update-alternatives

gcc-update-alternatives.sh

#!/usr/bin/env bash

test -n "$DEBUG" && set -x

#                      __ __       ___
#                     /\ \\ \    /'___`\
#                     \ \ \\ \  /\_\ /\ \
#                      \ \ \\ \_\/_/// /__
#                       \ \__ ,__\ // /_\ \
#                        \/_/\_\_//\______/
#                           \/_/  \/_____/
#                                         Algoritimos
#
#
#      Author: Ivan Lopes
#        Mail: ivan@42algoritmos.com.br
#        Site: http://www.42algoritmos.com.br
#     License: gpl
#       Phone: +1 561 801 7985
#    Language: Shell Script
#        File: u.sh
#        Date: Sex 03 Ago 2018 03:39:01 -03
# Description:
# ----------------------------------------------------------------------------
# Modo strict
set -euo pipefail
# ----------------------------------------------------------------------------

##############################################################################
##############################################################################
##############################################################################

# ----------------------------------------------------------------------------
versions=(
5 6 7 8
)

let i=50

for v in ${versions[*]}; do
    echo -e '\e[1;49;36m'gcc-${v}'\e[0m' >&2
    echo -n sudo update-alternatives
    echo -n " "--install /usr/bin/gcc gcc /usr/bin/gcc-$v $i
    dpkg -L gcc-$v g++-$v|
        awk -F'/bin/' '/.*bin\// {print $2}' |
            while read line; do
                [[ "$line" == "gcc-$v" ]] && continue
                cmd=${line%-*}
                echo -n " "--slave /usr/bin/$cmd $cmd /usr/bin/$line
            done
    echo
    let i=$((i + 10))

done

# ----------------------------------------------------------------------------
exit 0

Thanks for this, very useful! Helped me fix an issue where I thought I was building python with gcc 10, but because the generated python make file used x86_64-linux-gnu-gcc and not gcc, it was actually building with gcc 9...

On Ubuntu 20.04, with gcc9 and gcc10, I refactored this and generated the command to use via:

versions=(9 10)
i=90
for v in ${versions[*]}; do
    echo -e '\e[1;49;36m'"gcc-${v}"'\e[0m' >&2
    cmd_str_install="sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$v $i\n"
    cmd_str_slaves=$(
        dpkg -L "gcc-$v" "g++-$v" |
            awk -F'/bin/' '/.*bin\// {print $2}' |
                while read -r line; do
                    [[ "$line" == "gcc-$v" ]] && continue
                    cmd=${line%-*}
                    echo "  --slave /usr/bin/$cmd $cmd /usr/bin/$line"
                done
    )
    # remove trailing newline and backslash split each slave section
    echo -ne "$cmd_str_install$cmd_str_slaves" | sed -z 's/\n$//' | sed -z 's/\n/ \\\n/g'
    echo
    i=$((i + 10))
done

It generated:

gcc-9
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 90 \
  --slave /usr/bin/x86_64-linux-gnu-gcc x86_64-linux-gnu-gcc /usr/bin/x86_64-linux-gnu-gcc-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ar x86_64-linux-gnu-gcc-ar /usr/bin/x86_64-linux-gnu-gcc-ar-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-nm x86_64-linux-gnu-gcc-nm /usr/bin/x86_64-linux-gnu-gcc-nm-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ranlib x86_64-linux-gnu-gcc-ranlib /usr/bin/x86_64-linux-gnu-gcc-ranlib-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcov x86_64-linux-gnu-gcov /usr/bin/x86_64-linux-gnu-gcov-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcov-dump x86_64-linux-gnu-gcov-dump /usr/bin/x86_64-linux-gnu-gcov-dump-9 \
  --slave /usr/bin/x86_64-linux-gnu-gcov-tool x86_64-linux-gnu-gcov-tool /usr/bin/x86_64-linux-gnu-gcov-tool-9 \
  --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-9 \
  --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-9 \
  --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-9 \
  --slave /usr/bin/gcov gcov /usr/bin/gcov-9 \
  --slave /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-9 \
  --slave /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-9 \
  --slave /usr/bin/x86_64-linux-gnu-g++ x86_64-linux-gnu-g++ /usr/bin/x86_64-linux-gnu-g++-9 \
  --slave /usr/bin/g++ g++ /usr/bin/g++-9
gcc-10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100 \
  --slave /usr/bin/x86_64-linux-gnu-gcc x86_64-linux-gnu-gcc /usr/bin/x86_64-linux-gnu-gcc-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ar x86_64-linux-gnu-gcc-ar /usr/bin/x86_64-linux-gnu-gcc-ar-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-nm x86_64-linux-gnu-gcc-nm /usr/bin/x86_64-linux-gnu-gcc-nm-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ranlib x86_64-linux-gnu-gcc-ranlib /usr/bin/x86_64-linux-gnu-gcc-ranlib-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcov x86_64-linux-gnu-gcov /usr/bin/x86_64-linux-gnu-gcov-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcov-dump x86_64-linux-gnu-gcov-dump /usr/bin/x86_64-linux-gnu-gcov-dump-10 \
  --slave /usr/bin/x86_64-linux-gnu-gcov-tool x86_64-linux-gnu-gcov-tool /usr/bin/x86_64-linux-gnu-gcov-tool-10 \
  --slave /usr/bin/x86_64-linux-gnu-lto-dump x86_64-linux-gnu-lto-dump /usr/bin/x86_64-linux-gnu-lto-dump-10 \
  --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-10 \
  --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-10 \
  --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-10 \
  --slave /usr/bin/gcov gcov /usr/bin/gcov-10 \
  --slave /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-10 \
  --slave /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-10 \
  --slave /usr/bin/lto-dump lto-dump /usr/bin/lto-dump-10 \
  --slave /usr/bin/x86_64-linux-gnu-g++ x86_64-linux-gnu-g++ /usr/bin/x86_64-linux-gnu-g++-10 \
  --slave /usr/bin/g++ g++ /usr/bin/g++-10

Updated for 24.04 with gcc versions 13 & 14 and handled separate packages for /usr/bin/x86_64-linux-gnu-gcc & /usr/bin/x86_64-linux-gnu-g++:

versions=(13 14)
i=10
for v in ${versions[*]}; do
    echo -e '\e[1;49;36m'"gcc-${v}"'\e[0m' >&2
    cmd_str_install="sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$v $i\n"
    cmd_str_slaves=$(
        dpkg -L "gcc-$v" "g++-$v" "gcc-$v-x86-64-linux-gnu" "g++-$v-x86-64-linux-gnu" |
            awk -F'/bin/' '/.*bin\// {print $2}' |
                while read -r line; do
                    [[ "$line" == "gcc-$v" ]] && continue
                    cmd=${line%-*}
                    echo "  --slave /usr/bin/$cmd $cmd /usr/bin/$line"
                done
    )
    # remove trailing newline and backslash split each slave section
    echo -ne "$cmd_str_install$cmd_str_slaves" | sed -z 's/\n$//' | sed -z 's/\n/ \\\n/g'
    echo
    i=$((i + 10))
done