How to redirect and append both stdout and stderr to a file with Bash

Question

To redirect stdout to a truncated file in Bash  I know to use   cmd  gt  file txt   To redirect stdout in Bash  appending to a file  I know to use   cmd  gt  gt  file txt   To redirect both stdout and stderr to a truncated file  I know to use   cmd  amp  gt  file txt   How do I redirect both stdout and stderr appending to a file  cmd  amp  gt  gt  file txt did not work for me

User · Answer

In Bash 4  as well as ZSH 4 3 11    cmd  amp  gt  gt outfile   just out of box

User · Answer

This should work fine   your command 2 gt  amp 1   tee -a file txt   It will store all logs in file txt as well as dump them on terminal

User · Answer

In Bash you can also explicitly specify your redirects to different files   cmd  gt log out 2 gt log error out   Appending would be   cmd  gt  gt log out 2 gt  gt log error out

User · Answer

I am surprised that in almost ten years  no one has posted this approach yet  If using older versions of bash where  amp  gt  gt  isn t available  you also can do   cmd 2 gt  amp 1   gt  gt  file txt  This spawns a subshell  so it s less efficient than the traditional approach of cmd  gt  gt  file txt 2 gt  amp 1  and it consequently won t work for commands that need to modify the current shell  e g  cd  pushd   but this approach feels more natural and understandable to me   Redirect stderr to stdout  Redirect the new stdout by appending to a file   Also  the parentheses remove any ambiguity of order  especially if you want to pipe stdout and stderr to another command instead  Edit  To avoid starting a subshell  you instead could use curly braces instead of parentheses to create a group command    cmd 2 gt  amp 1     gt  gt  file txt   Note that a semicolon  or newline  is required to terminate the group command

User · Answer

There are two ways to do this  depending on your Bash version   The classic and portable  Bash pre-4  way is   cmd  gt  gt  outfile 2 gt  amp 1   A nonportable way  starting with Bash 4 is  cmd  amp  gt  gt  outfile    analog to  amp  gt  outfile   For good coding style  you should   decide if portability is a concern  then use classic way  decide if portability even to Bash pre-4 is a concern  then use classic way  no matter which syntax you use  not change it within the same script  confusion     If your script already starts with    bin sh  no matter if intended or not   then the Bash 4 solution  and in general any Bash-specific code  is not the way to go   Also remember that Bash 4  amp  gt  gt  is just shorter syntax     it does not introduce any new functionality or anything like that   The syntax is  beside other redirection syntax  described here  http   bash-hackers org wiki doku php syntax redirection appending redirected output and error output

User · Answer

cmd  gt  gt file txt 2 gt  amp 1   Bash executes the redirects from left to right as follows     gt  gt file txt  Open file txt in append mode and redirect stdout there  2 gt  amp 1  Redirect stderr to  where stdout is currently going   In this case  that is a file opened in append mode  In other words  the  amp 1 reuses the file descriptor which stdout currently uses

User · Answer

Try this  You command 1 gt output log  2 gt  amp 1   Your usage of  amp  x file does work in bash4  sorry for that      Here comes some additional tips   0  1  2   9 are file descriptors in bash    0 stands for stdin  1 stands for stdout  2 stands for stderror  3 9 is spare for any other temporary usage   Any file descriptor can be redirected to other file descriptor or file by using operator  gt  or  gt  gt  append    Usage    lt file descriptor gt     lt filename    amp file descriptor gt   Please reference to http   www tldp org LDP abs html io-redirection html

[bash] How to redirect and append both stdout and stderr to a file with Bash?

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