dema@o2-nixos  ~/nixos/nixpkgs   dema ●✚  strace -ff -e execve nix-shell -p                                                                                             ~/nixos/nixpkgs
execve("/run/current-system/sw/bin/nix-shell", ["nix-shell", "-p"], 0x7ffe496ea0a0 /* 94 vars */) = 0
strace: Process 2392 attached
strace: Process 2393 attached
strace: Process 2394 attached
strace: Process 2395 attached
[pid  2391] execve("/nix/store/m7v6p7yxqyhnc4sxp49zp857cjamp996-bash-interactive-4.4-p23/bin/bash", ["bash", "--rcfile", "/tmp/nix-shell-2391-0/rc"], 0x2f00790 /* 127 vars */ <unfinished ...>
[pid  2394] +++ exited with 0 +++
[pid  2392] +++ exited with 0 +++
[pid  2393] +++ exited with 0 +++
[pid  2395] +++ exited with 0 +++
<... execve resumed>)                   = 0
strace: Process 2404 attached
[pid  2404] +++ exited with 1 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2404, si_uid=1000, si_status=1, si_utime=0, si_stime=0} ---
strace: Process 2405 attached
strace: Process 2406 attached
[pid  2406] execve("/nix/store/gnw6yrqy249n62r4q8vy12ispviv3dav-coreutils-8.31/bin/nproc", ["nproc"], 0x1666008 /* 154 vars */) = 0
[pid  2406] +++ exited with 0 +++
[pid  2405] --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2406, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
[pid  2405] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2405, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
strace: Process 2407 attached
[pid  2407] execve("/nix/store/gnw6yrqy249n62r4q8vy12ispviv3dav-coreutils-8.31/bin/expr", ["expr", "4", ":", "^[0-9][0-9]*$"], 0x1666008 /* 154 vars */) = 0
[pid  2407] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2407, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
strace: Process 2408 attached
[pid  2408] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2408, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---

[nix-shell:~/nixos/nixpkgs]$