I know that I can redirect the standard error output stream by: $ ./my-C-binary 2>error.log

What if I want to ignore the first two characters of anything from stderr before writing to the file? I've searched but I can't seem to find a way to do so. I'm not allowed to re-build my-C-binary (i.e. not allowed to change the source code). I am also not allowed to write an additional program to help with the task, it must be solved with a single command line to modify the 2>error.log portion. I don't know how to do that even after a few days of searching and trying.

Let's say the output of stderr is:

The quick brown fox jumps over the lazy dog.

The text in error.log must be:

e quick brown fox jumps over the lazy dog.

Thanks in advance for any suggestions and help.

CodePudding user response：

You can pipe the output through the tail command to ask it to skip the first two bytes:

$ ./my-C-binary |& tail -c  2 >error.log

Unfortunately this will pipe both standard error and standard output. To only get standard error, you need to do it in two steps:

1. Run the program like you do now, redirecting standard error to its file
2. Modify the file to "remove" the two first characters

CodePudding user response：

Combining this answer using process substitution to redirect stderr in bash with @Someprogrammerdude's use of tail:

./my-C-binary 2> >(tail -c 3 > error.log)

As an aside, note the " 3" parameter to tail: The number indicates the 1-based index of the character where output starts; if you want to skip the first two characters, you start with the third.

CodePudding user response：

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