Linux error messages on one line

How to redirect standard (stderr) error in bash

I am trying to redirect bash message into file named output.log. But, it is not getting redirected. How do I redirect both standard output and standard error in bash shell? In Linux, how do I redirect error messages?

Standard error (also known as stderr) is the default error output device. Use stderr to write all system error messages. The number (FD – File Descriptors) two (2) denotes the stderr. The default stderr is the screen or monitor. Standard output (also known as stdout) is used by a command to writes (display) its output. The default stdout is the screen. It is denoted by one number (1).

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	Linux, macOS or Unix-like OS with Bash
Est. reading time	3 minutes

2> is input redirection symbol and syntax is:

1. To redirect stderr (standard error) to a file:
   command 2> errors.txt
2. Let us redirect both stderr and stdout (standard output):
   command &> output.txt
3. Finally, we can redirect stdout to a file named myoutput.txt, and then redirect stderr to stdout using 2>&1 (errors.txt):
   command > out 2>errors.txt

Make sure you use >> for appending data/log if the file already has data. For instance:

How to redirect standard error in bash

Run find command and save all error messages to find.error.txt file:
find / -name «*.conf» 2> find.error.txt
You can view find.error.txt with the cat command:
cat find.error.txt
Sample outputs:

You need to use “2>” when you want to redirect stderr to a file. You can redirect stdout to file named results.txt and stderr to file named errors.txt:
find / -name «*.conf» >results.txt 2>error.txt
Verify results with the cat command:
cat results.txt
cat error.txt
This is useful in shell scripts or any other purpose.

How to redirect standard error and standard output in bash

You can send both stdout and stderr to a file named output.txt
command &>output.xt
find / -name «*.pl» &>filelist.txt
Please note that both errors and actual output of the find command stored into a file:
cat filelist.txt
Sample outputs:

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Summary

Command	Description/Purpose
command 2>filename	Redirect stderr to filename
command >output.txt 2>error.log cat output.txt error.txt	Redirect stderr to file named error.log and stdout to file named output.txt
command &> filename	Redirect stderr and stdout to filename
command 2>&-	Just suppress error messages. No file created. No error message displayed on screen
command 1>&2 Sample code:

Redirect error messages to standard output. Useful in shell script when you need to forcefully display error messages on screen

For more info see bash man page online or read it at the cli by using the man command:
man bash

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Comments on this entry are closed.

The numbers are actually file descriptors.

• 0 = stdin
• 1 = stdout
• 2 = stderr

yes they are. thanks for comment.

Hi, Vitek!
It seems there is a mistake in your article, specifically the fifth example in your conclusive summarizing table is wrong in my opinion. I had tried to post you a reply, but it turned to be too long and the site refused to accept it. So I designed it as a text file, zipped it as a tar archive and uploaded to a filehosting. Please take some time, download it and read my message. Perhaps I’m wrong, still it seems to me, I’ve found a flaw in your article.

I can’t find your zip file. However, I updated my 5th example.

I have read your article “How to Redirect Standard Error in Bash” on the link https://www.cyberciti.biz/faq/how-to-redirect-standard-error-in-bash/ dedicated to the redirection of standard input/output streams,
however I couldn’t understand the meaning of your last instruction in the article and the example below.

Redirect error messages to standard output. Useful in shell script when you need
to forcefully display error messages on screen

The 2>&1 command really redirects stderr to stdout, but it seems in most cases this construction won’t work as it was thought out. In your example you redirect the stderr of echo, but echo always sends its output to stdout, not stderr, thus this redirection will take no effect and the “File not found” message will be sent to stdout any case. On the other hand, if the standard output has been already redirected to some file, say “msg.txt”, the 2>&1 construction will redirect stderr to the same “msg.txt” file and put all your error messages together with normal output.

I think what you really meant was the construction 1>&2 which redirects stdout to stderr. Then the standard output of the script may be redirected to some file or a pipe, still the error messages will appear on the screen or a terminal. So your instruction possibly should be rewritten in some way like:

Redirect error messages from standard output to standard error stream. Useful in a shell script when you need to forcefully display error messages on the screen, no matter was the script’s output redirected to a file or a pipe or not. The construction is useful with commands like echo or printf, which always print the text to the standard output, and makes them print error messages to the standard error stream.

Per contra, the 2>&1 operator is useful when you want your script’s or program’s error messages to get to the same stream as normal output. In that case it must be preceded by the stdout redirection, otherwise it won’t work. For example,

As far as I know, it’s a common practice to use in modern shells a brief simplified notation:

instead of the old traditional

but the meaning of both notations (modern simplified and the old verbose one)
is quite the same. Please look through my post and comment it. I’m not a shell programming expert, so I may be wrong, but it seems I’ve found a small mistake in your article.

Thanks. I fixed the page. I appreciate your feedback.

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Appendix B Unix Error Messages

Errors generated by the failure of a system call or library function, can be displayed using the perror or strerror library function calls (see «Managing Failures» Section 1.5, «Managing System Call Failures»). For example, the error messages returned by strerror on a Linux system can be displayed in their entirety using Program B.1.

Program B.1 Displaying strerror messages.

| extern int sys_nerr;

+ using namespace std;

| cout « err« ‘\t’ « strerror(err) « endl;

As the output of the program will fill more than one screen, it may be helpful to redirect the output to either a file, for future reference, or to the more command to permit viewing of the output at a controlled pace. To compile the source file and capture the output of the program in a file called emessages, the command sequence is linux$ g++ errors.cxx -o errors linux$ errors > emessages

If, after compilation, you want the program output to be piped to more, the command sequence is linux$ errors | more

Note that the error message returned by strerror (and perror) in a C/C++ program is the same message that is returned by the Linux command-line utility called perror. A command-line sequence to determine the error message associated with error number 13 is linux$ perror 13

Error code 13: Permission denied

A Bourne shell script that uses the command-line perror utility to display all error messages is shown in Program B.2.

Program B.2 Bourne shell script that uses perror to generate error messages.

| while test $err-It 125; do | echo -n «$err » + perror -s $err | err=’expr $err + 1′ | done

Table B.1 lists the error number, its symbolic name, and the actual message generated by strerror.

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greggyNapalm / gist:2413028

# @see /usr/include/asm-generic/errno-base.h

#ifndef _ASM_GENERIC_ERRNO_BASE_H

#define _ASM_GENERIC_ERRNO_BASE_H

#define EPERM 1 /* Operation not permitted */

#define ENOENT 2 /* No such file or directory */

#define ESRCH 3 /* No such process */

#define EINTR 4 /* Interrupted system call */

#define EIO 5 /* I/O error */

#define ENXIO 6 /* No such device or address */

#define E2BIG 7 /* Argument list too long */

#define ENOEXEC 8 /* Exec format error */

#define EBADF 9 /* Bad file number */

#define ECHILD 10 /* No child processes */

#define EAGAIN 11 /* Try again */

#define ENOMEM 12 /* Out of memory */

#define EACCES 13 /* Permission denied */

#define EFAULT 14 /* Bad address */

#define ENOTBLK 15 /* Block device required */

#define EBUSY 16 /* Device or resource busy */

#define EEXIST 17 /* File exists */

#define EXDEV 18 /* Cross-device link */

#define ENODEV 19 /* No such device */

#define ENOTDIR 20 /* Not a directory */

#define EISDIR 21 /* Is a directory */

#define EINVAL 22 /* Invalid argument */

#define ENFILE 23 /* File table overflow */

#define EMFILE 24 /* Too many open files */

#define ENOTTY 25 /* Not a typewriter */

#define ETXTBSY 26 /* Text file busy */

#define EFBIG 27 /* File too large */

#define ENOSPC 28 /* No space left on device */

#define ESPIPE 29 /* Illegal seek */

#define EROFS 30 /* Read-only file system */

#define EMLINK 31 /* Too many links */

#define EPIPE 32 /* Broken pipe */

#define EDOM 33 /* Math argument out of domain of func */

#define ERANGE 34 /* Math result not representable */

#endif

# @see /usr/include/asm-generic/errno.h

#ifndef _ASM_GENERIC_ERRNO_H

#define _ASM_GENERIC_ERRNO_H

#include

#define EDEADLK 35 /* Resource deadlock would occur */

#define ENAMETOOLONG 36 /* File name too long */

#define ENOLCK 37 /* No record locks available */

#define ENOSYS 38 /* Function not implemented */

#define ENOTEMPTY 39 /* Directory not empty */

#define ELOOP 40 /* Too many symbolic links encountered */

#define EWOULDBLOCK EAGAIN /* Operation would block */

#define ENOMSG 42 /* No message of desired type */

#define EIDRM 43 /* Identifier removed */

#define ECHRNG 44 /* Channel number out of range */

#define EL2NSYNC 45 /* Level 2 not synchronized */

#define EL3HLT 46 /* Level 3 halted */

#define EL3RST 47 /* Level 3 reset */

#define ELNRNG 48 /* Link number out of range */

#define EUNATCH 49 /* Protocol driver not attached */

#define ENOCSI 50 /* No CSI structure available */

#define EL2HLT 51 /* Level 2 halted */

#define EBADE 52 /* Invalid exchange */

#define EBADR 53 /* Invalid request descriptor */

#define EXFULL 54 /* Exchange full */

#define ENOANO 55 /* No anode */

#define EBADRQC 56 /* Invalid request code */

#define EBADSLT 57 /* Invalid slot */

#define EDEADLOCK EDEADLK

#define EBFONT 59 /* Bad font file format */

#define ENOSTR 60 /* Device not a stream */

#define ENODATA 61 /* No data available */

#define ETIME 62 /* Timer expired */

#define ENOSR 63 /* Out of streams resources */

#define ENONET 64 /* Machine is not on the network */

#define ENOPKG 65 /* Package not installed */

#define EREMOTE 66 /* Object is remote */

#define ENOLINK 67 /* Link has been severed */

#define EADV 68 /* Advertise error */

#define ESRMNT 69 /* Srmount error */

#define ECOMM 70 /* Communication error on send */

#define EPROTO 71 /* Protocol error */

#define EMULTIHOP 72 /* Multihop attempted */

#define EDOTDOT 73 /* RFS specific error */

#define EBADMSG 74 /* Not a data message */

#define EOVERFLOW 75 /* Value too large for defined data type */

#define ENOTUNIQ 76 /* Name not unique on network */

#define EBADFD 77 /* File descriptor in bad state */

#define EREMCHG 78 /* Remote address changed */

#define ELIBACC 79 /* Can not access a needed shared library */

#define ELIBBAD 80 /* Accessing a corrupted shared library */

#define ELIBSCN 81 /* .lib section in a.out corrupted */

#define ELIBMAX 82 /* Attempting to link in too many shared libraries */

#define ELIBEXEC 83 /* Cannot exec a shared library directly */

#define EILSEQ 84 /* Illegal byte sequence */

#define ERESTART 85 /* Interrupted system call should be restarted */

#define ESTRPIPE 86 /* Streams pipe error */

#define EUSERS 87 /* Too many users */

#define ENOTSOCK 88 /* Socket operation on non-socket */

#define EDESTADDRREQ 89 /* Destination address required */

#define EMSGSIZE 90 /* Message too long */

#define EPROTOTYPE 91 /* Protocol wrong type for socket */

#define ENOPROTOOPT 92 /* Protocol not available */

#define EPROTONOSUPPORT 93 /* Protocol not supported */

#define ESOCKTNOSUPPORT 94 /* Socket type not supported */

#define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */

#define EPFNOSUPPORT 96 /* Protocol family not supported */

#define EAFNOSUPPORT 97 /* Address family not supported by protocol */

#define EADDRINUSE 98 /* Address already in use */

#define EADDRNOTAVAIL 99 /* Cannot assign requested address */

#define ENETDOWN 100 /* Network is down */

#define ENETUNREACH 101 /* Network is unreachable */

#define ENETRESET 102 /* Network dropped connection because of reset */

#define ECONNABORTED 103 /* Software caused connection abort */

#define ECONNRESET 104 /* Connection reset by peer */

#define ENOBUFS 105 /* No buffer space available */

#define EISCONN 106 /* Transport endpoint is already connected */

#define ENOTCONN 107 /* Transport endpoint is not connected */

#define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */

#define ETOOMANYREFS 109 /* Too many references: cannot splice */

#define ETIMEDOUT 110 /* Connection timed out */

#define ECONNREFUSED 111 /* Connection refused */

#define EHOSTDOWN 112 /* Host is down */

#define EHOSTUNREACH 113 /* No route to host */

#define EALREADY 114 /* Operation already in progress */

#define EINPROGRESS 115 /* Operation now in progress */

#define ESTALE 116 /* Stale NFS file handle */

#define EUCLEAN 117 /* Structure needs cleaning */

#define ENOTNAM 118 /* Not a XENIX named type file */

#define ENAVAIL 119 /* No XENIX semaphores available */

#define EISNAM 120 /* Is a named type file */

#define EREMOTEIO 121 /* Remote I/O error */

#define EDQUOT 122 /* Quota exceeded */

#define ENOMEDIUM 123 /* No medium found */

#define EMEDIUMTYPE 124 /* Wrong medium type */

#define ECANCELED 125 /* Operation Canceled */

#define ENOKEY 126 /* Required key not available */

#define EKEYEXPIRED 127 /* Key has expired */

#define EKEYREVOKED 128 /* Key has been revoked */

#define EKEYREJECTED 129 /* Key was rejected by service */

/* for robust mutexes */

#define EOWNERDEAD 130 /* Owner died */

#define ENOTRECOVERABLE 131 /* State not recoverable */

#define ERFKILL 132 /* Operation not possible due to RF-kill */

#endif

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