shell: errno memo

2021-04-07

Your open call just set errno to 26, you're in GDB and don't want to write another /tmp/test.new2.c to discover what just happened. Another day ruined.

The year is $current_year and I don't care to learn errno values.
Enough grepping around. Let's build a better tomorrow.

# $1: (nil) or errno value
# output: full errno list or errno value name
errno () {(
    err=${1}

    [ "$err" ] && filter="| grep \"${err}\""
    filter="$filter |column -t"
    cmdline="cc -E -dM /usr/include/errno.h \
            |grep 'define E' \
            |sort -n -k 3 \
            |cut -d' ' -f2- \
            $filter"
    eval $cmdline
)}

$ errno 26
ETXTBSY  26
ENOKEY   126
$ errno ENOBUFS
ENOBUFS  105

Your C compiler of choice will preprocess only an include from the command line, that happens to be the definition for errno codes on the system. After some text manipulation and formatting, a filter is applied, optionally a match on a name or a value.

So many seconds saved, now let's do something less productive.