Summary of various problems encountered from copying shell scripts from the Internet to running under linux

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1. Error reporting phenomenon: ': No such file or directory

Solution: Execute under linux system: dos2unix filename

The cause of the problem: the essence is that the binary symbol ^M in the file is garbled

Reference link: Four ways to drop ^M in Linux Develop Paper

2. Error reporting phenomenon: env: can't execute 'bash': No such file or directory

Workaround: Replace #!/bin/bash with #!/bin/sh

Cause of the problem: the essence is sh and bash problem

Starting from ubuntu 6.10, ubuntu has replaced the previous default bash shell with a dash shell , which shows that the /bin/sh link has reversed /bin/dash instead of the traditional /bin/bash .

It can be seen through the ls -l /bin/*sh command:

So it prompts that bash cannot be found. The solution is to use bash instead of sh to run the script: bash test.sh or replace #!/bin/bash with #!/bin/sh

3. Problems with garbled characters of various punctuation marks

1. Error reporting phenomenon: prompt xxx quot: not found

Solution: Replace " with "

The cause of the problem: the punctuation mark " is garbled, just replace " with "

2. && punctuation garbled characters: use && to replace garbled characters &&
3. >> garbled characters: use >> to replace garbled
characters & gt;> character >

Fourth, the error phenomenon: Syntax error: Bad for loop variable error solution

Reference link:

Syntax error: Bad for loop variable error solution

Syntax error: Bad for loop variable (Syntax error: Bad for loop variable)_Computer Training

Solution: Replace the for loop method with the while loop method

Cause of problem:for (( expr ; expr ; expr )) This C language format syntax isshnot available

It can be seen through the ls -l /bin/*sh command:

So when using the sh command to execute the script, dash is actually used, and dash does not support the for loop writing method in the C language format.

5. The meaning of eq, ne, le, ge, lt, gt in linux #!/bin/sh script

Reference link: https://www.cnblogs.com/hankyoon/p/12612549.html

if ［ 1 -ne 1 ］;then
...
fi

-eq: equal to
-ne: not equal to
-le: less than or equal to
-ge: greater than or equal to
-lt: less than
-gt: greater than

6. Error reporting phenomenon: syntax error: unexpected end of file (expecting "}")

Solution: Find the missing } symbol and add it

Cause of the problem: { } symbols do not appear in pairs