On Linux or Unix, error from a command (stderr) can be redirected to stdout or a file. These are the file descriptor id used on Linux for stdin, stdout and stderr.
| ID | Purpose |
|---|---|
| 0 | stdin (Standard input) |
| 1 | stdout (Standard output) |
| 2 | stderr (Standard error) |
stderr appended to stdout example
This can be useful when executing bash command from other programs like php shell_exec.
ls /etc/passwd_non_existing 2>&1
ls: cannot access /etc/passwd_non_existing: No such file or directory
Env: GNU bash, version 4.2.46
stderr appened to stdout and both redirected to a file
ls /etc/passwd_non_existing > tmp_file_all 2>&1 echo "==tmp_file_all==" cat tmp_file_all
==tmp_file_all== ls: cannot access /etc/passwd_non_existing: No such file or directory
Env: GNU bash, version 4.2.46
Only stderr redirected to file example
ls /etc/passwd_non_existing 2> tmp_file_err echo "==tmp_file_err==" cat tmp_file_err
==tmp_file_err== ls: cannot access /etc/passwd_non_existing: No such file or directory
Env: GNU bash, version 4.2.46
