'git log -<number> --pretty="format:%H"' output does NOT append newline when piped into 'cat -e'

Question

I'm creating a shell script that displays the commit IDs of the 5 last git commits of my git repository.

Name of the script file: 'git_commit.sh' By "commit ID", I mean the full 40-character hexadecimal string. By git repository, I mean the current branch.

The output I expect:

yossi@hostname$ bash git_commit.sh | cat -e
42dfd4bdba4646b28136c4b0d71f76ae352aac10$
63a7f8e9e7f5ab2f29c4227440d78fc731201b89$
57361b98c8cb9041759461093ed38b7b8930e12e$
a05251da02f6c677f38f3ab68c95b2dd8812a822$
d17402aa3e3835e1b9e444482cda233e97e032d6$
yossi@hostname$

The command that was inserted in 'git_commit.sh':

git log -5 --pretty="format:%H"

And here's the output I get when I run the script:

yossi@hostname$ bash git_commit.sh | cat -e
42dfd4bdba4646b28136c4b0d71f76ae352aac10$
63a7f8e9e7f5ab2f29c4227440d78fc731201b89$
57361b98c8cb9041759461093ed38b7b8930e12e$
a05251da02f6c677f38f3ab68c95b2dd8812a822$
d17402aa3e3835e1b9e444482cda233e97e032d6yossi@hostname$

PROBLEM

• The 5th and last commit ID is not followed by a trailing $.
• There's no line break before the next command prompt.

Which means that there was no newline after the 5th and last commit ID when it was piped into the 'cat -e' command.

I thoroughly reviewed the manual page of 'git log' and wasn't able to find anything that explains that behavior.

ALTERNATIVES THAT I TESTED I tested the replacement of git log -5 --pretty="format:%H" by the following three commands:

• git log -5 --format="%H" | cat -e
• git log -5 --pretty="tformat:%H" | cat -e
• git log -5 --pretty="%H" | cat -e

Each of those three alternative commands inserted in 'git_commit.sh' provide the expected output:

yossi@hostname$ bash git_commit.sh | cat -e
42dfd4bdba4646b28136c4b0d71f76ae352aac10$
63a7f8e9e7f5ab2f29c4227440d78fc731201b89$
57361b98c8cb9041759461093ed38b7b8930e12e$
a05251da02f6c677f38f3ab68c95b2dd8812a822$
d17402aa3e3835e1b9e444482cda233e97e032d6$
yossi@hostname$

Is someone able to explain the difference in behavior of git log -5 --pretty="format:%H"?

Answer 1

The explanation lies here:

• tformat:
The tformat: format works exactly like format:, except that it provides "terminator" semantics instead of "separator" semantics. In other words, each commit has the message terminator character (usually a newline) appended, rather than a separator placed between entries. This means that the final entry of a single-line format will be properly terminated with a new line, just as the "oneline" format does. For example:

https://git-scm.com/docs/pretty-formats

Note that both git log --format="%H" and git log --pretty="%H" are equivalent to --pretty="tformat:%H":

--pretty[=<format>]
--format=<format>
Pretty-print the contents of the commit logs in a given format, where <format> can be one of oneline, short, medium, full, fuller, reference, email, raw, format:<string> and tformat:<string>. When <format> is none of the above, and has %placeholder in it, it acts as if --pretty=tformat:<format> were given.

https://git-scm.com/docs/git-log#Documentation/git-log.txt---prettyltformatgt