将打印头集成到单行 bash CLI

Question

I have this command

$ sha1sum file.bin | cut -f1 -d " "

that computes the sha1sum of some eeprom content. The pipe followed by cut is to get rid of the file location in the output and retrieve only the sha1.

My issue is that I need to compute the sha1 over the first N lines of the file.bin . The file is a table/array of lines of 32 bytes (fixed lengths).

I know I have to put in some head -n N , but don't know how with the redirections. The syntax is head -n N <file> .

I tried naively sha1sum file.bin | cut -f1 -d " " | head -n 8 sha1sum file.bin | cut -f1 -d " " | head -n 8 sha1sum file.bin | cut -f1 -d " " | head -n 8 but it doesn't work. I need the shell to understand somehow this: sha1sum(head -n 8 file.bin) | cut -f1 -d " " sha1sum(head -n 8 file.bin) | cut -f1 -d " " , but we can't use mathematical function syntax in shell I guess...

How to do it please? Regards

Answer 1

Make the output of head the input of sha1sum , just as the output of sha1sum is the input to cut .

head -n 8 file.bin | sha1sum | cut -d " " -f1

or, if the file is binary, use the first N bytes with -c

head -c 1024 file.bin | sha1sum | cut -d " " -f1