[tip][linux][shell] linux tips collections

[konosubakonoakua]

Dynamic variable names in Bash

#!/bin/sh
# In the container at runtime:
# export PROD_TOKEN="123"
env="PROD"
secret="${env}_TOKEN"
echo ${!secret}

[konosubakonoakua]

Shell-Parameter-Expansion

https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

[konosubakonoakua]

install location

• cmake

      cmake -DCMAKE_INSTALL_PREFIX=$HOME/.local

• configure

      ./configure --prefix=$HOME/.local

[konosubakonoakua]

LD_LIBRARY_PATH

Libraries have been installed in:
   /home/USER/.local/lib

If you ever happen to want to link against installed libraries
in a given directory, LIBDIR, you must either use libtool, and
specify the full pathname of the library, or use the `-LLIBDIR'
flag during linking and do at least one of the following:
   - add LIBDIR to the `LD_LIBRARY_PATH' environment variable
     during execution
   - add LIBDIR to the `LD_RUN_PATH' environment variable
     during linking
   - use the `-Wl,-rpath -Wl,LIBDIR' linker flag
   - have your system administrator add LIBDIR to `/etc/ld.so.conf'

See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so(8) manual pages.

❯ cat /etc/ld.so.conf.d/x86_64-linux-gnu.conf 
# Multiarch support
/usr/local/lib/x86_64-linux-gnu
/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu

echo
echo '== env =========================================================='
if [ -z ${LD_LIBRARY_PATH+x} ]; then
    echo "LD_LIBRARY_PATH is unset";
else
    echo LD_LIBRARY_PATH ${LD_LIBRARY_PATH} ;
fi

if [ -z ${LD_RUN_PATH+x} ]; then
    echo "LD_RUN_PATH is unset";
else
    echo LD_RUN_PATH ${LD_RUN_PATH} ;
fi

if [ -z ${DYLD_LIBRARY_PATH+x} ]; then
    echo "DYLD_LIBRARY_PATH is unset";
else
    echo DYLD_LIBRARY_PATH ${DYLD_LIBRARY_PATH} ;
fi
echo '================================================================='
echo
echo

[konosubakonoakua]

float point number comparison

use bc like echo "$1 < $2" | bc

ripgrep output only capture group

# only output capture group 1
rg '(group 1)...(group 2)' -or '$1'

libc version check

libc_ver_lt () {
  bc_cmd="$(ldd --version | rg 'GLIBC (\d\.\d{2})' -or '$1') < $1"
  return $(echo "$bc_cmd" | bc)
}