Command Line Standard Error
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Getting Started Examples Links Tools Books ADSI Getting Started Examples Links Tools Books Silent Installs General Windows Installer Specific Software Software Requirements Hardware Requirements Books Batch Files Windows Resource Kits KiXtart Perl PowerShell https://support.microsoft.com/en-us/kb/110930 Regular Expressions Rexx VBScript & WSH C# WMI ADSI HTML, JavaScript & CSS Off-Topic Scripting Tools Batch Utilities Resource Kits Compilers Editors Code Generators Regular Expressions Automation Tools VBScript Add-Ons Visual Studio Printing Tools Inventory Tools Shell Extensions File Viewers Backup Security The making Of... Miscellaneous Tweaks Web Stuff Conversions My Photo Galleries About This Site Disclaimer News FAQ Search What's New Objective Site Policy http://www.robvanderwoude.com/redirection.php Your Preferences Credits The Making Of... Contact Failed Mail Donate Redirection Redirection command > file Write standard output of command to file command 1> file Write standard output of command to file (same as previous) command 2> file Write standard error of command to file (OS/2 and NT) command > file 2>&1 Write both standard output and standard error of command to file (OS/2 and NT) command >> file Append standard output of command to file command 1>> file Append standard output of command to file (same as previous) command 2>> file Append standard error of command to file (OS/2 and NT) command >> file 2>&1 Append both standard output and standard error of command to file (OS/2 and NT) commandA | commandB Redirect standard output of commandA to standard input of commandB commandA 2>&1 | commandB Redirect standard output and standard error of commandA to standard input of commandB (OS/2 and NT) command < file command gets standard input from file command 2>&1 command's standard error is redirected to standard output (OS/2 and NT) command 1>&2 command's standard output is redirected to standard error (OS/2 and NT) Notes: (1) Where the ta
a filename to make a program take input from a file. stdout (standard output) by default is printed on your computer screen. We can use ">" with a filename to send that to a file, overwriting whatever is there, or we can use ">>" http://en.flossmanuals.net/command-line/standard-files/ to append standard output to the end of the file. stderr (standard error) is an alternative http://ss64.com/nt/syntax-redirection.html kind of output. Programs use it to send error messages. This can be useful because you might want to see error messages on the terminal even if you redirect output to a file. Here's an example: $ ls *.bak > listfile ls: *.bak: No such file or directory Here, we wanted a list of all files ending in .bak. But no such files exist in this command line directory. If ls sent its error message to standard output (which in this case has been directed to a file), we wouldn't know that there is a problem without looking at the content of listfile. But because ls sent its message to standard error, we see it. The error message starts with the name of the program (ls) followed by a colon and the actual message. A pipe simply redirects the standard output of the first program to the standard input of windows redirect stderr the second: $ ls *.bak | more Sometimes, we want to direct the output of a command to a file, but we also want to see the output as the program runs. The tee command does just that: $ ls -lR / | tee allMyFiles provides a complete, detailed list of your file system, saved to allMyFiles. This takes some time to run; tee saves you from staring at a lifeless screen, wondering whether any thing's happening. Each program can open a lot of files, and each has a number called a file descriptor that is meaningful only within that program. The first three numbers are always reserved for the file descriptors we just described. stdin 0 stdout 1 stderr 2 Redirecting stderrWhen we redirect stdin as we did above, error messages still go to the screen. For example $ ls /nosuchplace > /dev/null ls: /nosuchplace: No such file or directory $ To redirect stderr we have to use the more general form of redirection, which uses the file numbers mentioned in the previous section, and looks like this. $ ls /nosuchplace 2>/tmp/errors $ This sends the error message sent to file number 2 (stderr) into the file /tmp/errors. Now we can introduce a more complex redirection, which redirects standard output and standard error to the same file: $ ls *.bak > listfile 2>&1 The & in that command has nothing to do with putting a command in the background. The & here must di
commandB commandA & commandB Run commandA and then run commandB commandA && commandB Run commandA, if it succeeds then run commandB commandA || commandB Run commandA, if it fails then run commandB commandA && commandB || commandC If commandA succeeds run commandB, if it fails commandC Success and failure are based on the Exit Code of the command. In most cases the Exit Code is the same as the ErrorLevel Numeric handles: STDIN = 0 Keyboard input STDOUT = 1 Text output STDERR = 2 Error text output UNDEFINED = 3-9 command 2> filename Redirect any error message into a file command 2>> filename Append any error message into a file (command)2> filename Redirect any CMD.exe error into a file command > file 2>&1 Redirect errors and output to one file command > fileA 2> fileB Redirect output and errors to separate files command 2>&1 >filename This will fail! Redirect to NUL (hide errors) command 2> nul Redirect error messages to NUL command >nul 2>&1 Redirect error and output to NUL command >filename 2> nul Redirect output to file but suppress error (command)>filename 2> nul Redirect output to file but suppress CMD.exe errors Any long filenames must be surrounded in "double quotes". A CMD error is an error raised by the command processor itself rather than the program/command. Redirection with > or 2> will overwrite any existing file. You can also redirect to a printer with > PRN or >LPT1 Multiple commands on one line In a batch file the default behaviour is to read and expand variables one line at a time, if you use & to run multiple commands on a single line, then any variable changes will not be visible until execution moves to the next line. For example: SET /P _cost="Enter the price: " & ECHO %_cost% This behaviour can be changed using SETLOCAL EnableDelayedExpansion Creating a new file Create empty files using the NUL device: Type NUL >EmptyFile.txt or Copy NUL EmptyFile.txt To pre