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You can easily check the existing users and groups under a Linux or Unix-like systems such as HP-UX, AIX, FreeBSD, Apple OSX and more using the following commands:[donotprint][/donotprint]
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? How do I check if a file is empty in Bash?
You can use the find command and other options as follows. The -s option to the test builtin check to see if FILE exists and has a size greater than zero. It returns true and false values to indicate that file is empty or has some data. This page shows how to check if a file is empty in Bash shell running on a Linux or Unix-like operating systems.
The zero output indicate that file is not empty. So you can write a shell script as follows.
Mar 11, 2017 True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not. File1 - ot file2 True if file1 is older than file2, or if file2 exists and file1 does not.
- Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un.x-like operating systems. Is mkdir -p totally safe when creating folder already exists. Ask Question Asked 4 years. This implies to me that when the directory exists there is.
- Jun 09, 2018 You can easily find out if a regular file does or does not exist in Bash shell under macOS, Linux, FreeBSD, and Unix-like operating system. You can use expression expression , test expression, or if expression ; then. Fi in bash shell along with a!operator. Let us see various ways to find out if a file exists or not in bash shell.
You can easily check the existing users and groups under a Linux or Unix-like systems such as HP-UX, AIX, FreeBSD, Apple OSX and more using the following commands:[donotprint][/donotprint]
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[a] getent command : Fetch details for a particular user or group from a number of important text files called databases on a Linux or Unix-like systems. This is portable and recommended way to get information on users and groups.
Linux Sdm.dmg Does Not Exist Now
[b] Directly query /etc/passwd for user names or /etc/group file for group names.
Method #1: getent command to lookup username and group name
The syntax is as follows to find out if user named foo exists in system:
The syntax is as follows to find out if group named bar exists in system:
Sample demo of all commands:
Method #2: Find out if user exists in /etc/passwd file
/etc/passwd file stores essential information required during login. All you have to do is search this file for user name using the following syntax:
OR
For, example find out if vivek user exists or not, enter:
OR
Sample outputs:
grep username /etc/passwd
OR
egrep -i '^username' /etc/passwd
For, example find out if vivek user exists or not, enter:
$ egrep -i '^vivek' /etc/passwd
OR
$ egrep -i '^vivek:' /etc/passwd
Sample outputs:
A quick shell script code:
Normally, exit status is 0 returned if user accounts (lines) are found and 1 otherwise.
Use awk command to search user name
The syntax is as follows to search user named ‘apache’
Find out if group exists in /etc/group file
/etc/group is an text file which defines the groups to which users belong under Linux and UNIX operating system. Again, you have to search /etc/group file using following syntax:
For, example find out if vivek group exists or not, enter:
$ egrep -i '^groupname' /etc/group
For, example find out if vivek group exists or not, enter:
$ egrep -i '^vivek' /etc/group
Say hello to id command
The id command is another option to display user / group information for any USERNAME, or the current user. To find out more about user called, tom, enter:
Sample outputs:
$ id tom
Sample outputs:
id command exit status is 0 returned if user accounts (lines) are found and 1 otherwise. A sample shell script using id command:
Further readings:
- Man pages – group(5)
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You can use the find command and other options as follows. The -s option to the test builtin check to see if FILE exists and has a size greater than zero. It returns true and false values to indicate that file is empty or has some data. This page shows how to check if a file is empty in Bash shell running on a Linux or Unix-like operating systems.
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Check If File Is Empty Or Not Using Shell Script
The syntax is as follows:
Sample outputs:
Now create another file with some data in it:
You should not see any output from the find command.
Bash Script – Check If File is Empty or Not With the -s Option
However, one can pass the -s option as follows in script or shell prompt:
Sample outputs:
The non zero output indicate that file is empty.
Sample outputs:
The zero output indicate that file is not empty. So you can write a shell script as follows.
Shell Script To Check If File Is Empty OR Not
Run it as follows:
Sample outputs:
chmod +x script.sh
./script.sh /etc/resolv.conf
Sample outputs:
Run it on an empty file:
Sample outputs:
touch /tmp/test.txt
./script.sh /tmp/test.txt
Sample outputs:
Conclusion
This page showed how to check if file is empty on a Linux or Unix-like operating systems using various commands. See test command for more info.
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