The Open Group Base Specifications Issue 8 IEEE Std 1003.1-2024 sh — shell, the
standard command language interpreter says:
> When the shell is using standard input and it invokes a command that also uses
> standard input, the shell shall ensure that the standard input file pointer
> points directly after the command it has read when the command begins
> execution. It shall not read ahead in such a manner that any characters
> intended to be read by the invoked command are consumed by the shell (whether
> interpreted by the shell or not) or that characters that are not read by the
> invoked command are not seen by the shell.
We used the default BUFFER_SIZE for get_next_line of 1024, which caused us to
read ahead farther than was allowed by the Open Group Base Specification.
Setting BUFFER_SIZE=1 ensures that we don't read too far ahead, since
get_next_line will always immediatly stop once a newline is found.
This is for me the simplest way to solve this issue.
```
minishell$ ""
```
leads to the following error:
```
=================================================================
==1158770==ERROR: AddressSanitizer: attempting double-free on 0x5060000020c0 in thread T0:
#0 0x5649fcb5b8a8 in free.part.0 asan_malloc_linux.cpp.o
#1 0x5649fcbac549 in deal_with_filled_path /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:119:3
#2 0x5649fcbac38b in filepath_from_env /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:165:10
#3 0x5649fcbac220 in get_cmdpath /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:186:10
#4 0x5649fcba8664 in simple_cmd_execute /home/khais/src/42/common_env/minishell/src/executing/simple_cmd/simple_cmd_execute.c:71:8
#5 0x5649fcba6e4c in execute_command /home/khais/src/42/common_env/minishell/src/minishell.c:49:2
#6 0x5649fcba6ce5 in main /home/khais/src/42/common_env/minishell/src/minishell.c:92:3
#7 0x7fb4f2dcd27d in __libc_start_call_main (/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6+0x2a27d) (BuildId: 704cab5816f130c494208e8cc24d87a386ef085b)
#8 0x7fb4f2dcd338 in __libc_start_main@GLIBC_2.2.5 (/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6+0x2a338) (BuildId: 704cab5816f130c494208e8cc24d87a386ef085b)
#9 0x5649fca6f394 in _start (/home/khais/src/42/common_env/minishell/minishell+0x2b394)
0x5060000020c0 is located 0 bytes inside of 58-byte region [0x5060000020c0,0x5060000020fa)
freed by thread T0 here:
#0 0x5649fcb5b8a8 in free.part.0 asan_malloc_linux.cpp.o
#1 0x5649fcbac669 in select_path /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:81:3
#2 0x5649fcbac524 in deal_with_filled_path /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:116:9
#3 0x5649fcbac38b in filepath_from_env /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:165:10
#4 0x5649fcbac220 in get_cmdpath /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:186:10
#5 0x5649fcba8664 in simple_cmd_execute /home/khais/src/42/common_env/minishell/src/executing/simple_cmd/simple_cmd_execute.c:71:8
#6 0x5649fcba6e4c in execute_command /home/khais/src/42/common_env/minishell/src/minishell.c:49:2
#7 0x5649fcba6ce5 in main /home/khais/src/42/common_env/minishell/src/minishell.c:92:3
#8 0x7fb4f2dcd27d in __libc_start_call_main (/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6+0x2a27d) (BuildId: 704cab5816f130c494208e8cc24d87a386ef085b)
previously allocated by thread T0 here:
#0 0x5649fcb5c897 in malloc (/home/khais/src/42/common_env/minishell/minishell+0x118897)
#1 0x5649fcbac6be in alloc_path /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp_utils.c:34:9
#2 0x5649fcbac4e9 in deal_with_filled_path /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:113:15
#3 0x5649fcbac38b in filepath_from_env /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:165:10
#4 0x5649fcbac220 in get_cmdpath /home/khais/src/42/common_env/minishell/src/subst/simple_filename_exp.c:186:10
#5 0x5649fcba8664 in simple_cmd_execute /home/khais/src/42/common_env/minishell/src/executing/simple_cmd/simple_cmd_execute.c:71:8
#6 0x5649fcba6e4c in execute_command /home/khais/src/42/common_env/minishell/src/minishell.c:49:2
#7 0x5649fcba6ce5 in main /home/khais/src/42/common_env/minishell/src/minishell.c:92:3
#8 0x7fb4f2dcd27d in __libc_start_call_main (/nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6+0x2a27d) (BuildId: 704cab5816f130c494208e8cc24d87a386ef085b)
SUMMARY: AddressSanitizer: double-free asan_malloc_linux.cpp.o in free.part.0
==1158770==ABORTING
```
Looks like select_path frees filepath sometimes, no idea why. Removing these
lines didn't break any tests.
I'm pushing this to get a second opinion
