To remove the last character from a string in Bash, you can use the sed command:
$ sed 's/.$//' <<< "Hello world!" Hello world
This will remove the last character (in this case, an exclamation mark) from the string.
If you want to remove the last character from each line in a file, you can use the sed command in combination with the tr command:
$ tr -d '\n' < input.txt | sed 's/.$//'
This will remove the last character from each line in the input.txt file, and print the resulting string to standard output.
To remove the last word from a line in Bash, you can use the awk command:
$ awk '{$NF=""; print}' <<< "Hello world!"
Hello
This will remove the last word (in this case, "world!") from the line, and print the resulting string to standard output. Note that this will also remove the space after the last word, so you may need to add it back if necessary.
Overall, there are many ways to remove the last character or word from a string in Bash, and the method you choose will depend on your specific needs and the context in which you are working.