With csh, tcsh, zsh or recent versions of bash, try

gcc hello.c |& tee file.txt

where

• |& instruct the shell to redirect standard error to standard output.

In other Bourne-like shells:

gcc hello.c 2>&1 | tee file.txt

With csh, tcsh, zsh or recent versions of bash, try

gcc hello.c |& tee file.txt

where

• |& instruct the shell to redirect standard error to standard output.

In other Bourne-like shells:

gcc hello.c 2>&1 | tee file.txt

In rc-like shells:

gcc hello.c >[2=1] | tee file.txt

In the fish shell:

gcc hello.c ^&1 | tee file.txt

try

gcc hello.c |& tee file.txt

where

• |& instruct the shell to redirect standard error to standard output.

With csh, tcsh, zsh or recent versions of bash, try

gcc hello.c |& tee file.txt

where

• |& instruct the shell to redirect standard error to standard output.

In other Bourne-like shells:

gcc hello.c 2>&1 | tee file.txt