpected）。 - 你在Windows系统上吗？只是在黑暗中刺伤。这看起来不像是 Windows 错误。
- 这是 Solaris 还是 HP/UX 系统？他们可能没有运行真正的 Bash 版本，或者可能是旧版本。然而，即使是最旧版本的 Bash 也能识别该
for ((x;y;z))构造。
Try this:
尝试这个：
#! /bin/bash
set -vx
echo "Random = $RANDOM" #Test for bash/Kornshell. Will be blank in other shells
echo $BASH_VERSINFO[0] = ${BASH_VERSINFO[0]} #Should only work in BASH
echo $BASH_VERSINFO[1] = ${BASH_VERSINFO[1]}
echo $BASH_VERSINFO[2] = ${BASH_VERSINFO[2]}
echo $BASH_VERSINFO[3] = ${BASH_VERSINFO[3]}
echo $BASH_VERSINFO[4] = ${BASH_VERSINFO[4]}
echo $BASH_VERSINFO[5] = ${BASH_VERSINFO[5]}
for ((c=0, c<=5, c++))
do
echo "Welcome $c times"
done
- The
set -xvwill display all lines as they are executed. - The
$RANDOMshould display a value if this is either BASH or Kornshell (your for loop will work in either one). - The
{$BASH_VERINFO[x]}should only be set if this is truly BASH. These aren't even set even if you run Korn shell after you're in BASH (unlike $SHELL which will still containbash).
- 在
set -xv执行时为它们会显示所有行。 - 的
$RANDOM，如果这是无论是bash或Kornshell（您的循环将在任何一个工作）应显示的值。 - 的
{$BASH_VERINFO[x]}，如果这是真正的BASH只应设置。即使您在 BASH 中运行 Korn shell（与仍包含 的 $SHELL 不同），这些甚至都不会设置bash。
If the for loop still gives you trouble, just delete it. Somewhere in this script, we'll find out if you're really executing a bash shell or not.
如果 for 循环仍然给您带来麻烦，只需将其删除即可。在这个脚本的某个地方，我们会发现你是否真的在执行一个 bash shell。
回答by Ken Bloom
A standard POSIX shell only accepts the syntax for varname in list
标准的 POSIX shell 只接受语法 for varname in list
The C-like for-loop syntax for (( expr1; expr2; expr3 ))is a bashism.
类似 C 的 for 循环语法for (( expr1; expr2; expr3 ))是一种 bashism。
You can get similar behavior in the standard POSIX shell using for c in $(seq 1 5)
您可以使用以下命令在标准 POSIX shell 中获得类似的行为 for c in $(seq 1 5)
回答by Ankur Agarwal
What does
有什么作用
ls -l /bin/sh
give on your machine ?
给你的机器？
Make sha symbolic link to bashand then you can do sh ./test1.sh
建立sh一个符号链接bash，然后你可以做sh ./test1.sh
