Create a new bash file, named, and enter the script below. In this case you can omit the 2 from the redirection, but you will lose any output from the command. It is a part of the package moreutils in most distros. Check to see if a variable is empty or not. 2.1: Method-1: Using single or double brackets ... We can use find command and then suppress the output to check if the target directory has some content or not. Also, since any bash test without an argument will always return true, it is advisable to quote the variables so that the test will have at least an (empty) argument, irrespective of whether the variable is set or not. If command writes errors out to stderr, you can use the form command 2> /dev/null && echo OK || echo Failed.The 2> /dev/null redirects stderr output to /dev/null.However, some utilities will write errors to stdout (even though this is bad practice). H ow do I check if a file is empty or not using bash or ksh shell script under a UNIX / Linux / macOS / OS X / BSD family of operating systems? To test for whitespace characters, the $'…' syntax is specific to ksh/bash/zsh; you can insert these characters in your script literally (note that a newline will have to be within quotes, as backslash+newline expands to nothing), or generate them, e.g. You can quickly test for null or empty variables in a Bash shell script. If the command (at -l) command returns no value (is empty/null) then write a message to the file in place of the command output. Note that if the standard input is not empty, it is passed through ifne in this case. -name core | ifne mail … check_empty.sh and execute with our without command line arguments: $ bash check_empty.sh Empty Variable 1 Empty Variable 3 Empty Variable 5 Furthermore, the execution of the above script with a command line argument will trigger opposite results: $ bash check_empty.sh hello Not Empty Variable 2 Not Empty Variable 4 Not empty Variable 5 Several other tests allow you to check things such as the permissions of the file. #!/bin/bash if [ $(whoami) = 'root' ]; then echo "You are root" fi. Checking $? The whoami command outputs the username. The test command is frequently used as part of a conditional expression . Run the command if the standard input is emp- ty. You can use the help command for other builtins too.. OPTIONS -n Reverse operation. returns success (0) as the command ran but the return from the command is empty. From the bash variables tutorial, you know that $(command) syntax is used for command substitution and it gives you the output of the command. How do I check if a file is empty in Bash? You need to pass the -z or -n option to the test command or to the if command or use conditional expression.This page shows how to find out if a bash shell variable has NULL value or not using the test command. You can use the find command and other options as follows. Appreciate any help, thanks. DESCRIPTION ifne runs the following command if and only if the standard input is not empty. In some distributions, it is not installed by default. The condition $(whoami) = 'root' will be true only if you are logged in as the root user. A simple solution is to use ifne command (if input not empty). For instance, the following statement says, "If 4 is greater than 5, output yes, otherwise output no." Bash/Shell: Check if file exists (is empty or not empty) To check if the file exists and if it is empty or if it has some content then we use "-s" attribute . Note that if the standard input is not empty, it is passed through ifne to the given command My problem is around trapping the empty returned command value and replacing with my own message. test provides no output, but returns an exit status of 0 for "true" (test successful) and 1 for "false" (test failed). @echo off setlocal rem Subversion sends through the path to the repository and transaction id set REPOS=%1 set TXN=%2 rem check for an empty log message svnlook log %REPOS% -t %TXN% | findstr . ifne runs a given command if and only if the standard input is not empty. > nul if %errorlevel% gtr 0 (goto err) else exit 0 :err echo. EXAMPLE find . See the man pages for bash for more details or use help test to see brief information on the test builtin. 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